During the raw material warehousing stage, the material code, batch number and MSL level must be checked synchronously. Special attention should be paid to whether the baking records of moisture-sensitive devices are complete and whether the time and temperature comply with Jia Jinyuan's internal standards; otherwise, the popcorn effect is highly likely to occur after placement. Before Solder Paste is issued for use, it must be confirmed that the warm-up time is no less than 4 hours and the paste is evenly stirred; otherwise, the poor release rate during printing will directly increase by more than 12%.

In the solder paste printing process, the stencil tension, squeegee pressure and speed must be dynamically matched. When the stencil tension is lower than 35N/cm, continuous solder insufficiency will occur on fine-pitch QFN pads. If the squeegee angle deviates from the range of 45°±2°, the solder paste thickness variation coefficient of 0201 component pads will exceed 15%. At this point, the line must be stopped immediately for calibration instead of merely wiping the stencil.

If the vacuum value of the placement machine nozzle is lower than -85kPa, component flying or offset will occur. We require three actual measurements with a standard block per shift and record the results. Meanwhile, check whether the feeding rhythm of the Feeder vibrating tray is synchronized with the placement cycle. Once material missing or jamming is found, the coordinate offset trend of the previous 100 NG boards must be traced; the problem cannot be solved simply by replacing the nozzle.

The reflow oven temperature profile must be actually measured for the first article every day. Key monitoring points include whether the peak temperature fluctuation exceeds ±2℃ and whether the time above the liquidus is maintained between 60 and 90 seconds. If the heating slope in a certain section suddenly changes by more than 3℃/s, the heating module's power supply voltage imbalance must be immediately investigated instead of simply adjusting the chain speed.

The AOI inspection program must be compared and verified with physical defect samples every week. In particular, the recognition threshold for BGA bottom voids is set at 25% rather than the 30% recommended in textbooks, because Jia Jinyuan's customer rejection standards have long been tightened. During X-RAY re-inspection, if more than 3 points in the same LOT have a void rate >18%, the entire batch must be placed under isolation review; it cannot be released just because sampling passes.

Finished product inspection should not only look at the functional test pass rate, but also retrieve the SPC data of the first three processes to check the trend. For example, when the printing thickness CPK falls below 1.0, even if the AOI false positive rate is low, the product cannot be judged as good. The viscosity change of the solder paste batch and the environmental temperature and humidity records must be traced backwards. The essence of SMT quality control has never been how many defects are caught at the final stage, but preventing defects from occurring in the first place.