Electronic Design - Master the backward step, PCB schematic can also learn very easily

That is, on the premise of having physical electronic products and printed circuit boards, reverse analysis of circuit boards is carried out by means of reverse research and development technology, and the ORIGINAL product PCB files, BOM files, schematic diagram files and other technical documents as well as PCB silkscreen production files are restored 1:1.

Then use these technical documents and production documents for PCB board making, component welding, flying needl

e test, circuit board debugging, complete the original circuit board sample copy.

For PCB copying board, many people do not understand, what is PCB copying board, some people even think PCB copying board is copycat.

In everyone's understanding, shanzhai means imitation, but PCB copying is not imitation. The purpose of PCB copying is to learn foreign electronic circuit design technology, and then absorb the design scheme, and then use it to develop and design more products.

With the continuous development and deepening of the board copying industry, today's PCB board copying 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 research and development of new products.

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 technology trends, timely adjustment to improve product design, research and development with market competitive new products.

In the process of PCB board copying, through the extraction and partial modification of technical data files, it can realize the rapid update, upgrading and secondary development of various types of electronic products. According to the file diagram and schematic diagram extracted from PCB copying, designers can also optimize the design and change the PCB according to the customer's wishes.

On this basis, it can also add new functions for the product or redesign the functional features, so that the product with new functions will appear at a fast speed and a new posture, not only has its own intellectual property rights, but also wins the first opportunity in the market, bringing double benefits to customers.

Whether it is used to analyze circuit board principle and product working characteristics in reverse research, or used as the basis of PCB design in forward design, PCB schematic has a special role.

So, according to the document or object, how to carry out the PCB schematic diagram backward, what is the backward process? What are the details to pay attention to?

Backstepping steps

1. Record PCB related details

Get a PCB, first on the paper to record all the components of the model, parameters, and location, especially the diode, the direction of the three-stage tube, IC notch direction. Take two pictures of the location of the component with your digital camera. A lot of PCB circuit boards do more and more above the diode triode some do not pay attention to simply see.

2. Scanned images

Remove all components and remove tin from PAD holes. Clean the PCB with alcohol and place it into a scanner that scans at slightly higher pixels to get a sharper image.

Then, polish the top and bottom layers lightly with water yarn paper until the copper film is shiny. Put them into the scanner, start PHOTOSHOP, and brush the two layers separately in color.

Note that PCB must be placed horizontally and vertically in the scanner, otherwise the scanned image can not be used.

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 contrast strongly, then turn the subgraph to black and white, check whether the lines are clear, if not, repeat this step. If clear, the picture will be saved as black and white BMP format files TOP BMP and BOT BMP, if the figure is found to have problems can also be repaired and corrected with PHOTOSHOP.

4. Verify the position coincidence of PAD and VIA

Convert the two BMP files into PROTEL files respectively, and transfer two layers into PROTEL. For example, the positions of PAD and VIA after two layers basically coincide, indicating that the previous steps have been done well. If there is any deviation, repeat the third step. Therefore, PCB board copying is a very patient work, because a little problem will affect the quality and the matching degree after board copying.

5. Draw layers

Convert TOP layer BMP to TOP PCB, make sure to convert SILK layer, the yellow layer, then you 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 you have drawn all the layers.

6. Combination of TOP PCB and BOT PCB

Add TOP PCB and BOT PCB in PROTEL and combine them into one figure.

7. laser printing TOP LAYER, BOTTOM LAYER

Use the laser printer to print the TOP LAYER and the BOTTOM LAYER on transparent film (1:1 ratio), put the film on that PCB and compare if it is wrong, if it is right, you are done.

8. Test

Test the electronic performance of copy board is not the same as the original board. If it's the same then it's really done.

Attention to detail

1. Reasonably divide functional areas

When reverse designing the schematic diagram of an intact PCB, reasonable division of functional areas can help engineers reduce some unnecessary trouble and improve the efficiency of drawing.

Generally speaking, components with the same function on a PCB board will be arranged centrally, so that the functional division of areas can provide a convenient and accurate basis for reverting the schematic diagram.

However, the division of this functional area is not arbitrary. It requires engineers to have a certain understanding of electronic circuit related knowledge.

First of all, find out the components of a functional unit, and then according to the wiring connection can be traced to find out the other components of the same functional unit, the formation of a functional partition.

The formation of functional partition is the basis of schematic drawing. In addition, don't forget to use the component number on the circuit board to help you partition functions faster.

2. Find the right reference parts

This reference piece can also be said to be the main component PCB network city at the beginning of schematic drawing. After determining the reference pieces, drawing according to the pins of these reference pieces can ensure the accuracy of schematic drawing 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 lines and reasonably draw wiring

For the distinction of ground wire, power line and signal line, engineers also need to have relevant knowledge of power supply, circuit connection, PCB wiring and so on. 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 the wiring drawing, in order to avoid line crossing and interspersing, the ground can use a large number of grounding symbols, all kinds of lines can use different colors of different lines to ensure clear discernable, for all kinds of components can also use special signs, and can even separate the unit circuit drawing, and then combined.

4. Master the basic framework and refer to similar schematic diagrams

For some basic electronic circuit frame composition and principle drawing method, engineers need to master, not only to be able to draw some simple, classic basic composition of the unit circuit directly, but also to form the overall frame of the electronic circuit.

On the other hand, do not ignore that the same type of electronic products have certain similarities in the schematic diagram of PCB network city, engineers can according to the accumulation of experience, fully draw on similar circuit diagram to carry out the reverse of the new product schematic diagram.

5. Check and optimize

After the schematic drawing is completed, the reverse design of PCB schematic diagram can be concluded only after testing and checking. The nominal values of components 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 is completely consistent with the file diagram