How to reverse the PCB schematic diagram based on the file diagram or the physical object
In the design of the PCB board, it is necessary to comprehensively consider the size of the PCB board and select a suitable line width through the current. PCB copying is also often referred to as circuit board copying, circuit board cloning, circuit board replication, PCB cloning, PCB reverse design or PCB reverse research and development in the industry.
That is, on the premise that there are physical electronic products and physical circuit boards, reverse research and development technical means are used to reversely analyze the circuit board, and the PCB files, bill of materials (BOM) files, schematic files and other technical files of the original product and PCB silk screen production files are restored 1:1.
Then use these technical files and production files to perform PCB board making, component welding, flying probe testing, and circuit board debugging to complete the complete replication of the original circuit board sample.
With the continuous development and deepening of the copying industry, today’s PCB copying concept has been extended to a wider range, no longer limited to simple circuit board replication and cloning, but also involves product secondary development and new product research and development.
So, based on the file diagram or physical object, how to reverse the PCB schematic diagram, what is the reverse process like? What details should be paid attention to?
How to reverse the PCB schematic diagram based on the file diagram or the real object
Reverse steps
1.Record the relevant details of the PCB
Get a PCB, first record the model, parameters, and position of all components on paper, especially the direction of the diode, triode, and the direction of the IC notch. It is best to take two photos of the position of the components with a digital camera. Many PCB circuit boards are getting more and more advanced, and some diodes and triodes on them cannot be seen at all if you don’t pay attention.
2.Scanned image
Remove all components and remove the tin in the PAD hole. Clean the PCB with alcohol and then put it in the scanner. When scanning, the scanner needs to slightly increase the scanning pixels to get a clearer image.
Then use water gauze paper to lightly polish the top and bottom layers until the copper film is shiny, put it in the scanner, start PHOTOSHOP, and scan the two layers separately in color.
Note that the PCB must be placed horizontally and vertically in the scanner, otherwise the scanned image cannot be used.
3.Adjust and correct the image
Adjust the contrast and brightness of the canvas to make the part with copper film and the part without copper film have a strong contrast, then convert the secondary image to black and white, 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 that there is a problem with the graphics, you can use PHOTOSHOP to repair and correct it.
4.Check the position coincidence of PAD and VIA
Convert the two BMP format files into PROTEL format files respectively, and call two layers in PROTEL. If the positions of PAD and VIA of the two layers basically coincide, it means that the previous steps are done well. If there is a deviation, repeat the third step. Therefore, PCB copying is a very patient job, because a small problem will affect the quality and the matching degree after copying.
5.Drawing layer
Convert the BMP of the TOP layer to the TOP PCB, pay attention to converting to the SILK layer, which is the yellow layer, and then you draw lines on the TOP layer, and place the components according to the drawing in the second step. After drawing, delete the SILK layer. Repeat until all layers are drawn.
6.Combine TOP PCB and BOT PCB
In PROTEL, call in TOP PCB and BOT PCB and combine them into one picture.
7.Laser print TOP LAYER and BOTTOM LAYER
Use a laser printer to print TOP LAYER and BOTTOM LAYER on transparent film (1:1 ratio), put the film on the PCB, and compare whether there is any error. If there is no error, you are done.
8.Test
Test whether the electronic technical performance of the copy board is the same as the original board. If it is the same, it is really completed.
Pay attention to details 1. Reasonable division of functional areas
When reverse designing the schematic diagram of a complete PCB circuit board, reasonable division of functional areas can help engineers reduce some unnecessary troubles and improve drawing efficiency.
Generally speaking, components with the same function on a PCB board will be arranged together, and dividing the area by function can provide a convenient and accurate basis for reverse deducing the schematic diagram.
However, the division of this functional area is not random. It requires engineers to have a certain understanding of electronic circuit related knowledge.
First, find out the core components in a functional unit, and then follow the wiring connection 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, in this process, don’t forget to cleverly use the component numbers on the circuit board, which can help you perform functional partitions faster.
- 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 schematic drawing. After determining the reference parts, drawing according to the pins of these reference parts can ensure the accuracy of the schematic to a greater extent.
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, which is convenient for drawing. For example, integrated circuits, transformers, transistors, etc. can all be used as suitable reference parts.
- Correctly distinguish the lines and draw the wiring reasonably
For the distinction between ground wires, power lines, and signal lines, engineers also need to have relevant power knowledge, circuit connection knowledge, PCB wiring knowledge, etc. The distinction between these lines can be analyzed from the connection of components, the width of the copper foil of the lines, and the characteristics of the electronic products themselves.
In wiring drawing, in order to avoid crossing and interlacing of lines, a large number of grounding symbols can be used for ground wires, and different lines of different colors can be used for various lines to ensure clear identification. Special signs can also be used for various components, and even unit circuits can be drawn separately and then combined.
- Master the basic framework and learn from similar schematics
For the framework composition and schematic drawing of some basic electronic circuits, engineers need to master them proficiently. They should 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 the electronic circuit.
On the other hand, don’t ignore that the same type of electronic products have certain similarities in the schematic diagram. Engineers can use the same circuit diagram based on their experience and fully learn from the same circuit diagram to reverse the schematic diagram of new products.
- Verification and optimization
After the schematic diagram is drawn, it needs to go through the testing and verification phase before the reverse design of the PCB schematic diagram can be completed. The nominal values of components that are sensitive to PCB distribution parameters need to be verified and optimized. According to the PCB file diagram, the schematic diagram is compared, analyzed and verified to ensure that the schematic diagram and the file diagram are completely consistent.
