Thermal Defect Attribution Models for Mixed Consigned and Turnkey Boards
Thermal defect attribution in mixed consigned assembly requires combining profile logs, 3D X-ray data, and MSL handling records to split material and process liability.
Acceptable Quality Level
Rejection Threshold
Statistical standards establish the maximum number of defective boards permitted in a sampling batch during receiving inspection. Under standard PCB purchase contracts, the acceptable quality level defines the nonconformance percentage that triggers the rejection of an entire shipment. It establishes a boundary for acceptable process variation.
If the defect rate exceeds this threshold, the batch is returned to the fabricator.
Sampling Protocol
Receiving procedures dictate how random boards are extracted and measured. For high-reliability assemblies, the acceptable quality level determines both the sample size and the allowable failures within that set. Inspectors consult standardized tables to find the sample count based on lot size, such as examining eighty boards from a batch of one thousand.
A smaller level requires zero defects in a larger sample, raising the bar for the supplier. This prevents marginal boards from passing through into the manual SMT assembly lines where rework costs are high.
Operational Limit
Production contracts tie commercial penalties to these statistical bounds. When a lot is rejected under the acceptable quality level, the manufacturer must rework the boards or absorb the scrap cost. This distribution of financial risk forces tighter control on process lines.
It stabilizes yields across batches.