PCB copying skills

Nowadays, many circuits are the same, so you can copy the circuit board. It is not difficult to copy the circuit board. The difficulty lies in copying. Today the author will tell you about the steps of reverse reasoning. Once you learn it, you can easily master PCB copying! In fact, many people do not understand PCB copying. Some people think that PCB copying is a copycat, which means imitation, but PCB copying Boards are definitely not imitations. The purpose of PCB copying is to learn the latest foreign electronic circuit design technology, then absorb excellent design solutions, and then use them to develop and design better products.

Without further ado, let’s take a look at the reverse derivation steps with the author!

1. Backward steps:

1. Record PCB related details

Get a PCB and first record the models, parameters, and locations of all components on paper, especially the directions of diodes, transistors, and IC gaps. It is best to take two photos of the component locations with a digital camera. Many PCB circuit boards are becoming more and more advanced. Some of the diodes and transistors on them cannot be seen at all if you don't pay attention.

2. Scanned image

Remove all components and remove the tin from the PAD holes. Clean the PCB with alcohol and put it into the scanner. When scanning, the scanner needs to slightly increase the scanning pixels in order to get a clearer image. Then use water gauze paper to lightly polish the top and bottom layers until the copper film shines. Put it in the scanner, start PHOTOSHOP, and scan in the two layers separately in color. Note that the PCB must be placed horizontally and vertically in the scanner, otherwise the scanned image will not be usable.

3. Adjust and correct the image

Adjust the contrast and lightness of the canvas so that the part with copper film and the part without copper film are in strong contrast. Then convert the image to black and white and check whether the lines are clear. If not, repeat this step. If it is clear, save the image as black and white BMP format files TOP BMP and BOT BMP. If you find problems with the image, you can use PHOTOSHOP to repair and correct it.

4. Verify the positional coincidence of PAD and VIA

Convert the two BMP format files to PROTEL format files respectively, and transfer the two layers in PROTEL. If the positions of PAD and VIA after the two layers basically coincide, it indicates that the first few steps have been done well. If there is a deviation, then Repeat step three. Therefore, PCB copying is a job that requires great patience, because any small problem will affect the quality and matching after copying.

5. Draw layer

Convert the BMP of the TOP layer to TOP PCB. Pay attention to convert it to the SILK layer, which is the yellow layer. Then you just trace the line on the TOP layer and place the device according to the drawing in the second step. After painting, delete the SILK layer. Repeat until all layers are drawn.

6.Picture of TOP PCB and BOT PCB

In PROTEL, import the TOP PCB and BOT PCB and merge them into one picture.

7. Laser printing TOP LAYER, BOTTOM LAYER

Use a laser printer to print the TOP LAYER and BOTTOM LAYER on transparent film respectively (1:1 ratio), put the film on the PCB, and compare whether there are errors. If they are correct, you are done.

8. Test

Test whether the electronic performance of the copied board is the same as the original board. If it's the same, it's really done.

2. Pay attention to details

1. Reasonably divide functional areas

When reverse designing the schematic diagram of a complete PCB circuit board, reasonable division of functional areas can help engineers reduce unnecessary troubles and improve drawing efficiency. Generally speaking, components with the same functions on a PCB board will be arranged centrally. Dividing areas by function can provide a convenient and accurate basis for inferring the schematic diagram. However, this division of functional areas is not arbitrary. It requires engineers to have a certain understanding of electronic circuit related knowledge. First, find the core components in a certain functional unit, and then follow the wiring connections to find other components of the same functional unit to form a functional partition.

The formation of functional partitions is the basis for schematic drawing. In addition, during this process, don’t forget to make clever use of the component serial numbers on the circuit board. They can help you partition functions faster.

2. Find the right reference parts

This reference part can also be said to be the main component PCB network city used at the beginning of drawing the schematic diagram. After determining the reference parts, drawing based on the pins of these reference parts can ensure the accuracy of the schematic diagram to a greater extent. sex. For engineers, the determination of reference parts is not a very complicated matter. Generally, components that play a major role in the circuit can be selected as reference parts. They are generally larger in size and have more pins, making it easier to draw. Such as integrated circuits, transformers, transistors, etc., can be used as suitable reference components.

3. Correctly distinguish lines and draw wiring reasonably

For the distinction between ground wires, power wires, and signal wires, engineers also need to have relevant power supply knowledge, circuit connection knowledge, PCB wiring knowledge, etc. The distinction between these lines can be analyzed from the aspects of component connection, line copper foil width, and characteristics of the electronic product itself. In wiring drawing, in order to avoid crossing and crossing of lines, a large number of grounding symbols can be used for ground wires. Different lines of different colors can be used to ensure clarity for various lines. Special signs can also be used for various components, and even Draw the unit circuits separately and finally combine them.

4. Master the basic framework and learn from similar schematics

Engineers need to be proficient in the framework composition and principle drawing methods of some basic electronic circuits. They must not only be able to directly draw the basic composition forms of some simple and classic unit circuits, but also be able to form the overall framework of electronic circuits. On the other hand, don't ignore that the same type of electronic products have certain similarities in schematic diagrams. Engineers can fully draw on similar circuit diagrams to infer new product schematics based on accumulated experience.

5. Check and optimize

After the schematic drawing is completed, the reverse design of the PCB schematic diagram is completed after testing and verification. The nominal values ​​of components that are sensitive to PCB distribution parameters need to be checked and optimized. According to the PCB file diagram, the schematic diagram is compared, analyzed and checked to ensure that the schematic diagram and the file diagram are completely consistent. The above are some techniques for copying boards, which also require daily accumulation.