How To Reverse The PCB Schematic

With the continuous development and deepening of the board copying industry, today's PCB board copying concept has been a wider range of extension, not limited to the simple circuit board copy and cloning, but also involved in the secondary development of products and new product research and development., for example, through the analysis of both the product technical documents, design thinking, structure characteristics and technology of understanding and discussion, can provide the feasibility analysis for the research and development of new products and competitive information, to assist the research and design units timely follow up the latest technology development trends, timely adjustment to improve product design, research and development the most has the market competitive new products.

PCB copy board through the process of the part of the extraction and the technical data file modification, can realize quick update all kinds of electronic products upgrading and the secondary development, according to the principle of copy plate extraction file figure with figure, professional design personnel can also according to the customer's willingness to optimize the PCB design and change, also can on the basis of adding new functionality or for product features to redesign, this product will have a new function with the fastest speed and a new attitude, not only have their own intellectual property rights, and win the advantage in the market, is a double benefit for the customer.

PCB schematic plays a special role whether it is used to analyze the circuit board principle and product working characteristics in reverse research or re-used as PCB design basis and basis in forward design.Then, according to the file diagram or object, how to do the PCB schematic diagram back, back process is what?What details should I pay attention to?

1. Backward steps:

1. Record PCB details

When you get a PCB, first record on paper the model, parameters and location of all components, especially the diode, the direction of the three-stage tube and the direction of the IC notch.Use your digital camera to take two pictures of the location of the components.A lot of PCB board more and more advanced above the diode triode some attention simply can not see.

2. Scanned images

Remove all components and remove the tin from the PAD hole.Clean the PCB with alcohol, and then put it into the scanner. The scanner needs to slightly increase the scanning pixel to get a clearer image.The top layer and bottom layer are lightly polished with water gauze paper until the copper film is shiny. Then, the scanner is put into PHOTOSHOP and the two layers are swept in color.Note that the PCB must be placed horizontally and vertically in the scanner, otherwise the scanned image will not be used.

3. Adjust and correct the image

Adjust the contrast and brightness of the canvas so that there is a strong contrast between the part with copper film and the part without copper film. Then change the secondary image to black and white to check whether the lines are clear. If not, repeat this step.If it is clear, save the image as black and white BMP files TOP BMP and BOT BMP. If there are any problems with the image, you can repair and correct it with PHOTOSHOP.

4. Verify the position coincidence between PAD and VIA

The two BMP files were converted into PROTEL files respectively, and the two layers were transferred into PROTEL. For example, the positions of PAD and VIA over the two layers were basically identical, indicating that the previous steps were well done. If there was any deviation, the third step was repeated.Therefore, PCB copy board is a very patient work, because a small problem will affect the quality and copy board after the matching degree.

5. Draw the layer

Convert BMP from TOP layer to TOP PCB, pay attention to the SILK layer, the yellow layer, then you just trace the line on TOP layer, and place the device according to the drawing in step 2.Delete the SILK layer after painting.Repeat until all the layers are drawn.

6. Combination of TOP PCB and BOT PCB

Add the TOP PCB and BOT PCB in PROTEL and 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, compare the errors, if yes, you are done.

Test 8.

Test whether the electronic technical performance of copy board is the same as the original board.If it's the same then it's really done.

Pay attention to details

1. Rationally divide functional areas

In the reverse design of a complete PCB circuit board schematic diagram, the rational division of functional areas can help engineers to reduce some unnecessary trouble, improve the efficiency of drawing.Generally speaking, the components with the same function on a PCB board will be arranged in a centralized way, so that the functional area can be divided according to the convenient and accurate basis when the schematic diagram is reversed.

However, the division of this functional area is not arbitrary.It requires the engineer to have some knowledge of electronic circuits.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 partition is the basis of schematic drawing.In addition, in this process, do not forget to skillfully use the component number on the circuit board, they can help you faster functional zoning.

2. Find the right reference

This reference can also be said to be the main component PCB network city at the beginning of schematic drawing. After determining the reference components, drawing according to the pins of these reference components can ensure the accuracy of schematic diagram to a greater extent.

Benchmark for engineers, a sure is not very complicated things, in general, can choose to play a leading role in the circuit components as a benchmark, they generally larger, pin more, convenient drawing, such as integrated circuit, transformer, transistor, etc., are suitable as a benchmark.

3. Correctly distinguish the lines and draw the wiring reasonably

For the distinction of ground wire, power line and signal wire, engineers also need to have relevant knowledge of power supply, circuit connection, PCB wiring, etc.The distinction of these circuits can be analyzed from the connection of components, the width of copper foil and the characteristics of electronic products themselves.

In wiring drawing, in order to avoid lines crossing and interweaving, grounding symbols can be widely used for ground wires, different lines with different colors can be used for various lines to ensure clear identification, special marks can be used for various components, and even unit circuits can be drawn separately and finally combined.

4. Master the basic framework and draw lessons from similar schematic diagrams

For some basic electronic circuit framework composition and schematic drawing method, engineers need to be skilled, not only to some simple, classical unit circuit basic form of direct drawing, but also to form the overall framework of electronic circuit.

On the other hand, do not neglect that the same type of electronic products have certain similarity in schematic diagram of PCB network city. Engineers can use the same circuit diagram for reference to carry out the reverse of new product schematic diagram based on the accumulation of experience.

5. Check and optimize

After the schematic drawing is completed, the reverse design of PCB schematic diagram can only be finished after the test and verification.The nominal value of components sensitive to PCB distribution parameters should be checked and optimized. According to THE PCB file diagram, the schematic diagram should be compared, analyzed and checked to ensure that the schematic diagram is completely consistent with the file diagram.