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

PCB quality MRB meeting and plastic parts quality judgment at the manufacturing plant

I remember that when I first came into contact with a PCBA processing plant as a product engineer, I often needed to participate in MRB (Material Review Board) meetings, and I was also escorted from time to time to judge whether some rejected parts can be used waive, otherwise the production line would be There will be the danger of material interruption and line stoppage, and few people can afford the loss of line stoppage. 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: The MRB (Material Review Board) is usually composed of the PCB manufacturers' distribution, planner, quality, and process units. The purpose is to discuss and solve various problems in production. Miscellaneous diseases.

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 when marking the dimensions, and some will also 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 they are functional. Problem, sometimes you have to communicate the size tolerance with the design engineer. If there is enough time and ability, these issues should be raised at the stage of DFM (Design For Manufacture) review before mass production. However, as the pre-production industry for products is getting shorter and shorter, many people will excuse that time is tight., Ignoring these pre-jobs, consciously or unconsciously, turned into 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 is OK or not. Anyway, I will be responsible for functional problems in the future. The most annoying thing is the appearance (Cosmetic) The question is whether it is acceptable to see the wisdom of others because of the appearance problem. At this time, we must work with the quality control engineer to set the standard. When there are plastic parts of different colors, use a colorimeter, and then measure the a, b, and delta values. It's kind of, but in the end it's just the naked eye to judge it. It is decided by looking at it under fluorescent light and sunlight, because sometimes the difference in value is very small, but it looks uncomfortable.

As for scratches and dirty, the specifications will also be set. Scratch will define how deep, wide, and how 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 texture. The biting problem usually occurs After the plastic is injected for a period of 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 signed samples.

At that time, there was a more interesting question, that is, the English of "burr". I 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 was flashy. Meaning, it should be used on metal burrs, right? 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 exist. Appeared. When people found that there were burr-like edges on metal objects, they called the burr on the metal. Later, plastic parts appeared. In order to distinguish the difference between the two, they called the plastic burr flash. It’s the answer someone told me, and I don’t know if it’s true, but I think it’s acceptable!

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