1, PCB painting outsourcing production requirements
Clear requirements for plate thickness, copper thickness, welding resistance, character color, etc. The above requirements are the basis for making a board, so R&D engineers must write clearly. As far as the customers I have contacted are concerned, Gree has done a relatively good job, and the technical requirements of each document are clearly written. Even the white characters in green solder resist ink, which we think is the most normal at ordinary times, are written in the technical requirements, while some customers can avoid writing anything, and send it to manufacturers for proofing. Especially, some manufacturers have not written out some special requirements.
2. Design of drilling
The most direct and biggest problem is the design of the minimum aperture. Generally, the minimum aperture in a board is the aperture of a via hole, which is directly reflected in the cost. Some boards’ vias can obviously be designed as 0.50MM holes, that is, only 0.30MM holes can be placed, so that the cost will rise directly and greatly. If the manufacturer’s cost is high, the quotation will be increased; In addition, there are too many through holes. Some DVDs and digital photo frames have really filled up the whole board, with more than 1,000 holes at every turn. Too many boards in this area have been made, and it is thought that the normal number should be 500-600 holes. Of course, some people have said that more holes are good for the signal conduction and heat dissipation of the board. I think it is necessary to strike a balance. While controlling these aspects, it will not lead to an increase in cost. Here, I can give you an example: our company has a customer who makes DVDs in Shenzhen, and the volume is very large. This was also the case at the beginning of the cooperation. Later, the cost was a big problem for both parties. After communicating with R&D, the hole diameter of the via was enlarged as much as possible, and some of the vias on the big copper skin were deleted. For example, the cooling holes in the middle of the main IC were replaced by four 3.00MM holes, so that the drilling cost was reduced. Other slots, such as the ultra-short slot of 1.00MM X 1.20MM, are really difficult for manufacturers to make. First, it is difficult to control the tolerance. Second, the slot from the drill is not straight, and some are bent. We have made some of these boards before, and as a result, the board with a few cents RMB will be deducted by USD 1/piece because the slot is unqualified. We also communicated with customers about this problem, and then we directly made it.
3. Outsourcing design of lines.
Outsourcing PCB painting design is the most common for manufacturers, such as line width and line spacing, and open circuit and short circuit. Apart from the special ones, for some conventional boards, I think the larger the line width and line spacing, the better. I have seen some documents, a line that could have gone straight, but there must be several bends in the middle. There are several large and small lines in the same row, with different spacing. For example, in some places, the spacing is only 0.10MM, while in others, it is 0.20. There are also some circuit pads or traces with a distance of only 0.127MM from the big copper skin, which increases the difficulty for manufacturers to handle films. It is best that the distance between the pad traces and the big copper skin is more than 0.25MM; Some routes are only a small safe distance from the periphery or V-CUT, so the manufacturer can move them well, while others can only be done if the R&D is well designed. There are even routes that are not connected in the same network, but some are clearly connected in the same network, but they are not connected. In the end, when the manufacturer communicates with R&D, it is found that it is a short circuit, and then the data needs to be revised again. This kind of situation is not rare, and experienced engineers may be able to see it. Inexperienced ones only follow the design documents. As a result, they either modify the documents to re-proof, or scrape off or fly the wires with a blade. For boards with impedance requirements, some R&D will not be written, and finally they do not meet the requirements. In addition, the vias of some boards are designed on SMD PAD, and the solder leaks during soldering.
4. Design of solder resistance.
The problems that are easy to occur in solder resistance are exposed copper on some copper skins or wires. For example, a solder resist window should be opened on the copper skin to facilitate heat dissipation, or copper should be exposed on some high-current lines. Generally, these additional solder resists are placed on the Soldermask layer, but some R&D’s are newly built, which are placed on the mechanical layer and the forbidden wiring layer. There are all kinds of them, which are hard to understand without saying or specifying. I think it is best to put it in the TOP Soldermask or BOTTOMSoldermasK layer, which is the easiest for people to understand. In addition, it is necessary to explain whether the green oil bridge in the middle of IC should be kept, and it is best to give an explanation as well.
5. Design of characters.
The most important aspect of characters is the requirement of word width and word height design. Some boards are not very good in this aspect either. As a manufacturer, I think it’s not beautiful. I think we must learn from those motherboard manufacturers. Row after row of component characters with the same size make people look pleasing to the eye. In fact, it is best to design the characters to be 0.80*0.15MM or more, and the silk-screen printing process of the manufacturer is also better to print; There are other big white oil blocks, such as those on the crystal oscillator, or those plugged in. Some manufacturers have to cover the pads with white oil, while others have to expose the pads. These must also be explained; I have also encountered some errors in screen printing position swap, such as the character swap of resistor and capacitor, but these errors are still rare; There are also signs that need to be added, such as UL LOGO, ROHS, PB logo, manufacturer’s logo and number.
6. Design of appearance.
Nowadays, the boards are rarely rectangular and irregular, but there are mainly several kinds of lines and outlines, which make people unable to choose. In addition, now, in order to improve the utilization rate of equipment (such as SMT), we have to make up V-CUT, but the pitches of the boards spelled out are different, some are spaced, some are not. It’s good to make a batch of proofing for the first factory, but it’s more troublesome to change suppliers later. If the second factory doesn’t follow the requirements. Therefore, in the absence of special circumstances, it is best not to spell spacing; In addition, some file designs may draw a small rectangular hole for the slot to be drilled and put it on the shape layer. This kind of situation is common in files designed by PROTEL software, and PADS is relatively good. It is easy for manufacturers to misunderstand that this hole should be punched out or made into NPTH attribute. For some files that require PTH attribute, it is easy to go wrong.
In addition, the blue glue process or carbon oil process board will not be mentioned here.
Judging from the above problems, some of them may be the habits of engineers, some may be the carelessness of engineers, and some may be the cultural system of the company. However, I always think that everyone should think more about the next process (in fact, the manufacturer is the next process of customers) and try not to guess with the next process, so as to avoid unnecessary mistakes, save time, cost and improve quality.