In PCB board design, it is necessary to comprehensively consider the size of the PCB board, pass the current, and select an appropriate line width. PCB copy board, the industry is also often called circuit board copy board, circuit board clone, circuit board duplication, PCB clone, PCB reverse design or PCB reverse research and development.
That is, on the premise that there are already physical electronic products and circuit boards, reverse analysis of the circuit board is carried out by means of reverse research and development technology, and technical documents such as the PCB file, bill of materials (BOM) file, and schematic file of the original product and PCB silk screen production files are restored 1:1.
Then use these technical documents and production documents to carry out PCB board making, component welding, flying probe testing, circuit board debugging, and complete the complete copy of the original circuit board model.
With the continuous development and deepening of the copy board industry, today's PCB copy board concept has been extended in a wider range, no longer limited to simple circuit board copying and cloning, but also involves the secondary development of products and the development of new products research and development.
Then, according to the file diagram or the real object, how to reverse the PCB schematic diagram, and what is the reverse process like? What details should be paid attention to?
reverse step
1. Record PCB related details
Get a PCB, first record the models, parameters, and positions of all components on paper, especially the direction of diodes, triodes, and IC notches. It is best to take two photos of the component location with a digital camera. Many pcb circuit boards are getting more and more advanced, and the diodes and triodes on it are not visible 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 into the scanner. The scanner needs to increase the scanning pixels slightly to get a clearer image.
Then lightly polish the top layer and the bottom layer with water gauze paper until the copper film is shiny, put it into 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 lightness of the canvas so that the contrast between the part with copper film and the part without copper film is strong, and then convert the next picture to black and white, check whether the lines are clear, if not, repeat this step. If it is clear, save the picture as black-and-white BMP format files TOP BMP and BOT BMP. If you find any problems with the graphics, you can use PHOTOSHOP to repair and correct them.
4. Verify the position coincidence of PAD and VIA
Convert the two BMP format files into PROTEL format files respectively, and transfer two layers into PROTEL. If the positions of the PAD and VIA after the two layers basically coincide, it shows that the previous steps are done well. If there is any deviation, then Repeat step three. Therefore, pcb copy board is a job that requires patience, because a little problem will affect the quality and matching degree after copying the board.
5. Drawing layer
Convert the BMP of the TOP layer to the TOP PCB, pay attention to the conversion to the SILK layer, which is the yellow layer, and then you just draw the line on the TOP layer, and place the device according to the drawing in the second step. Delete the SILK layer after drawing. Repeat until all layers are drawn.
6. Combination of TOP PCB and BOT PCB
Import the TOP PCB and BOT PCB in PROTEL, and it is OK to combine them into one picture.
7. Laser printing TOP LAYER, BOTTOM LAYER
Use a laser printer to print the TOP LAYER and BOTTOM LAYER on the transparent film (1:1 ratio), put the film on the PCB, and compare whether there is any error. If it is correct, you are done.
8. Test
Test whether the electronic technical performance of the copy board is the same as that of the original board. If it's the same then it's really done.
Attention to detail
1. Reasonable division of functional areas
When performing reverse design of a schematic diagram of a complete PCB circuit board, a reasonable division of functional areas can help engineers reduce unnecessary troubles and improve the efficiency of drawing.
Generally speaking, components with the same function on a PCB board will be arranged in a centralized manner, and dividing the area by function can provide a convenient and accurate basis for reverse derivation of 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 out the core components in a certain functional unit, and then find out other components of the same functional unit according to the wiring connection to form a functional partition.
The formation of functional partitions is the basis of schematic diagram drawing. In addition, in this process, don't forget to make good use of the serial numbers of components on the circuit board, which can help you perform functional partitioning faster.
2. Find the reference parts
This reference part can also be said to be the main component used at the beginning of the schematic diagram drawing. After the reference part is determined, drawing according to 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, which is convenient for drawing. Such as integrated circuits, transformers, transistors, etc., can be used as suitable reference parts.
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 layout knowledge, and so on. The distinction of these lines can be analyzed from the aspects of the connection of components, the width of the copper foil of the line, and the 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 lines, different lines of different colors can be used for various lines to ensure clear identification, special signs can be used for various components, and even Draw unit circuits separately and combine them at the end.
4. Master the basic framework and learn from similar schematic diagrams
Engineers need to be proficient in the frame composition and schematic drawing of some basic electronic circuits, not only to be able to directly draw the basic composition forms of some simple and classic unit circuits, but also to 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 a certain similarity in the schematic diagram. Engineers can make full use of similar circuit diagrams to reverse the new product schematic diagram based on the accumulation of experience.
5. Check and optimize
After the schematic drawing is completed, the reverse design of the PCB schematic diagram can only be said to be completed after testing and checking. The nominal value of components sensitive to PCB distribution parameters needs 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 is completely consistent with the document diagram.
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