For simple double-sided panels and single-sided panels, everyone knows his method of copying the boards. You only need to remove the components, make a library of the corresponding components on them, put them in the corresponding positions, and connect the lines. But note that the back must be turned horizontally. This is done.
What about multi-layer PCBs? Although everyone has some understanding, their understanding of the structure and wiring rules of high-end PCB boards containing laser holes, blind holes, and buried holes is even better than others. Whether it is computer motherboards, high-end graphics card boards, gigabit network equipment substrates with dense components and microstrip lines and equal-length lines, or PHS motherboards, mobile phone motherboards, and wireless network cards that have demanding high-frequency processing requirements and strict electromagnetic compatibility control and other wireless communication equipment, as well as industrial control motherboards with up to 28 layers and densely packed blind and buried vias, we can successfully clone them in one go based on a complete set of samples (or prototypes) provided by the customer.
The following are some experiences summarized by engineers:
Step 1: Disassemble the components and make the BOM list: Aim the air gun at the component to be disassembled and heat it, clamp it with tweezers and let the wind blow it away. Remove the resistor first, then the capacitor, and finally the IC. And record whether there are components that have been dropped or installed upside down. Before disassembly, you should prepare a table with the serial number, package, model, value and other recording items. Paste double-sided tape on the column of the component record and record. After assigning the part number, paste the removed components one by one to the position corresponding to the part number. After disassembling all the devices, use a bridge to measure their values (the values of some devices will change under the action of high temperature, so they should be installed on all devices. After the device has cooled down, measure again (the measured value will be more accurate at this time). After the measurement is completed, enter the data into the computer for archiving.
The second step is to carry out PCB copying: After scanning the surface image, define it as the top layer and the bottom layer respectively, convert them into a base map that can be recognized by various copying software, and first package the components according to the base map (including silk screen printing). , pad aperture, positioning holes, etc.), after all components are completed, place them in the corresponding positions, adjust the characters so that their font, size and position are consistent with the original board, and you can proceed to the next step.
Use sandpaper to remove the silk screen, ink and characters on the surface of the PCB to expose the bright copper (there is an important tip for grinding and grinding the pad - the grinding direction must be perpendicular to the scanning direction of the scanner). Of course, there is another method that can make the ink fall off by heating it with an alkaline liquid, but it takes longer. Usually the former method is more environmentally friendly and harmless to the human body. Having a clear and complete PCB base map is an important prerequisite for copying the PCB board well. For a multi-layer PCB, the order of copying is from outside to inside. Take an 8-layer board as an example:
First remove the first and eighth layers of ink and copy the first and eighth layers, then grind off the copper of the first and eighth layers, then copy the second and seventh layers, then the third and sixth layers, and finally copy the fourth and fifth layers. . During the operation, please note that there is an error between the scanned image and the actual board. It should be processed appropriately to make its size and direction consistent with the actual board. After ensuring that the size of the base map is correct, start adjusting the positions of the PCB components one by one so that they completely coincide with the base map for the next step of placing vias, tracing wires, and laying copper. During this process, attention should be paid to details such as the width of the board, the size of the aperture, and the parameters of exposed copper. Be careful. This is the most important point, and it is also the step that determines the correctness of the PCB.
Step 3: Inspection: A complete inspection method will directly affect the quality of a PCB diagram. Using image processing software, combined with PCB drawing software and the physical connection relationship of the circuit, a 100% accurate judgment can be made. Impedance has a great influence on high-frequency boards. If there is only a physical PCB, you can use an impedance tester to test it or slice the PCB into slices. Use a metallographic microscope to measure its copper thickness and layer spacing. In addition, you must also analyze the dielectric of the base material. Constant (usually using FR4, PTFE, RCC as the medium), so as to completely ensure that the PCB indicators are consistent with the original board.
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