Electronic Design - What to pay attention to when designing high-performance PCB

1. Production requirements

Clear requirements for plate, plate thickness, copper thickness, process, solder mask/character color, etc. The above requirements are the basis for making a board, so the RD engineer must write clearly, the technical requirements of each document are written very clearly, even if we think the most normal use of green solder mask, white characters are written in the technical requirements., And some customers are exempt if they can avoid it. If nothing is written, they will be sent to the PCB manufacturer for production. Especially some PCB manufacturers have not written down some special requirements, which causes the PCB manufacturer to do the first thing after receiving the email. It is to consult the requirements in this regard, or some PCB manufacturers finally made non-compliance with the requirements.

2. the line

The line width and line spacing, as well as open circuit and short circuit, are the most common ones for PCB manufacturers. Apart from special ones, for some more conventional boards, I think the line width and line spacing are of course the larger the better. I have seen some documents. You can walk straight and straight, but there must be a few bends in the middle. There are several lines of the same width and size in the same row, with different spacing. For example, the spacing is only 0.10MM in some places, and 0.20MM in some places. I think RD When wiring, pay attention to these details; there are also some circuit pads or traces and the distance between the large copper skin is only 0.127MM, which increases the difficulty of the PCB manufacturer to deal with the film. The distance is more than 0.25MM; some traces have a small safety distance from the periphery or V-CUT. It is okay for PCB manufacturers to be able to move them. For some traces, the RD must be designed well before they can be done. There are even traces that are not the same network. They are connected together, but some are obviously on the same network, but they are not connected. At the end of the communication with the RD, the manufacturer finds that it is a short circuit and an open circuit, and then the data needs to be revised. This situation is not rare. An experienced engineer may be able to It can be seen that those with inexperience only follow the design documents, and the result is either to modify the document and re-proof, or use a blade to scrape or fly the line. For the boards with impedance requirements, some RDs are not written, and finally they do not meet the requirements. . In addition, the through holes of some boards are designed on the SMD PAD, and the tin leaks when soldering.

3. Drilling

The most direct and biggest problem is the design of the smallest aperture. Generally, the smallest aperture in the board is the aperture of the via. This is directly reflected in the cost. The vias of some boards can obviously be designed as 0.50MM holes, namely Put only 0.30MM, so the cost will directly rise sharply, PCB manufacturers will increase the price if the cost is high; in addition, there are too many vias, and they think that the normal should be 500-600 holes. Of course, some people will say that there are many signals for the board. There are advantages in conduction and heat dissipation. I think there must be a balance to control these aspects while not causing cost increases; the other is some slots, such as ultra-short slots of 1.00MM X 1.20MM Hole, for PCB manufacturers, is really very difficult to make. First, it is difficult to control the tolerance, and the second hole is not straight.

4. solder mask

The problems that are more likely to occur in solder mask are some copper skins or traces where copper should be exposed. For example, a solder mask should be opened on the copper skin to facilitate heat dissipation, or copper should be exposed on some high-current traces. Generally, these additional solder masks are placed on the Soldermask layer, but for some RDs, a new layer is created., On the mechanical layer, on the forbidden wiring layer, there are all kinds of things, not to mention, without special instructions, it is difficult for people to understand. I think the most ideal is to put the TOP Soldermask or BOTTOMSoldermasK layer is the best, it 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, and it is best to give an explanation.

V. Characters

The most important aspect of characters is the design requirements of character width and character height. Some boards are not very good in this aspect. There are even several character sizes in the same component, which is not beautiful. The component characters that should be arranged in a row, the same size, make people look pleasing to the eye. In fact, it’s best to design the characters above 0.80*0.15MM, and PCB manufacturers can do the silk-screen printing process better; in addition, there are some large white oil blocks, such as the crystal oscillator, or some plug-in, some PCB manufacturers need to use white Oil covers the pads, and some have to expose the pads. These must also be explained; I have also encountered some wrong silk screen positions, such as swapping the characters of resistors and capacitors, but these errors are still rare; It is the logo that needs to be added, such as UL logo, ROHS word, PB logo, PCB manufacturer's LOGO and serial number.

5. appearance

Nowadays, the boards are rarely rectangular, and they are all irregular, but mainly there are several kinds of line drawing outlines, which make people unable to choose. In addition, in order to improve the utilization rate of the equipment (such as SMT), V-CUT must be made up, but the board pitches are different. Some have pitch and some have no pitch. It is okay for the first PCB factory to make samples in batches. It will be more troublesome to change the supplier later, if the second one The factory does not follow the first factory to fight, the steel mesh will not fit. Therefore, under no special circumstances, it is best not to have spacing; in addition, some file designs may draw a small rectangular hole on the outline layer for the slot to be drilled. This situation is more common in files designed by PROTEL software. Relatively speaking, PADS is better. It is easy to be misunderstood by PCB manufacturers to punch out this hole or make it into NPTH attribute when it is placed on the shape layer. For some PTH attributes, it is easy to cause problems.