Bonding Defect
Workmanship defects occur when a metal surface fails to form a strong metallurgical bond with molten solder during the assembly process. A solderability failure is typically caused by contamination or oxidation of the surface finish on the pcb pads or component leads. The result is a weak or non-existent electrical connection that can lead to immediate test failure or long term reliability issues.
This failure often stems from improper storage conditions where exposure to sulfur or high humidity accelerates the growth of intermetallic layers before the board reaches the assembly line.
Pad Condition
Protective finishes such as osp or enig are applied to preserve the base copper from environmental factors. If these coatings are too thin or have been exposed to high humidity, they may not prevent the copper from oxidizing. This oxidation creates a barrier that the flux cannot easily remove, leading to a solderability failure where the solder beads up rather than spreading across the landing area.
Verification Testing
Dip and look tests or wetting balance scales are used to assess the quality of the surfaces before assembly begins. These tests measure the force and time required for the solder to wet the test sample. Identifying a potential solderability failure at the receiving stage prevents the loss of expensive components on a board that cannot be properly soldered.
