PCB News - MRB meeting of PCB manufacturing plant and quality judgment of plastic parts

MRB meeting of PCB manufacturing plant and quality judgment of plastic parts

I remember that when I first came into contact with PCBA processing plants, I often needed to participate in MRB meetings, and I was also escorted from time to time to judge whether some of the rejected parts could be used for special procurement, otherwise the production line would be in danger of material interruption. A few people can afford the loss of the line stop. At that time, the most annoying thing was plastic parts, but more than 70% of the defective returned parts in the finished product assembly factory were almost all related to plastic parts~

Note: MRB is usually composed of shipping, production control, quality control, process and other units in the factory. The purpose is to discuss and solve various incurable problems in production.

Because the dimensional variability of plastic parts is often very large, it is often the phenomenon of structural deformation, insufficient or too large shrinkage rate when injection molding is not paid attention to, resulting in out-of-standard dimensions. Sometimes these problems obviously do not need to be concerned. However, the designer will mark the tolerances very small in the size marking, and some will be marked as key dimensions, so they often have to pick up these out-of-specification parts to actually assemble them to confirm whether they can be used and whether there are functional problems. Sometimes it is necessary to communicate the tolerances of the dimensions with the design engineer. If there is enough time and ability, these issues should be raised at the stage of DFM review before mass production. However, because the pre-marketing manufacturing industry is getting shorter and shorter, many people will excuse the tight time and ignore it intentionally or unintentionally. These pre-jobs have become a fight and go.

However, the size and structure of the plastic can still be solved, because it is usually my (process/engineering) decision whether it will work or not. Anyway, if there is a functional problem in the future, I still need to be responsible. The most annoying thing is the appearance (cosmetic) problem., Because of the appearance problem, can you accept the wisdom of others? At this time, we must work with the quality control engineer to set the standard. When there are different colors of plastic parts, use a colorimeter, and then measure what a, b, delta values, etc. Yes, but in the end, it’s just to be judged by the naked eye. It is decided by looking at it under the fluorescent lamp and the sunlight, because sometimes the difference in the value is very small, but it looks uncomfortable~

As for scratches and stains, the specifications will also be set. Scratch defines how deep, wide, and long the scratch is; if it is a stain, define the diameter, number of points, and distance of the stain; the more troublesome part is the biting part, and the biting problem usually occurs when the plastic is shot. After time, the pattern of the bite will gradually blur or fade. Generally, we will make samples, and then sign the samples with the engineers of the relevant departments. When there is a problem, we will compare the samples with the signed samples.

At that time, there was a more interesting question, that is, "burr" in English. I have always wondered why the burr of metal parts is called burr, while the burr of plastic is called flash. At that time, I always felt that flash means flash. Is it right to use metal burrs? Later, a colleague told me that in the beginning of human history, there was no metal and plastic processing. The original English of burr means "thorn fruit", which means that plants have thorny fruits. Later, the industry developed, and metal processing products began to appear. When people found that there were burrs on metal objects that resembled thorns, they put metal The burr on the upper part is called burr. Later, the plastic part appeared. In order to distinguish the difference between the two, the plastic burr was called flash. This is the answer someone told me, and I don't know if it is true.

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