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How can I design a good PCB file?

writer: G May 16, 2019

1. Production requirements

Clear requirements for sheet, sheet thickness, copper thickness, process, solder mask/character color. The above is the basis

2. Design of drilling

The most direct and biggest problem is the design of the smallest aperture. Generally, the minimum aperture in the board is the aperture of the via. This is directly reflected in the cost. Some of the vias of the board can be designed as 0.50MM holes, but only 0.30MM, so the cost increases directly. If the cost is high, the price will increase.

In addition, there are too many vias. Normally, it should be in the range of 500-600 holes. Of course, some people will say that the holes are more conductive to the board and have better heat dissipation, but it will lead to cost increase. For example, the vias will be used. The aperture is increased as much as possible, and some of the via holes on the large copper skin are removed, and the heat dissipation holes in the middle of the main IC are replaced by four 3.00MM holes, so that the cost of drilling is reduced;

In addition, some slots, such as 1.00MM X 1.20MM ultra-short slots, for the manufacturer, it is really very difficult to do, first, it is difficult to control tolerance, second, the groove is not straight Some, bent, and later directly changed to a 1.20MM round hole.

3. Line design

For line width and line spacing, as well as open circuit short circuit, etc., is the most common manufacturer, aside from special, some more conventional boards, the larger the line width, of course, the better;

There are also some line pads, or the distance between the trace and the large copper is only 0.127MM, which increases the difficulty for the manufacturer to handle the film. The distance between the best pad and the large copper is 0.25MM or more;

Some traces have a small safety distance from the periphery or V-CUT, and then the data must be re-modified. For boards with impedance requirements, some R&Ds are not written. In addition, the vias of some boards are designed on SMD PAD, and the solder is drained when soldering.

4. Design of solder mask

In the case of solder masks, the problems that are more prone to occur are the need to expose copper in some copper or traces. For example, a solder mask should be added to the copper to facilitate heat dissipation, or copper should be exposed on some high current traces. Generally, these additional solder resists are placed on the Soldermask layer, but some R&Ds are newly built. , placed on the mechanical layer, placed on the circuit layer is prohibited. Ideally, it is placed on the TOP Soldermask or BOTTOM SoldermasK layer.

In addition, it is necessary to explain whether the green oil bridge in the middle of the IC should be retained.

5. Character design

The most important aspect of the character is the requirement of the word width and height design. The row of component characters and the same size make people look pleasing to the eye.

In fact, the character is best designed to be 0.80*0.15MM or more, and the silk screen printing process is better.

In addition, some large white oil blocks, such as those on the crystal oscillator, or some of the plugs, some manufacturers use white oil to cover the pads, and some expose the pads. These must also be explained;

I also encountered some screen printing position misalignment errors, such as the resistance of the resistors and capacitors changed;

There are also signs that need to be added, such as UL mark, ROHS typeface, PB mark, manufacturer's LOGO and number.

6. Shape design

Today's boards are rarely the kind of rectangles, they are all irregular. In addition, nowadays, in order to improve the utilization rate of equipment (such as SMT), the V-CUT must be imprinted, but the board spacing is different. There is spacing, some have no spacing, it is okay to make the batch for the first factory. If you want to change the supplier later, it will be more troublesome. If the second factory is not in accordance with the first factory, the steel mesh will not be able to fit. . Therefore, in the absence of special circumstances, it is best not to have a spacing;

In addition, some file designs may draw a small rectangular hole in the slot to be drilled. It is easy for the manufacturer to misunderstand that the hole is to be punched out or made into an NPTH attribute. For some, the PTH attribute is required. Say, it is easy to go wrong.

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