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PCB Tech

How to distinguish between good and bad PCB circuit boards and explain the PCB copying process in detail
2021-10-06
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Author:Downs

With the rapid development of the mobile phone, electronics, and communication industries, it also promotes the continuous growth and rapid growth of the PCB circuit board industry. People have more requirements for the number of layers, weight, precision, materials, colors, and reliability of components. Come higher.

There are two ways to distinguish whether a PCB circuit board is good or bad; the first method is to judge from the appearance, and the other is to judge from the quality specification requirements of the PCB board itself.

How to judge the quality of PCB circuit board

1. Identify the quality of the circuit board from the appearance

Under normal circumstances, the appearance of the PCB circuit board can be analyzed and judged through three aspects:

Standard rules for size and thickness: The thickness of the circuit board is different from that of the standard circuit board. Customers can measure and check the thickness and specifications of their own products.

Light and color: The external circuit board is covered with ink, and the circuit board can play the role of insulation. If the color of the board is not bright and less ink, the insulation board itself is not good.

pcb board

Weld appearance: circuit boards have many parts. If the welding is not good, the parts are easy to fall off the circuit board, which will seriously affect the welding quality of the circuit board. It is very important to have a good appearance, careful identification and a strong interface.

2. High-quality PCB circuit boards need to meet the following requirements

The phone is required to be easy to use after the components are installed, that is, the electrical connection must meet the requirements

The line width, line thickness, and line distance of the line meet the requirements to prevent the line from heating, breaking, and short-circuiting.

The copper skin is not easy to fall off under high temperature.

The copper surface is not easy to oxidize, which affects the installation speed, and it will be broken shortly after being oxidized.

There is no additional electromagnetic radiation.

The shape is not deformed, so as to avoid deformation of the housing and dislocation of the screw holes after installation. Now it is all mechanized installation, and the deviation of the hole position of the circuit board and the deformation of the circuit and the design should be within the allowable range.

High temperature, high humidity and resistance to special environments should also be considered.

The mechanical properties of the surface must meet the installation requirements.

The above is the way to judge the quality of PCB circuit boards. When buying PCB circuit boards, you must keep your eyes open.

One, the specific steps of PCB copy board

1. Get a piece of PCB, first record the model, parameters, and position of all vital parts on the paper, especially the direction of the diode, the tertiary tube, and the direction of the IC gap. It is best to use a digital camera to take two photos of the location of the vital parts. The current PCB circuit boards are getting more and more advanced. Some of the diode transistors above are not noticed at all.

2. Remove all the multi-layer boards and copy the boards, and remove the tin in the PAD hole. Clean the PCB with alcohol and put it in the scanner. When the scanner scans, you need to raise the scanned pixels slightly to get a clearer image. Then lightly polish the top and bottom layers with water gauze until the copper film is shiny, put them in the scanner, start PHOTOSHOP, and scan the two layers in 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 the contrast and brightness of the canvas to make the part with copper film and the part without copper film have a strong contrast, then turn the second image into black and white, and 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 picture, you can use PHOTOSHOP to repair and correct it.

4. Convert the two BMP format files to PROTEL format files, and transfer to two layers in 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 a deviation , Then repeat the third step. Therefore, PCB copying is a job that requires patience, because a small problem will affect the quality and the degree of matching after copying the board.

5. Convert the BMP of the TOP layer to TOP.PCB, pay attention to the conversion to the SILK layer, which is the yellow layer, and then you can trace the line on the TOP layer, and place the device according to the drawing in the second step. Delete the SILK layer after drawing. Keep repeating until all the layers are drawn.

6. Import TOP.PCB and BOT.PCB in PROTEL and combine them into one picture and it will be OK.

7. Use a laser printer to print TOP LAYER and BOTTOM LAYER on transparent film (1:1 ratio), put the film on that PCB, and compare whether there is any error. If it is correct, you are done.

Two, double-sided board copy method

1. Scan the upper and lower layers of the circuit board and save two BMP pictures.

2. Open the copy board software Quickpcb2005, click "File" "Open Base Map" to open a scanned picture. Use PAGEUP to zoom in on the screen, see the pad, press PP to place a pad, see the line and follow the PT to route... Just like a child drawing, draw it in this software, click "save" to generate a B2P file.

3. Click "File" and "Open Base Image" to open another layer of scanned color image;

4. Click "File" and "Open" again, and open the B2P file saved earlier. We see the newly copied board, stacked on top of this picture-the same PCB board, the holes are in the same position, but the wiring connections are different . So we press "Options"-"Layer Settings", turn off the top-level line and silk screen display here, leaving only multi-layer vias.

5. The vias on the top layer are in the same position as the vias on the bottom picture. Now we can trace the lines on the bottom layer as we did in childhood. Click "Save" again-the B2P file now has two layers of information on the top and bottom layers.

6. Click "File" and "Export as PCB File", and you can get a PCB file with two layers of data. You can change the board or output the schematic diagram or send it directly to the PCB plate factory for production.

Three, multi-layer board copy board method

In fact, the four-layer board copying is repeated copying two double-sided boards, and the sixth layer is repeated copying three double-sided boards... The reason why the multi-layer board is daunting is because we cannot see the internal wiring. How do we see the inner layers of a precision multilayer board?

There are many methods of layering, such as potion corrosion, tool stripping, etc., but it is easy to separate the layers and lose data. Experience tells us that sandpaper polishing is the most accurate.

In the PCB layout process, after the system layout is completed, the PCB diagram should be reviewed to see whether the system layout is reasonable and whether the optimal effect can be achieved. It can usually be investigated from the following aspects:

1. Whether the system layout guarantees the reasonable or optimal wiring, whether it can guarantee the reliable progress of the wiring, and whether it can guarantee the reliability of the circuit work. In the layout, it is necessary to have an overall understanding and planning of the direction of the signal, as well as the power supply and ground wire network.

2. Whether the size of the printed board is consistent with the size of the processing drawing, whether it can meet the requirements of the PCB manufacturing process, and whether there is a behavior mark. This point requires special attention. The circuit layout and wiring of many PCB boards are designed very beautifully and reasonably, but the precise positioning of the positioning connector is neglected, resulting in the design of the circuit cannot be docked with other circuits.

3. Whether the components conflict in two-dimensional and three-dimensional space. Pay attention to the actual size of the device, especially the height of the device. When welding components that are free of layout, the height should generally not exceed 3mm.

4. Whether the layout of the components is dense and orderly, neatly arranged, and whether they are all laid out. In the layout of components, not only the direction of the signal, the type of signal, and the places that need attention or protection must be considered, but also the overall density of the device layout must be considered to achieve uniform density.

5. Whether the components that need to be replaced frequently can be easily replaced, and whether the plug-in board can be easily inserted into the equipment. The convenience and reliability of replacement and connection of frequently replaced components should be ensured.