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What aspects of good PCB design should be considered

Posted:10:21 AM July 24, 2018 writer: G

1. Production requirements

Clear requirements for sheet, plate thickness, copper thickness, process, solder mask/character color. The above requirements are the basis for making a board, so R&D engineers must write clearly. This is a relatively good job for the customers I contact. The technical requirements of each document are clearly written, even if it is usually us. It is believed that the most normal white characters for green solder mask inks are written in the technical requirements, while some customers can avoid them and write them to the manufacturers for proofing. In particular, some manufacturers have some special requirements. Did not write, resulting in the manufacturer after receiving the mail, the first thing is to consult this request, or some manufacturers did not meet the requirements.

2. Design of drilling

The most direct and biggest problem is the design of the minimum aperture. 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. Only put 0.30MM, so the cost will increase directly, the cost of the manufacturer is high, it will increase the quotation; the other is that there are too many vias, some of the vias on the DVD and the digital photo frame are really full, and they are still moving. 1000 porous, has done too many boards in this respect, think that normal should be in the 500-600 hole, of course, some people will say that the hole is more on the signal conduction of the board, and the heat is good, I think it is necessary to take a balance In controlling these aspects, it will not lead to cost increase. I can say here an example: Our company has a customer who is a DVD in Shenzhen, which is very large. This is also the case when we first cooperated. Later, the cost is really a big problem for both parties. After communicating with R&D, the aperture of the via hole is increased as much as possible, and some of the via holes on the large copper sheet are removed, like the heat dissipation in the middle of the main IC. Replace with 4 3.00MM holes, so that the cost of drilling is reduced. One square can reduce the drilling cost of tens of dollars. For both parties, a win-win situation is achieved; in addition, some slots, such as Said 1.00MM X 1.20MM ultra-short slot, for the manufacturer, it is really very difficult to do, the first is difficult to control the tolerance, the second drill also comes to the slot is not straight, some curved, before we also I have done some of these boards. As a result, the board with a few cents of RMB, because the slot is unqualified, deducted 1 US dollar / block, we also passed the problem with the customer ditch, and then directly changed to 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 the special, some more conventional boards, I think the line width is of course larger, the better, I have seen some documents, one could have Go straight, there are a few bends in the middle, and several rows of the same width and the same line, the spacing is not the same, for example, the spacing is only 0.10MM in some places, 0.20MM in some places, I think R&D is When wiring, we must pay attention to these details; there are some circuit pads or traces and the distance between the copper and copper is only 0.127MM, which increases the difficulty for manufacturers to deal with the film. The best distance between the pad and the large copper is More than 0.25MM; some traces are safe from the periphery or V-CUT, the manufacturers can move back, and some must be designed for R&D, even if they are not connected to the same network. And some of them are clearly the same network, but they are not connected. When the last manufacturer communicates with R&D, they find that they are short-circuited and then re-edit the data. This is not a small number of experienced projects. It may be seen that the inexperienced ones only follow the design files. The result is either to modify the file to re-sample or use a blade to scrape or fly the line. For boards with impedance requirements, some R&D does not write, and finally does not. Meet the requirements. In addition, the vias of some boards are designed on SMD PAD, and the solder is drained when soldering.

4. Design of solder mask

The problem that is more prone to soldering is that some copper or traces should be exposed to copper. 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. On the mechanical layer, placed on the banned wiring layer, there are all kinds of things, there is nothing, this does not say, not specifically stated, it is difficult to make people understand. I think the best thing is to put it in the TOP Soldermask or BOTTOMSoldermasK layer, which is the easiest to understand. 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 character is the design of the word width and height. Some boards are not very good in this aspect. The same kind of components even appear in several characters. I think it is not good as a manufacturer. I think we must learn from those motherboard manufacturers. The row of component characters, the same size, makes people look pleasing to the eye. In fact, the character is best designed to be 0.80*0.15MM or more. The manufacturer does the silkscreen printing process. The other is the large white oil block, such as the crystal oscillator, or some of the plugs. Some manufacturers use white oil to cover. Live pads, some have to expose the pads, these must also be explained; also encountered some silk screen position misalignment errors, such as the resistance and capacitance of the character swap, but these errors are still very few; Plus signs, 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, but there are mainly several kinds of line drawing frames, which makes people unable to choose. In addition, now, in order to improve the utilization of equipment (such as SMT), We must imposition V-CUT, but the board spacing is different, some have spacing, some have no spacing, it is better to give the first factory proofing batch, if it is to be changed later, it is more troublesome if the second factory Not according to the first factory to fight, the steel mesh can not be set. Therefore, in the absence of special circumstances, it is best not to have a spacing; in addition, some file design may put a small rectangular hole in the slot to be drilled in the shape layer, which is more common in PROTEL software design files. Relatively speaking, PADS is better. It is easy to misunderstand that the hole is to be punched out or made into NPTH attribute. It is easy for some PTH attributes to be problematic.

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