The process of making a printed circuit board at home. Printed circuit

Device diagram

It makes no significant difference whether we lay out the board on a piece of paper in a checkered pattern, cutting out templates of parts with pins from cardboard (although I deeply doubt that anyone will use this method in the 21st century, when every home has a computer), or use some program for PCB layout, for example sprint layout. Of course, with the help of sprint layout it will be much easier to do this, especially in large schemes. In both cases, first we place on the working field the part with the largest number of pins; in our case it is a transistor, let’s say VT1, this is our KT315. (A link to the sprint layout user manual will be provided below). Moreover, at first, when designing, your printed circuit board may resemble a circuit diagram, that’s okay, I think everyone started out that way. We installed it, then we connect its base and emitter with tracks to resistor R1, we also have the base VT1 connected to the output of capacitor C1 and the output of resistor R2. Instead of lines on the diagram, we connect the pins of the parts with a track on the printed circuit board. I also made it a rule to count the number of pins of parts connected on the diagram and on the printed circuit board; we should get the same number of connected patches.

As you can see, we have 3 more pins connected to the base on the board, just like in the diagram; in the diagram they are marked with red rings. Next, we install transistor VT2 - this is a KT361 transistor, it has a pnp structure, but we don’t care at the moment, since it also has 3 outputs and is in a housing exactly the same as KT315. We installed the transistor, then connect its emitter to the second terminal R2, and the second terminal of capacitor C1 to the collector VT2. We connect the VT2 base to the VT1 collector, install patches on the board to connect the BA1 speaker, we connect it with one terminal to the VT2 collector, the other terminal to the VT1 emitter. Here's what everything I described looks like on the board:

We continue further, we install the LED, connect it to the BA1 pin and to the VT2 emitter. Afterwards we install transistor VT3, this is also KT315 and connect it with the collector to the cathode of the LED, we connect the emitter of VT3 to the minus of the power supply. Next, we install resistor R4 and connect it with tracks to the base and emitter of transistor VT3; we connect the output from the base to probe X1. Let's see what happened on the board:

And finally we install the last few parts. Let's install the power switch, connecting it to the power plus with a path from one patch and to the VT2 emitter, with a path from the other patch connected to the switch. We connect this switch terminal with resistor R3, and connect the second patch of the resistor to the contacts of probe X2.

The essence of printed wiring is the formation of thin electrically conductive coatings on an insulating base, which perform the functions of installation wires and circuit elements - resistors, capacitors, inductors, contact parts, etc.

Below are the main terms used to describe the Documentation.

Printed conductor- a section of a conductive coating applied to an insulating base, performing the functions of a regular installation wire.

Printed Editing - a system of printed conductors that provide electrical connection of circuit elements.

PCB - insulating base with printed wiring applied on it.

Hanging elements- volumetric electrical and radio elements installed and fixed on a printed circuit board and having electrical contact with printed conductors.

Contact pad- a metallized area around the mounting hole, which has electrical contact with the printed conductor and provides electrical connection of the suspended circuit elements with the printed circuit.

Mounting hole- a hole in the printed circuit board intended for securing the leads of the hinged elements and their electrical connection with the printed conductors.

Grid- a grid applied to the image of the board and used to determine the position of mounting holes, printed conductors and other elements of the board.

Grid pitch- the distance between adjacent grid lines. The grid pitch must be a multiple of 0.625 mm (0.625; 1.25; 1.875; 2.5, etc.).

Grid node- point of intersection of grid lines.

Available seats - areas of the printed circuit board where, when placing conductors, the recommended values ​​for the width of conductors and the distance between conductors and contact pads can be maintained.

Bottlenecks - areas of the printed circuit board where, when placing conductors, their width and the distances between them and the contact pads are less than recommended (down to the minimum permissible).

Printing block - a printed circuit board with a printed circuit, attachments and other parts that has gone through all stages of manufacturing.

Design documentation for printed circuit boards and blocks is drawn up in accordance with the requirements of GOST 2.109-73, GOST 2.417-91 and current regulatory and technical documents. A single-sided or double-sided PCB drawing is classified as a part drawing. The drawing of the printed circuit board must contain all the information necessary for its manufacture and control: an image of the printed circuit board from the printed circuit board side; dimensions, maximum deviations and surface roughness of the printed circuit board and all its elements (holes, conductors), as well as the dimensions of the distances between them; necessary technical requirements; information about the material.

The dimensions of each side of the printed circuit board must be a multiple of 2.5 for a length of up to 100 mm, 5 for a length of up to 350 mm, 20 for a length of more than 350 mm. Maximum size any side of the printed circuit board should not exceed 470 mm. The ratio of the linear dimensions of the sides of the printed circuit board should be no more than 3:1 and is selected from the range 1:1; 1:2; 2:3; 2:5. The thickness of the boards is determined based on the mechanical requirements for the design of the printed circuit block, taking into account the manufacturing method. Recommended boards with a thickness of 0.8; 1.0; 1.5; 2.0; 2.5; 3.0 mm. Printed circuit board drawings are made in full size or with a magnification of 2:1, 4:1. 5:1. 10:1.

The development of a printed circuit board drawing begins with drawing grid coordinates. The main pitch of a rectangular coordinate grid according to GOST 10317-7 is taken to be 2.5 mm. For small-sized equipment and in technically justified cases, it is allowed to use additional steps of 1.25 and 0.5 mm.

The centers of all holes on the printed board must be located at a grid node. If this cannot be done due to the design features of the hinged element, then the center of the holes is located according to the instructions in the drawing for this element. This arrangement of hole centers is used for lamp panels, small-sized relays, connectors and other elements. In this case, the following requirements must be met: the center of one of the holes, taken as the main one, must be located in a coordinate grid node; the centers of the remaining holes should, if possible, be located on vertical or horizontal grid lines. In Fig. Figure 4.18 shows the location of the holes on the printed circuit board.

The diameters of mounting and adapter holes for metallized and non-metalized holes are selected from the range (0.2); 0.4; (0.5); 0.6; (0.7); 0.8; (0.9); 1, (1,2); 1.3; 1.5; 1.8; 2.0; 2.2; (2.4); (2.6)

(2.8); (3.0). Diameters not in brackets are preferred. It is not recommended to have more than three on one printed circuit board various diameters holes. The diameters of metallized holes are selected depending on the diameters of the leads of the hinged elements and the thickness of the board, and the diameters of non-metalized holes - depending on the diameters of the leads of the hinged elements installed in these holes (Table 4.1).

The need for countersinking of mounting and via holes is dictated by specific design requirements and the method of manufacturing the board.

When using other diameters of metallized holes in accordance with GOST 10317-79*, the difference between the diameter of the metallized hole and the diameter of the lead should be no more than 0.4 mm for leads with a diameter of 0.4 to 0.8 mm and 0.6 mm for leads with a diameter over 0 .8 mm.

The surface roughness of non-metallized mounting holes and ends of printed circuit boards must be Rz< 80 according to GOST 2789-73*. Surface roughness of mounting and transition metallized holes - Rz< 40.

To simplify the image of the board, the holes are shown in circles of the same diameter with the designation according to the table. 4.2.

When making holes in this way, a table of holes is placed on the drawing field (Fig. 4.19). Dimensions

the graph and form of the table are not established by GOST.

All mounting holes must have contact pads. The shape of the contact pad can be arbitrary, round, rectangular or close to them. The center of a symmetrically shaped pad must coincide with the center of the mounting hole; for rectangular and oval shaped pads, the center of the mounting hole can be shifted

(Fig. 4.20). Round pads and holes with countersinks are depicted as one circle, the diameter of which must correspond to the minimum size of the pad. The diameter of the contact pads should be indicated in the technical requirements of the drawing. If there are contact pads on the board of unspecified sizes or shapes other than round, it is allowed to depict all contact pads with a circle equal to the diameter of the hole. The shape and dimensions should be specified by writing in the technical requirements “The shape of the contact pads is arbitrary, i> mjn = = ...mm.”

To set the dimensions of group contact pads, it is recommended to display the image of the contact group on an enlarged scale with the required dimensions placed on the drawing field (Fig. 4.21). Recommended to do smooth transition contact pad into the conductor. In this case, the axis of symmetry of the printed conductor must be perpendicular to the tangent to the contour of the contact pad or the contour of the contact pad itself (Fig. 4.22). The distance from the edge of the conductor and the contact pad of the non-metalized hole to the edge of the board must be at least the thickness of the board T. Printed conductors should be depicted in the form of line segments coinciding with the lines of the coordinate grid or at an angle that is a multiple of 15°. Conductors of arbitrary configuration and rounding of conductor bends are allowed (Fig. 4.23).

Printed conductors should be made of the same width throughout. In narrow places, conductors are narrowed to the minimum permissible values ​​at the shortest possible length. The relative position of the conductors is not regulated. If it is necessary to lay conductors with a width of 0.3-0.4 mm along the entire length, it is recommended to provide for an expansion of the conductor such as a contact pad after 25-30 mm.

Conductors with a width of less than 2.5 mm are depicted with one line, which is the axis of symmetry of the conductor, more than 2.5 mm - with two lines and are hatched at an angle of 45° or blackened. Conductors with a width of more than 5 mm should be made as a screen (Fig. 4.24). The shape of the cutouts in wide conductors and screens should be shown in the drawing and determined by dimensions (see Fig. 4.21). In order to simplify the drawing, it is allowed to make conductors of any width in one line, while indicating the width of the conductor in the technical requirements of the drawing.

When laying printed conductors, conductor branches should be avoided if possible (Fig. 4.25); the ends of printed conductors intended for connecting a printed circuit are recommended to be placed with

Rice. 4.25. Examples of tracing printed conductors:

a - correct; b - incorrect

In Fig. Figure 4.29 shows an example of making a printed circuit board drawing using a combined method of dimensioning - using dimension and extension lines and a coordinate grid. The coordinate grid lines are drawn one at a time, and therefore a corresponding entry is given in the technical requirements of the drawing. A table of holes is made on the drawing field. All missing data regarding printed wiring are indicated in the technical requirements of the drawing.

An example of a printed circuit board drawing with dimensions indicated in the coordinate table is shown in Fig. 4.23. The diameters of the holes are indicated in the drawing, the relative location of the holes is in the coordinate table; all holes are marked with Arabic numerals in accordance with GOST 2.307-68*.

The printed circuit board drawing indicates overall dimensions boards, conductors having a strictly defined or variable width (in this case, the calculated width should be indicated at each section between two adjacent pads, vias or mounting holes), diameters and coordinates of fastening, technological and other holes not related to printed wiring.

The drawing field is indicatedboard manufacturing method, technical specifications (if not all data is contained in the drawing), grid pitch, width of conductors and distances between du them, the distances between the contact pads, between the contact pad and the conductor, tolerances for the execution of conductors, contact pads, holes and distances between du them, design features, technologies and other parameters of printed circuit boards.

Technical requirements are placed above the main inscription, formulated and presented in the following sequence:

1. Make a board using... method.

2. The board must comply with (GOST, OST).

3. Grid pitch... mm.

4. Maintain the configuration of the conductors according to the coordinate grid with a deviation from the drawing... mm.

5. Rounding of the corners of contact pads and conductors is allowed.

6. Places outlined by a dot-dotted line should not be occupied by conductors.

7. Requirements for the parameters of the board elements - in accordance with the design data.

8. Width of conductors in free places... mm, in narrow places... mm.

9. The distance between two conductors, between two contact pads or a conductor and a contact pad in free places... mm, in narrow places -... mm.

10. The shape of the contact pads is arbitrary.

11. It is allowed to lower the contact pads of metallized holes: on the outer layers to the countersink, on the inner layers...

12. Maximum deviations of the distances between the centers of holes, except as otherwise specified, in narrow places ± ... mm, in free places ± ... mm.

13. Maximum deviations of the distances between the centers of the contact pads in the group ± ... mm.

14. Mark with enamel... GOST..., font... according to GOST...

An example of recording technical requirements depending on the content of a printed circuit board drawing is shown in Fig. 4.23, 4.27, 4.29.

The features of printed wiring include: flat arrangement of printed conductors, which does not allow the transition from one board to another without jumpers, adapter blocks or connectors; installation of hanging elements and fastening of leads only by passing them into the holes; simultaneous soldering of all elements installed on the printed circuit board.

The hanging elements should be placed in correct rows, parallel to one another, on the side of the board where there are no printed conductors (Fig. 4.30). This arrangement allows you to install and secure attachments on automatic lines and perform immersion or wave soldering, eliminating the impact of solder on the attachments.

All attachments are attached to the board using leads, which are inserted into the mounting holes and bent. It is not recommended to place two or more leads in the mounting hole. Some elements, for example, low-power transistors, are attached with glue.

An assembly drawing of a printed circuit board, with a minimum number of images, should give a complete picture of the location and execution of all printed and mounted elements and parts. The assembly drawing is carried out in accordance with the requirements of GOST 2.109-73* taking into account the requirements of GOST 2.413-72*. The designs of the hinged elements are drawn in the form of simplified images, they are assigned an alphanumeric positional designation in accordance with the electrical circuit diagram according to which the electrical installation of the board is carried out (Fig. 4.31). The assembly drawing of the printed circuit board must indicate the item numbers of all components, overall and connecting dimensions, must contain information on methods of connecting hinged elements to the printed circuit board.

The technical requirements of the assembly drawing must contain references to documents (GOST, OST) that establish the rules for the preparation and fastening of hinged elements, information about solder, etc.

The main design document of the assembly drawing of a printed circuit board is a specification, drawn up in the form of a table according to the rules of GOST 2.106-96. When recording components that are elements of an electrical circuit diagram in the specification, in the “Note” column indicate the alphanumeric positional

designations of these elements (Fig. 4.32, 4.33).

The development of design documentation for printed circuit boards can be carried out manually, semi-automatically or automatically.

The manual method involves dividing hanging elements into functional groups, placing groups of elements on the board area, routing printed conductors and ensures optimal distribution of the conductive pattern.

At manual method design, a board drawing is developed containing an image of the board with a conductive pattern and holes, as well as, if necessary, an additional separate image of the part of the board that requires graphical explanation or sizing, a coordinate grid made in accordance with the requirements of GOST 2.417-91, the dimensions of all elements of the conductive pattern and their maximum deviations; technical requirements. The board drawing must be made on a scale of at least 2:1, maximum format A1.

Many people say that making your first PCB is very difficult, but in fact it is very simple.

Now I will tell you a couple of well-known ways to make a printed circuit board at home.

First, a short plan of how a printed circuit board is made:

1.Preparation for manufacturing
2. Conductive paths are drawn
2.1 Paint with varnish
2.2Draw with a marker or nitro paint
2.3Laser ironing
2.4Printing with film photoresist
3.Etching the board
3.1 Ferric chloride etching
3.2 Etching with copper sulfate and table salt
4. Tinning
5.Drilling

1. Preparation for PCB manufacturing

First, we need a sheet of foil PCB, metal scissors or a hacksaw, a regular pencil grater and acetone.

Carefully cut out the required piece of foil PCB. Then you need to carefully clean our textolite, from the copper side, with a pencil grater until it shines, then wipe our workpiece with acetone (this is done for degreasing).

Fig 1. Here is my blank

Everything is ready, now do not touch the shiny side, otherwise you will have to degrease again.

2. Draw conductive paths

These are the paths along which the current will be carried.

2.1 We draw the paths with varnish.

This method is the oldest and simplest. We will need the simplest nail polish.

Carefully draw conductive paths with nail polish. Be careful as the varnish sometimes bleeds and the tracks merge. Let the varnish dry. That's it.

Fig 2. Paths painted with varnish

2.2 Draw tracks with nitro paint or marker

This method is no different from the previous one, only everything is drawn much easier and faster

Fig 3. Paths painted with nitro paint

2.3 Laser ironing

Laser ironing is one of the most common ways to produce printed circuit boards. The method is not labor intensive and takes little time. I have not personally tried this method, but many people I know use it with great success.

First, we need to print a drawing of our printed circuit board on a laser printer. If not laser printer, you can print it on an inkjet and then make copies on a photocopier. To draw up drawings, I use the Sprint-Layout 4.0 program. Just be careful when printing using a mirror; many have killed boards this way more than once.

We will print on some old unnecessary magazine with glossy paper. Before printing, set your printer to the maximum toner consumption, this will save you from many problems.

Figure 4. Printing a drawing on glossy magazine paper

Now we carefully cut out our drawing in the form of an envelope.

Fig 5. Envelope with diagram

Now we put our blank into the envelope and carefully seal it at the back with tape. We seal it so that the textolite does not move in the envelope

Fig 6. Finished envelope

Now let's iron the envelope. We try not to miss a single millimeter. The quality of the board depends on this

Fig 7. Ironing the board

When ironing is complete, carefully place the envelope in a bowl of warm water.

Fig 8. Soaking the envelope

When the envelope is soaked, roll up the paper without any sudden movements, so as not to damage the toner tracks. If there are defects, take a CD or DVD marker and correct the tracks.

Fig 9. Almost finished board

2.4 Manufacturing a printed circuit board using film photoresist

As in the previous method, we make a drawing using the Sprint-Layout 4.0 program and press print. We will print on a special film for printing on inkjet printers. Therefore, we set up the print: We remove sides f1, m1, m2; In the options, check the Negative and Frame boxes.

Figure 10. Printing settings

We set the printer to print in black and white and set the color settings to maximum intensity.

Figure 11. Printer setup

We print on the matte side. This side is the working side, you can determine it by sticking it to your fingers.

After printing, let our template dry.

Fig 12. Drying our template

Now we cut off the piece of photoresist film we need

Figure 13. Photoresist film

Carefully remove protective film(it’s matte), glue it to our PCB blank

Figure 14. Gluing photoresist to the textolite

You need to glue it carefully, and remember, the better you press the photoresist, the better quality the tracks on the board will be. This is approximately what should happen.

Figure 15. Photoresist on PCB

Now, from the film on which we printed, we cut out our drawing and apply it to our photoresist with textolite. Don't mix up the sides or you'll end up with a mirror. And cover it with glass

Fig 16. Apply a film with a drawing and cover it with glass

Now let's take ultraviolet lamp and light up our paths. Each lamp has its own parameters for development. Therefore, choose the distance to the board and the glow time yourself

Fig 17. Illuminate the tracks with an ultraviolet lamp

When the tracks are illuminated, we take a small plastic dish, make a solution of 250 grams of water, a spoonful of soda, and lower our board into it without our board template and a second transparent photoresist film.

Fig 18. Place the board in a soda solution

After 30 seconds, our print of the tracks appears. When the photoresist is finished dissolving, we will get our board, which is what we wanted. Rinse thoroughly under running water. Everything is ready

Figure 19. Finished board

3. Etching of a new printed circuit board. Etching is a way to remove excess copper from PCB.

For etching, special solutions are used, which are made in plastic containers.

After making the solution, the printed circuit board is lowered there and etched for a certain time. You can speed up the etching time by maintaining the solution temperature around 50-60 degrees and constant stirring.

Remember to use rubber gloves when working and then wash your hands well with soap and water.

After etching the board, you need to rinse the board thoroughly under water and remove any remaining varnish (paint, photoresist) with regular acetone or nail polish remover.

Now a little about solutions

3.1 Ferric chloride etching

One of the most famous etching methods. For etching, ferric chloride and water are used in a ratio of 1:4. Where 1 is ferric chloride, 4 is water.

It’s easy to prepare: pour the required amount of chlorinated iron into a bowl and fill it with warm water. The solution should turn out green.

Etching time for a board measuring 3x4 centimeters is around 15 minutes

You can get ferric chloride at the market or in radio electronics stores.

3.2 Etching with copper sulfate

This method is not as common as the previous one, but it is also common. I personally use this method. This method is much cheaper than the previous one, and it’s easier to get the components.

Pour 3 tablespoons of table salt, 1 spoon of copper sulfate into the dishes and fill with 250 grams of water at a temperature of 70 degrees. If everything is correct, the solution should turn turquoise, and a little later green. To speed up the process, you need to stir the solution.

Etching time for a board measuring 3x4 centimeters is around one hour

You can get copper sulfate in agricultural supply stores. Copper sulfate is a blue fertilizer. It is in the form of crystal powder. Battery protection device from complete discharge

Hello dear visitor. I know why you are reading this article. Yes, yes I know. No, what are you? I'm not a telepath, I just know why you ended up on this page. Surely......

And again, my friend Vyacheslav (SAXON_1996) wants to share his work on speakers. Word to Vyacheslav I somehow got one 10MAC speaker with a filter and a high-frequency speaker. I haven’t…… for a long time.

Basic rules for board development

It is most convenient to design printed circuit boards in a 1:1 scale on graph paper or other material on which a grid is applied in 5 mm increments (for example, on a notebook sheet). It is advisable to place all holes for pins of parts in the printed circuit board in grid nodes, which corresponds to the pitch
2.5mm on a real board. The terminals of most microcircuits in a plastic case, many transistors and other radio components are located with this pitch. Less
The distance between holes should be chosen only in cases where it is absolutely necessary.
First you need to roughly arrange the parts. First of all, draw points for the pins of the microcircuit, then place small elements - resistors, capacitors,
and then the big ones - relays, etc. Their placement is usually related to the overall design of the device, determined by the size! existing building or free space in it. Often, especially
Especially when developing portable devices, the dimensions of the case are determined by the results of the printed circuit board layout. Sometimes it is necessary to redo the pattern of printed circuit wires
nicks several times to get the desired result of minification and functionality.
If your homemade product has no more than five microcircuits, you can usually place all printed conductors on one side of the board and make do with a small number of test leads.
jumpers soldered on the parts side.

Attempts to produce a single-sided printed circuit board for more
digital chips lead to a sharp increase
labor-intensive wiring and an excessively large number of jumpers. In these
In some cases, it makes more sense to switch to a double-sided PCB.
We will call the side of the board where the
printed conductors, the side of the conductors, and the reverse -
side of the parts, even if on it together with the parts
Some of the conductors have been laid. A special case is presented by
boards in which both conductors and parts are located on
one side, and the parts are soldered to the conductors without
holes. Boards of this design are rarely used.
The microcircuits are placed so that all connections on the board
were as short as possible, and the number of jumpers was
minimal. During the wiring of conductors, mutual
The placement of microcircuits has to be changed more than once.
Drawing of printed conductors of analog devices
any complexity can usually be placed on one
side of the board. Analog devices, working with
weak signals, and digital on high-speed
microcircuits (for example, KR531, KR1531, K500, KR1554 series)
Regardless of the frequency of their operation, it is advisable to collect
on boards with double-sided foil. Toy foil
sides of the board where the parts are located will play a role
common wire and screen. The foil of the common wire should not be
use as a conductor for high current,
for example, from the power supply rectifier, from the output
steps, from the dynamic head.

Next, you can begin the actual wiring. It is better to measure and write down the dimensions of the spaces occupied by the elements in advance. MLT-0.125 resistors are installed nearby, observing
the distance between their axes is 2.5 mm, and between the holes for
the terminals of one resistor are 10 mm. Places are also marked
% for alternating resistors MLT-0.125 and MLT-0.25 or
two MLT-0.25 resistors, if slightly bent during installation
one from the other (place three such resistors close to
the board will no longer succeed). With the same distances between
the pins and axes of the elements are installed by the majority
small-sized diodes and capacitors KM-5 and KM-6, up to
KM-66 with a capacity of 2.2 µF. “Thick” parts (more than 2.5 mm)
should be alternated with “thin” ones. Distance between
the contact pads of a particular part can be increased,
if necessary.
In this work it is convenient to use a small plate -
template made of fiberglass or other material, in
in which, in increments of 2.5 mm, holes with a diameter of
1-1.1 mm. On it you can apply the possible
arrangement of elements relative to each other.
If resistors, diodes and other parts with axial
pins should be placed perpendicular to the printed circuit board, you can
significantly reduce its area, however, the pattern of printed
conductors will become more complicated. When wiring you should take into account
restrictions on the number of conductors that fit between
contact pads intended for soldering
terminals of radioelements. For most parts diameter
The holes for the leads can be 0.8 mm. Restrictions
per number of conductors for typical layout options
contact pads with holes of this diameter
are shown in Fig. 8.1 (grid corresponds to 2.5 mm pitch on the board).
Between the contact pads of the holes with
with a center-to-center distance of 2.5 mm, guide the conductor almost
it is forbidden. However, if one or both holes have such
there is no pad (for example, at unused pins
microcircuits), this can be done (see Fig. 8.1 - top center).
It is quite possible to lay a conductor between the contact
platform and the edge of the board, through which at a distance
2.5 mm passes through the center of this area (see Fig. 8.1 - right).

Microcircuits whose pins are located in
body planes (series 133, K134, etc.)" can be mounted,
providing for this purpose the appropriate foil
contact pads with a pitch of 1.25 mm, but this is noticeable
complicates both wiring and board manufacturing. More expedient
alternate soldering of microcircuit pins to rectangular ones
platforms from the parts side and to the round platforms through
holes - on the opposite side (Fig. 8.2 -
The width of the microcircuit pins is not shown to scale). Pay
here it is two-sided.

Similar microcircuits with long leads
(e.g. 100 series), can be mounted in the same way as
plastic, bending the leads and passing them into the holes
fees. In this case, the contact pads are located in
in a checkerboard pattern (Fig. 8.3).

When designing a double-sided board, you should try to leave as few connections as possible on the parts side. This will make it easier to correct possible errors, set up the device and, if necessary, upgrade it. A common wire and a power wire are laid under the microcircuit housings, but they need to be connected only to the power pins of the microcircuits. Conductors to the inputs of microcircuits connected to the power circuit or the common wire are laid on the side of the conductors, and so that they can be easily cut when setting up or improving the device. If the device is so complex that signal circuit conductors have to be laid on the component side, make sure that any of them is accessible for connection to it and cutting. When developing amateur radio double-sided printed circuit boards, one should strive to avoid special jumpers between the sides of the board, using for this purpose the contact pads of the corresponding pins of the mounted parts. In these cases, the leads are soldered on both sides of the board. On complex boards, it is sometimes convenient to solder some parts directly to the printed circuit conductors. When a continuous layer of foil is used as a common wire, the holes for terminals that are not connected to this wire should be countersunk from the parts side. Typically, a unit assembled on a printed circuit board is connected to other units of the device using flexible conductors. In order not to damage the printed conductors during repeated soldering, it is advisable to make contact stands on the board at the connection points (it is convenient to use pin contacts with a diameter of 1 and 1.5 mm). The racks are inserted into holes drilled exactly to the diameter and soldered. On a double-sided PCB, the soldering pads for each stand must be on both sides. It is convenient to carry out preliminary wiring of conductors with a soft pencil on a sheet of smooth paper. The side of the printed conductors is drawn with solid lines, the reverse side - with dashed lines, so as not to get confused. Upon completion of the layout and adjustment of the drawing, place carbon paper under it with the ink layer facing up and use a red or green ballpoint pen to trace the contours of the board, as well as the conductors and holes related to the side of the parts. As a result, on the back of the sheet you will get a drawing of conductors for the side of the parts. Next, you should cut out a blank of the appropriate size from the foil material and mark it with a caliper using a grid with a pitch of 2.5 mm. By the way, it is convenient to choose the dimensions of the board in multiples of 2.5 mm. - in this case, you can mark it on four sides. If the board must have any cutouts, they are made after marking. The double-sided board is marked on the side where there are more conductors. After this, use a felt-tip pen to mark the centers of all the holes “in cells,” prick them with an awl and drill all the holes with a drill with a diameter of 0.8 mm. To drill circuit boards, it is convenient to use a homemade miniature electric drill, which can be bought on the radio market. Conventional steel drills become dull quite quickly when processing fiberglass; sharpen them with a small fine-grained whetstone without removing the drill from the chuck. After drilling the board, burrs are removed from the edges of the holes with a larger diameter drill or a fine-grained stone. The board is degreased by wiping with a cloth moistened with alcohol or acetone, after which, focusing on the position of the holes, a pattern of printed conductors is transferred to it using nitro paint in accordance with the drawing. A glass drawing pen is usually used for this, but it is better to make a simple homemade drawing tool. To the end of the broken student's pen, solder an injection needle shortened to 10-15 mm with a diameter of 0.8 mm. The working part of the needle must be sanded with fine-grained sandpaper. Nitro paint is poured into the funnel of the instrument in drops and, carefully taking it into the lips, blow lightly so that the paint passes through the needle channel. After this, you just need to make sure that the funnel is at least half filled with paint. The required paint density is determined experimentally by the quality of the lines drawn. If necessary, it is diluted with acetone or solvent 647. If it is necessary to make the paint thicker, it is left for some time in an open container. First of all, the contact pads are drawn, then connections are made between them, starting from those areas where the conductors are closely located. After the drawing is basically ready, you should, if possible, expand the common wire and power conductors, which will reduce their resistance and inductance, and therefore increase the stability of the device. It is also advisable to increase the contact pads, especially those to which racks and large parts will be soldered. To protect large surfaces of the foil from the etching solution, they are sealed with any adhesive film. If you make a mistake when applying a drawing, do not rush to correct everything right away - lay the correct one over the incorrectly applied conductor, and remove the excess paint when finally correcting the drawing (this is done before the paint has dried). Using a sharp scalpel or razor, the area to be removed is cut along the borders, after which it is scraped out. There is no need to specially dry the nitro paint after applying the design. While you are fixing the board, wash the tool - the paint will dry.

To obtain the conductors after applying the design to the foil, the board must be etched. The main material for etching is a solution of ferric chloride. To obtain it, you need to pour about 3/4 of ferric chloride powder into a glass and fill it with warm water. For etching, use a glass or plastic container, such as a photographic cuvette. Place the board in the solution with the pattern facing up so that the entire surface of the board is covered with the solution. The etching process is accelerated if the vessel is shaken or heated. Pickling produces toxic fumes, so work either in a well-ventilated area or outdoors. Periodically check the condition of the board by lifting it for inspection with wooden or plastic sticks - metal tools and devices cannot be used for this purpose. Once you are sure that the foil in unprotected areas has completely disappeared, stop the etching process. Transfer the board, for example using a clothespin, under running water and rinse thoroughly, then dry it at room temperature. If you intend to reuse the solution, pour it into a tightly sealed container and store it in a cool, dark place. Please note that the effectiveness of the solution decreases with repeated use. When working with ferric chloride solution, remember that it should not get on your hands or other exposed parts of the body, as well as on the surfaces of bathtubs and sinks, since the latter may leave yellow stains that are difficult to wash off. A solution of ferric chloride can be made in another way: treat iron filings with hydrochloric acid. Take 25 parts by weight of 10 percent hydrochloric acid and mix with one part by weight of iron filings. Keep the mixture in a tightly sealed container in a dark place for 5 days. When pouring the solution into a vessel for etching, do not shake it: the sediment should remain in the container in which the solution was prepared. The duration of the board etching process in a ferric chloride solution is usually 40-50 minutes and depends on the concentration of the solution, its temperature, and the thickness of the foil. Solutions for etching boards can be prepared not only based on ferric chloride. For many radio amateurs, an aqueous solution of copper sulfate and table salt may be more accessible. It is not difficult to prepare - dissolve 4 tablespoons of table salt and 2 tablespoons of copper sulfate crushed into powder in 500 ml of hot water (temperature about 80 °C). The effectiveness of the solution increases if it is kept for 2-3 weeks. The etching time of the board in such a solution is three hours or more. A significant reduction in the etching period can be achieved by using acid-based solutions. The process of etching the board, for example, in a concentrated solution of nitric acid, lasts only 5-7 minutes. After etching, wash the board thoroughly with soap and water. Good results are obtained by using a solution of hydrochloric acid and hydrogen peroxide. To prepare it, take 20 parts (by volume) of hydrochloric acid with a density of 1.19 g/cm3, 40 parts of pharmaceutical hydrogen peroxide and 40 parts of water. First mix water with hydrogen peroxide, then carefully add the acid. In this case, the drawing is done with nitro paint. Pour acid-based solutions into glass or ceramic containers; work with them only in well-ventilated areas. Of interest is the method of galvanic etching of boards. To do this, you will need a DC source with a voltage of 25-30 V and a concentrated solution of table salt. Using an alligator clip, connect the positive pole of the source to the unpainted areas of the board's foil, and attach it to the exposed and looped end of the wire coming from the negative pole of the source cotton swab, abundantly soaked in salt solution. Move it along the surface of the board, lightly pressing it against the foil. The movement of the tampon should resemble the drawing of the number 8. In this case, the foil will be “washed off,” as it were. Change the cotton whenever it gets dirty.

Radio amateurs advise

Professional radio amateurs offer us the ability to make printed circuit boards quite quickly using a laser printer (or copier), an iron and film from Techniks or DynaArt (everything else - foil PCB, ferric chloride, drills - as usual). Film and iron are needed to transfer the printed circuit board design onto the copper. Having prepared a drawing of a printed circuit board using any package for developing printed circuit boards or some editor for drawing pictures, we make a test print. Output to blank slate PCB image. Then we cut out a fragment from the film with a margin of about 1 cm on each side. Glue it with tape with the glossy side to the paper on top of the drawing. We insert the sheet of film into the printer and print again. We get a film with an image of a printed circuit board printed on it. Then we prepare the textolite. In my opinion, the Surzha cleaning agent is excellent for this (do not neglect basic safety standards - use rubber gloves). After washing and drying the board, apply a film of toner to it and iron it with an iron for 1.5-4 minutes at a temperature of 135-160 °C. When the board cools down, carefully remove the film under running water - the drawing is transferred. We inspect the board and, if there are any flaws, correct them with an alcohol marker. Now you can etch using a ferric chloride solution. You can clean the toner from the finished board with an old blade, using it as a scraper. The same method is suitable for the production of double-sided printed circuit boards. To combine layers, you can use the following trick: draw three anchor points on both layers in the same place - best along the perimeter of the board. After transferring the first layer, drill holes at these points. We combine the points on the film for the second side with the holes. This option is not suitable for Techniks film, since it is opaque. You can do this: add 4 parallel lines to the printed circuit board drawing in both layers at a distance of 5 mm from the board border. After transferring the first layer, apply a ruler over the line and extend it to the end of the workpiece. We make marks on the ends of the workpiece and transfer the lines to the other side of the board. The second film is combined with the lines - you can transfer the second layer. The quality of these boards is very good. There is a technology for manufacturing printed circuit boards using ordinary drawing tracing paper. It differs little from the technology with special film. Before use, the tracing paper must be passed through the printer or ironed to remove heat shrinkage. Then everything is the same. After cooling, place the board with toner and tracing paper in warm water, wait until the tracing paper gets wet, and carefully roll up the paper with a cloth. After this we correct it with a marker. It should be noted that the quality of the boards is somewhat worse, but much cheaper. To apply a design to the board, you can also use an alcohol marker (preferably German), but this is only suitable for simple boards in a single copy. The quality is the same as with tracing paper, but the difficulties are immeasurably greater. But for simple things it will do.

Layout of radio components on the board

The article discusses the topology high frequency boards from a practical point of view. Its main goal is to help beginners get a feel for the many points that must be taken into account when developing printed circuit boards (PCBs) for high-frequency devices. It will also be useful for improving the skills of those specialists who had a break in board development. The main attention is paid to ways to improve the characteristics of circuits, speeding up the time of their development and changes.

The issues considered and the proposed techniques are applicable to the topology of high-frequency circuits in general. When operational amplifier(OU) works on high frequencies, the main characteristics of the circuit depend on the PCB topology. Even with good design, circuit performance can be mediocre due to a poorly designed or sloppy circuit board. You can be sure that the diagram will show the calculated parameters only by thinking in advance and paying attention to the main points during the entire process of developing the PCB topology.

Scheme

A good circuit is a necessary but not sufficient condition for a good topology. When designing it, you should not skimp on additional information in the drawing, and carefully monitor the direction of the signal. Keeping the signal flowing from left to right will most likely have the same effect on the PCB. Maximum useful information in the scheme will provide optimal performance developers, technicians, engineers who will be very grateful to you, and customers will not have to urgently look for a developer in case of any difficulties.

What information, besides the usual designations, power dissipation and tolerances, should be included on the circuit? Here are some tips on how to make a super circuit from a regular circuit: add waveforms, mechanical information about the packages or dimensions, specify the length of the tracks, areas where parts cannot be placed, parts that should be on the top side of the PCB; add setup instructions, element rating ranges, thermal information, matched impedance lines, brief definitions circuit operation and so on.

Don't trust anyone

If you're not a layout designer yourself, take the time to walk through the layout with the layout designer. It is much easier and faster to pay attention to the topology at the beginning than to deal with endless modifications later. Don't expect the layout designer to be able to read your mind. Introductory notes and guidance are most important at the beginning of the board layout process. The more information and participation in the wiring process, the better the board will turn out. Indicate to the developer the intermediate steps at which you want to become familiar with the wiring process. These " control points» protect the board from advanced errors and minimize topology corrections.

Directions to the developer should include: brief description circuit functions; a sketch of the board showing the locations of the inputs and outputs; design (stack up) of the board (i.e. board thickness, number of layers, details of signal layers and solid layers - power, ground - analog, digital, high-frequency); signals that should be on each layer; placement of critical elements; precise placement of decoupling elements; critical tracks; impedance matched lines; paths of the same length; element sizes; paths far (or close) from each other; the chains are closer (or further) apart; elements close (or far) from each other; elements on the top and bottom of the board. No one will accuse you of too much information; if there is too little, they will complain; on the contrary, they will never.

Location, location and location again

When placing a circuit on a board, everything is important: from the layout individual elements before choosing which circuits should be located nearby.

Typically the location of the inputs, outputs and power is determined. Particular attention should be paid to topology: the location of critical elements - both individual circuits and the circuit as a whole. Determining the location of key components and signal paths from the very beginning ensures that the circuit will perform as expected. This allows you to reduce costs, solve problems and reduce wiring time.

Power supply decoupling

Decoupling the power supply from the amplifier's power pins to minimize noise is a critical aspect of the PCB design process—for both high-speed op-amp designs and other high-frequency circuits. Typically, one of two configurations is used to decouple high-speed op amps.

Between power bus and ground

This method works better in most cases and allows you to use capacitors connected in parallel from the op amp's power pins directly to ground. Usually two are sufficient, but some circuits benefit from several capacitors connected in parallel.

Parallel connection of capacitors with different capacitances ensures that there will be a low impedance at the power terminals alternating current over a wide frequency range. This is especially important when the power supply instability factor (PSR) drops - the capacitors compensate the amplifier for this decrease. Providing a low impedance path to ground for many decades of frequency prevents unwanted noise from entering the op amp. In Fig. 1 shows the advantages of this method. At lower frequencies, capacitors with large capacity have low circuit resistance to ground. At the self-resonant frequency of the capacitor, the quality of the capacitor deteriorates and it becomes an inductance. Therefore, it is important to use many capacitors: when frequency response one falls, the other becomes significant, providing low AC impedance over a range of many decades of frequency.

Rice. 1. Dependence of capacitor impedance on frequency

Directly near the op-amp's power pins, a capacitor with a lower capacitance and smaller geometric dimensions should be placed on the same side as the op-amp - and as close to the amplifier as possible. The ground side of the capacitor must be connected to the ground plane with minimum lead and trace lengths. The connection should be as close to the amplifier load as possible to minimize interference between the power rails and ground. Rice. 2 illustrates this technique.

Rice. 2. Connecting power buses to ground with parallel capacitors

This process should be repeated with the next largest capacitor. A good rule of thumb is to start with the smallest 0.01uF capacitor and work your way up to a 2.2uF oxide capacitor with a low ESR (equivalent series resistance). The first one listed in case 0508 has a small series inductance and excellent high-frequency parameters.

Between one bus and another

An alternative configuration is to use one or more capacitors connected between the positive and negative power rails of the op amp. This method is used when it is difficult to fit all four capacitors into the circuit. The disadvantage is that the capacitors are larger because the voltage across them is doubled compared to blocking each source individually. In this case, a capacitor with a high breakdown voltage is required, which leads to an increase in its size. However, this option improves both PSR and distortion performance.

Since each circuit and its topology are different, the configuration, number and capacitance of capacitors will be determined by the specific requirements of the circuit.

Where C- capacity; A- lining area in cm²; k- relative dielectric constant of the board material; And d- distance between plates in cm.

Rice. 5. Capacitance of a plane-parallel capacitor

You should also consider the inductance of the conductor strip, which arises from excessive trace length and insufficient ground layer. Equation 2 gives the track inductance formula (Figure 6):

Where W- track width; L- its length; And H- thickness. All dimensions are in millimeters.

Rice. 6. Track inductance

Rice. 7. Response to an impulse without a layer and with a ground layer

Where T- board thickness and d- diameter of the via hole in centimeters.

Rice. 8. Via dimensions

layer of earth

Here we will touch on some key points of this issue. List of links to this topic is given at the end of the article.

Since the earth layer usually has a large area and cross-section, its resistance is kept minimal. On low frequencies current flows along the path of least resistance, but at high frequencies it follows the path of least resistance. However, there are exceptions, and sometimes a smaller ground plane works better. This also applies to high-speed op-amps if you remove some of the ground under the input and output pads.

Analog and digital circuits, including their grounds and substrates, should be separated whenever possible. Steep pulse rises create current peaks that flow through the ground layer and create noise, degrading the analog performance of the circuit.

At high frequencies, you should pay attention to a phenomenon called the skin effect. It forces current to flow along the outer surface of the conductor, as if making it narrower and increasing the resistance compared to the value of the conductor at direct current. Although consideration of the skin effect is beyond the scope of this article, here is an approximate expression for calculating the skin depth in copper (in cm):

To reduce the skin effect, a coating of metals that reduce the possibility of its occurrence may be useful.

Housings

Rice. 9. Differences in the topology of circuits with op-amps: a) SOIC package; b) SOT-23 housing; c) SOIC package with RF resistor on the bottom side of the board.

The topology of the board with the SOT-23 package is almost ideal: minimal track length feedback, minimal use of vias; the load and decoupling capacitor are connected to ground by short paths to one point; positive voltage decoupling capacitor, not shown in Fig. 9b, placed directly under the negative voltage capacitor on the bottom side of the board.

Low distortion amplifier pinout

New distortion-reducing pinouts found in some Analog Devices op amps (such as the AD8045) help eliminate both of these problems and improve performance in two other important areas. The low distortion LFCP pinout shown in Fig. 10, is obtained from a traditional op-amp pinout, rotating it counterclockwise by one pin and adding a second output pin intended for the feedback circuit.

Rice. 10. Op-amp with pinout for low distortion

The low-distortion pinout allows a short connection between the output (feedback pin) and the inverting input, as shown in Fig. 11. This greatly simplifies the topology and gives it a rational form.

Rice. 11. PCB topology for AD8045 low distortion op amp

The second advantage of the housing is the attenuation of the second harmonic nonlinear distortion. One of the reasons for its occurrence is the connection between the non-inverting input and the negative supply voltage output. The low-distortion pinout of the LFCP package eliminates this coupling and significantly attenuates the second harmonic; in some cases its reduction can be up to 14 dB. In Fig. Figure 12 shows the difference in distortion between the AD8099 op amp in a SOIC package and in an LFCSP package.

Rice. 12. Comparison of AD8099 op-amp distortion in different packages - SOIC and LFCSP

This case has another advantage - power dissipation. The package has an exposed chip substrate, which reduces its thermal resistance, improving θ JA by about 40%. In this case, the chip operates at lower temperatures, which increases its reliability.

Three high-speed Analog Devices op amps are now available in new low-distortion packages: the AD8045, AD8099, and AD8000.

Wiring and shielding

On printed circuit boards electronic circuits most can be present at the same time various signals- analog and digital, with high and low voltage, high and low current - from direct current to gigahertz frequencies. Keeping them from interfering with each other is a difficult task.

It's important to think ahead about your board's signal handling plan, note which ones are sensitive, and determine steps to keep them intact. Layers of the earth, in addition to providing a reference potential for electrical signals, can also be used for shielding. When you want to isolate signals, the first step is to ensure there is sufficient distance between signal traces. Let's look at a few practical measures:

• Minimizing the length of parallel lines and preventing close proximity between signal traces on the same layer will reduce inductive coupling.
• Minimizing trace lengths on adjacent layers will prevent capacitive coupling.
• Signal paths that require special insulation must be routed on different layers and, if it is impossible to space them further, perpendicular to each other, a layer of earth should be laid between them. Perpendicular routing minimizes capacitive coupling and the ground forms an electrical shield. This technique is used to form lines with matched impedance (characteristic impedance).

High frequency (RF) signals are typically carried along impedance-matched lines. That is, the characteristic impedance of the track is ensured to be equal to, for example, 50 Ohms (typical for RF circuits). The two commonly used types of matched lines, microstrip and stripline, can produce the same results, but have different implementations.

The microstrip matched line shown in Fig. 13, can run on either side of the board; it uses the layer of earth immediately underneath it as a base ground plane.

Rice. 13. Microstrip transmission line

To calculate the characteristic wave resistance line on the FR4 board, you can use the following formula:

Where H- distance from the ground plane to the track; W- track width; T- track thickness; All dimensions are in mils (1 mil = 10 -3 inches). ε r- relative dielectric constant of the board material.

A stripline matched line (Figure 14) uses two ground plane layers and a signal trace between them. This method uses more traces, requires more layers, is sensitive to changes in insulator thickness, and is more expensive, so it is usually used only in applications with higher requirements.

Rice. 14. Stripline matched line

The equation for calculating the characteristic impedance of a strip line is:

Rice. 15. Protective rings: a) inverting and non-inverting circuit; b) implementation of both options in the SOT-23-5 package

There are many other shielding and wiring options. For further information on these and other topics mentioned above, the reader is encouraged to consult the links below.

Conclusion

For successful design of devices using high-speed op-amps, a reasonable PCB topology is important. The foundation is a good design, and close collaboration between the circuit engineer and the PCB designer is also important, especially when placing and connecting components.

Literature

1. Ardizzoni J. Keep High-Speed ​​Circuit-Board Layout on Track // EE Times, May 23, 2005.
2. Brokaw P. An IC Amplifier User's Guide to Decoupling, Grounding, and Making Things Go Right for a Change // Analog Devices Application Note AN-202.
3. Brokaw P., Barrow J. Grounding for Low- and High-Frequency Circuits // Analog Devices Application Note AN-345.
4. Buxton J. Careful Design Tames High-Speed ​​Op Amps // Analog Devices Application Note AN-257.
5. DiSanto G. Proper PC-Board Layout Improves Dynamic Range // EDN, November 11, 2004.
6. Grant D., Wurcer S. Avoiding Passive-Component Pitfalls // Analog Devices Application Note AN-348.
7. Johnson H. W., Graham M. High-Speed ​​Digital Design, a Handbook of Black Magic. Prentice Hall, 1993.
8. Jung W., ed., Op Amp Applications Handbook // Elsevier-Newnes, 2005.