Failure Allocation
Root-cause investigations identify whether assembly board failures originate from incorrect oven temperature profiles or inherent material defects. Conducting thermal defect attribution allows process engineers to distinguish between soldering failures caused by incorrect reflow settings and those caused by substandard component finishes or board fabrication. This analysis prevents assembly houses from accepting liability for board failures when the fault lies with the component supplier.
It ensures that corrective measures are directed at the correct stage of the manufacturing process.
Reflow Analysis
Inspection data and metallurgical analysis are used to determine where the defect was introduced. For example, a voided solder joint might result from a reflow profile that heats the board too quickly, or it might result from contamination on the component lead. Process engineers analyze the shape and location of the solder joints to determine the thermal history.
This investigation often requires cross-sectioning the board to examine the intermetallic layer thickness under a microscope.
Corrective Action
Establishing the exact cause of a thermal defect prevents the recurrence of identical failures in subsequent production runs. Once thermal defect attribution points to a specific source, the assembly house can either adjust the oven profile or reject the suspect lot of components. In cases where the solder alloy has failed to wet the copper pads, a comparison between oven logs and the PCB manufacturer’s test coupons reveals the culprit.
If the oven settings were correct, the blame is attributed to the board fabricator’s poor surface finish. This clear demarcation of fault maintains high quality standards across the supply chain by holding each vendor accountable. Process logs are archived for several years to serve as legal evidence if a dispute arises between the contract manufacturer and the customer over warranty claims.
