Reliability study and failure analysis of fine pitch solder bumpedflip chip on low-cost printed circuit board substrate

摘要

The design and proper selection of low-cost printed circuit board(PCB) is essential to the reliability and formation of solder joints forthe fine-pitch solder-bumped flip-chip on board (FCOB) technology. Bynature low-cost PCBs don't have the precision in patterns like thefine-pitch solder-bumped flip-chip technology. In this study, eutecticsolder bumps (63Sn/37Pb) were electroplated on the test-chips withvarious pad pitches and chip sizes. Several types of low-cost PCBdesigns were evaluated for the fine-pitch solder-bumped flip-chip. Theeffects of different PCB designs on the formation and shapes of solderjoints were studied. The location and formation of voids in theunderfill depend on the design and properties of the PCB. The alignmentaccuracy of the solder mask opening area and the copper pad on the PCBis very critical for the reliability of FCOB technology. The acceptablemis-registration on the low-cost PCB decreases as the chip sizeincreases. Scanning acoustic microscope (SAM), X-ray imaging system,cross-sectioning, scanning electron microscopy (SEM) were used toevaluate and inspect the samples after the thermal cycling test andtemperature-humidity test. The solder joint failure modes after thermaltests were studied