A Study of Solder Joint Failure Criteria

One of the challenges in an experimental study of solder joint reliability is to determine when cracks occur in a solder joint or when a solder joint fails. Cracks in a real solder joint are difficult to identify using an X-Ray system. Cross-sectioning and scanning electron microscopy (SEM) is a destructive method. A common non-destructive test method is to monitor resistance increase in a solder joint or a daisy-chain. However, no scientific research has been done in establishing the relationship between the crack area of an interconnection and the change in resistance of the interconnection. This paper proposes a method of defining failure criteria as the resistance increase in a solder joint exceeding a threshold. The threshold is determined by k times the range over the natural variation in resistance measured by a measurement system. The natural variation by random cause is judged using X-bar and R charts. The principles of defining failure criteria are to be able to detect failure of solder joints as early as possible with minimum false detection due of measurement system error/variation. An experimental study confirmed that a full crack of an interconnection occurs when the increase of resistance in the interconnection is 10 times the natural variation of resistance change. The results of this study could be used to narrow the definition of failure in consensus standards IPC 9701A, JESD22-B111, and IPC/JEDEC-9702.