PCB Tech - Basic knowledge of PCB copy board

1. Copy board type

The question of which types of boards can be copied and which cannot be copied is actually very simple. As long as the copying software can directly open and save the PROTEL PCB file, all the placed element attributes fully support the PROTEL format, including the placement function, you can copy it out Any type of board.

2. Selection of copy board software

The quality of the board copy software mainly depends on whether the function is complete. PCB copy board, it is best to do all the work in the copy board software, so that the efficiency is high, including the placement of components supporting PROTEL99SE is the best, PCB copying The 99SE component library is very rich at present, which can be downloaded to the PCB copy board on the Internet. This is also a very critical matter. The era of manual PCB copying of components has passed, because many components like BGP have hundreds of elements in the package, and it is too expensive to build components manually.

For the stability and reliability of the circuit, the PCB copy board generally needs a large piece of copper to be connected to the power or ground when designing the circuit, which can reduce the noise and interference of the circuit. Therefore, it involves the problem of copper paving on the network. For complex circuit boards, many of the copper layers are connected and many are isolated. If this problem is not solved well, copper paving cannot be achieved, so here must be Define the network to lay copper ("the same network is connected, but different networks are isolated"). Simply filling everything with copper will cause a short circuit. This is also a key issue in measuring copy board software.

3. Grinding board

For multi-layer boards, the middle layer cannot be scanned directly. If you want to copy a multi-layer board from a PCB copy board, you must grind out multiple layers, so copying a multi-layer board must scrap a board.

The best method currently used is to use a good grinder and manual sanding with gauze paper. The latter method is the lowest cost method. Sandpaper is ordinary sandpaper that can be purchased everywhere in the market, but it must be coarse sandpaper., It is difficult to grind the fine sandpaper for PCB copy board.

As for the method is very simple, press the board to a good level and use sandpaper. If there is a large piece of copper on the PCB copy board, you can directly pull it off with pliers, or you can use a flat set to polish off the difficult ones, and then use it. Sandpaper again.

Grinding board is not a very technical work. Relatively speaking, experience is more important, so it is important to practice. Grinding a multilayer board will naturally master the basic essentials.

4. Copy board accuracy

The accuracy of copy board depends on two links, one is the accuracy of the software and the other is the accuracy of the original image.

For software accuracy, the 32-bit floating point representation can be said to have no accuracy limitations, so the most important thing depends on the image accuracy of the original scan. For example, if you use 1 million pixels to take a photo, it can be washed. 5-inch photo, but if you want to wash it into a 20-inch photo, it’s not clear at all. The reason is the same. Therefore, for a circuit board with high precision requirements, if you want to copy a very high-precision PCB diagram, When scanning, choose a higher DPI.

The meaning of DPI is how many dots per inch. That is to say, the distance between every two points on the scanned image is 1000/DPI, the unit is mil.

If the DPI is 400, then the distance between two points on the image is 1000/400 = 2.5 mil, which means that the accuracy at this time is 2.5 mil.

This is the most scientific basis, so some people say that the accuracy can be less than 1mil, and that is a prerequisite. In fact, the accuracy of copy board mainly depends on the original scanning accuracy.

To sum up, when scanning the board, setting the DPI should be based on the accuracy required by the actual board. If the accuracy of the cell phone board line spacing is required to be below 1mil, then the scanning DPI should be set above 1000DPI. . Scanners currently on the market can meet this condition. As the complexity of printed circuit boards continues to increase, the identification of manufacturing defects has become challenging. Many times, PCB may have defects such as open circuit and short circuit, wrong direction, inconsistent soldering, misalignment of components, wrong component placement, defective non-electrical components, missing electrical components, etc. When the DPI is higher, the picture is clearer and the accuracy is higher, but the disadvantage is that the picture is too large and requires higher hardware, so it should be set according to the specific situation. For boards with general accuracy, 400DPI is generally good, and mobile phone boards can be set above 1000DPI.