How to be considered a good PCB design? Here we will talk about the working methods and work habits in the design will make your design more reasonable, easier to produce and better performance.
1 Production requirements
For the plate plate thickness copper thickness process solder resist / character color and other requirements clear. The above requirements are the basis for the production of a board, so R & D engineers must write clear, this in my contact with the customer to see, GREE is doing relatively well, each file of technical requirements are written very clear, even if it is usually we think the most normal with green solder resist ink white characters are written in the technical requirements are reflected, while some customers are exempt, nothing is written, sent to manufacturers to sample Production, especially some manufacturers have some special requirements are not written out, resulting in manufacturers after receiving the mail, the first thing is to consult the requirements in this regard, or some manufacturers finally do not meet the requirements.
2 drilling design
The most direct and biggest problem is the design of the minimum aperture, the minimum aperture of the general board is the aperture of the hole, which is directly reflected in the cost, some of the board’s hole can be designed for 0.50MM hole, that is, only put 0.30MM, so that the cost directly rose sharply, the manufacturers of high costs, will increase the offer; another is too many holes, some DVD and digital photo frame Some DVDs and digital photo frames are really full of holes on the whole board, moving more than 1000 holes, have done too much in this area of the board, that the normal should be in 500-600 holes, of course, some people will say that more holes on the board signal conduction, as well as the benefits of heat dissipation, I think it is necessary to take a balance, in the control of these aspects at the same time will not lead to rising costs, I can say here an example: our company After communication with R & D, the aperture of the hole will be increased as much as possible, delete the large copper skin on the part of the hole, like the main IC middle of the heat sink hole with four 3.00MM holes instead, so that the cost of drilling is reduced, a square can The other is some slot holes, such as 1.00MM X 1.20MM ultra-short slot holes, for manufacturers, it is really very difficult to do, the first is difficult to control the tolerance, the second drilling also to the slot is not straight, some curved, we have done part of such a board, the results of a few cents of the board, because the slot holes do not pass, deducted 1 USD / piece, we also do part of such a board, the results of a few cents of the board, due to the slot holes. Deduction of 1 U.S. dollars / block, we also communicated with customers in this regard, and later directly changed to use 1.20MM round hole.
3 Wire design
For the line width line spacing, and open short circuit, etc., is the most common manufacturers, leaving aside the special, some of the more conventional board, I think the line width line spacing, of course, the greater the better, I have seen some documents, a line can go straight, the middle of the non-existent several bends, the same row of several wide size of the same line, the spacing is not the same, such as some places only 0.10MM spacing, some places have 0.20MM, I think R & D in wiring, we should pay attention to these details; there are some line pads or alignment and large copper skin distance of only 0.127MM, increasing the difficulty of manufacturers to deal with the film, the best pad alignment and large copper skin distance of 0.25MM or more; some alignment is very small from the periphery or V-CUT at the safety distance, manufacturers can move okay, some must be R & D must be designed to do, even if there is not the same network of alignments connected together, and some are clearly the same network, but not connected, to the end of the manufacturers and R & D communication, it was found to be a short circuit open, and then to re-modify the information, this situation is not a few, experienced engineers may be able to see, inexperienced is only to follow the design of the file to do, the result is either modify Files to re-sample or scrape with a blade or fly line, for the line has impedance requirements of the board, some R & D also do not write, and finally is not in line with the requirements. In addition, some of the board’s over-hole design in the SMD PAD, soldering is leaking tin down.
4 solder resist design
In the solder resist aspect of the more likely to appear in some copper skin or alignment to expose copper these aspects. For example, in the copper skin to open the solder resist window to facilitate heat dissipation, or in some high-current alignment to reveal copper, generally these additional solder resist is placed on the Soldermask layer, but some R&D is another new layer, placed on the mechanical layer, placed on the prohibited wiring layer, a variety of everything, which does not say, but also does not specify, it is difficult for people to understand. I think the most ideal or placed on the TOP Soldermask or BOTTOMSoldermasK layer is the best, so that people are the easiest to understand. In addition it should be stated whether the green oil bridge in the middle of the IC should be kept, and it is better to give a description as well.
5 Character design
The most important aspect of the character is the word width word height design requirements, some board this aspect is not very good, the same component even appear several character size, I as a manufacturer are considered unattractive, these I think we must learn from those motherboard manufacturers, a row of component characters, the same size, so that people look are pleasing to the eye. In fact, the character is best designed for 0.80 * 0.15MM or more, manufacturers do screen printing process is also better printed; in addition is some large white oil blocks, such as crystal oscillators, or some row of plugs, some manufacturers to cover the pads with white oil, some to reveal the pads, these are also necessary to explain; also encountered some screen printing position on the wrong, such as the resistor and capacitor characters swapped, but These errors are still rare; there is also the need to add the logo, such as UL logo, ROHS characters, PB logo, the manufacturer’s LOGO and number.
6 Design of the shape
Now the board is rarely the kind of rectangular and so on, are irregular, but mainly there are several line drawing frame, so that people can not choose, in addition, now in order to improve the utilization of equipment (such as SMT), are to spell V-CUT, but spell out the board spacing is different, some have spacing, some do not have spacing, to the first factory to sample to do batch okay, if you want to change the supplier to the back is more trouble If the second factory is not in accordance with the first factory to spell, the stencil will not be set. So in no particular case, it is best not to spell with spacing; in addition, some documents may be designed to draw a small rectangular hole to be drilled out of the slot hole in the shape layer, this situation is more common in the PROTEL software design files, as opposed to PADS is better, that put in the shape layer, in the manufacturers are easy to misunderstand that the hole to be punched out or made into NPTH properties, for Some are to PTH properties, it is easy to go wrong.
PCB design is a meticulous work, the need for care and patience. Beginning to do the design of the newcomer often make mistakes is some of the details of the error. Device pins are wrong, the wrong device package, the pin order is drawn backwards and so on, some can be solved by flying the line, some may let a board directly into the scrap. When drawing the package more than once, before the board to print out the package and the actual device than a look, more than once to check is not OCD, just so that these easy to make low-level mistakes to avoid. Otherwise, the design of a good-looking board, covered with flying lines, it is far from excellent.