PCB copy board steps
The first step: preparation
Get a good circuit board to see if there are components with high position. If you have the component number, component package, temperature value, etc., make detailed records. Scan as a backup before disassembling the component. After removing the higher components, the SMD and some smaller components are left. At this time, the second scan is performed to record the image. It is recommended that the resolution be 600 dpi. Always remove any dirt from the PCB surface before scanning to ensure that the IC model and characters on the PCB are clearly visible on the image after scanning.
Step 2: Disassemble the components and make a BOM
Use a small air gun to heat the components to be removed, and clamp the electronic components with tweezers to prevent the wind from blowing them away. First remove the resistor, then remove the capacitor, and finally remove the IC. And record whether there are any components that have been dropped and previously installed.
Before disassembly, prepare a table with record number, package, model, value, etc., and attach double-sided tape to the column of the component record. After the lower number, the removed components are pasted one by one to the position corresponding to the bit number. After disassembling all the devices, the values are measured by the bridge (some devices will change their values under the action of high temperature, so it should be at all After the device is cooled down, the measurement is performed, and the measured value is more accurate. After the measurement is completed, the data is input into the computer for archiving.
The third step: surface residual tin removal
By using flux, the surface of the PCB from which the component is removed is removed by a tin-absorbing wire. The temperature of the soldering iron is appropriately adjusted according to the number of layers of the PCB. Since the heat dissipation of the multilayer board is not easy, the tin is melted, so Increase the temperature of the soldering iron, but not too high to avoid boiling the ink. The plate from which the tin is removed can be washed with washing water or Tianna water and dried.
Step 4: Real-time operation in the copy board software
Scan the surface image and set it as the top and bottom layers respectively, convert them into a base map that can be recognized by various copy board software, and first package the components according to the base map (including small screen printing, pad aperture, positioning holes, etc.) ), after all the components are ready, put them in the corresponding position, adjust the characters, make the font, font size and position consistent with the original board, you can proceed to the next step.
Use sandpaper to polish the silk screen, ink and characters on the surface of the PCB to expose the bright copper (the sanding pad has an important flaw - the direction of the grinding must be perpendicular to the direction scanned by the scanner). Of course, there is another way to warm the ink with an alkaline liquid, but it takes a long time. The former method is generally environmentally friendly and harmless to the human body. A clear and complete PCB basemap is an important prerequisite for copying a PCB.
The order of copying a multi-layer PCB is from the outside to the inside. Take an 8-layer board as an example:
First remove the one and eight layers of ink after copying one or eight layers, then grinding off one and eight layers of copper, then copying the second and seventh layers, then three and six layers, and finally copying the fourth and fifth layers. . During the operation, it is necessary to pay attention to the error between the scanned image and the real board. It should be properly processed to make the size and direction consistent with the solid board. After making sure that the basemap is the correct size, start to adjust the position of the PCB components one by one to make it completely coincide with the basemap for the next step of placing the vias, drawing wires and copper. In this process, attention should be paid to details such as the width of the board, the aperture size, and the parameters of the exposed copper.
Step 5: Check
A perfect inspection method will directly affect the quality of a PCB diagram, using image processing software, combined with PCB drawing software and circuit physical connection relationship can make 100% accurate judgment. The impedance has a great influence on the high-frequency board. In the case of only the physical PCB, the impedance tester can be used to test or slice the PCB, the copper thickness and the layer spacing are measured by a metallographic microscope, and the dielectric of the substrate is also analyzed. The constant (usually FR4, Teflon, RCC as the medium), so that the PCB specifications are fully consistent with the original board.