Vibration fatigue of μBGA solder joint
2000 Proceedings. 50th Electronic Components and Technology Conference (Cat. No.00CH37070)
This paper studies the vibration fatigue failure of pBGA solder-joints reflowed with different temperature profiles, and ageing at 120°C for 1, 4, 9, 16,25, 36 days. The effect of the thickness of the Ni3Sn4 and Cu-Sn intermetallic compound (IMC) on the fatigue lifetime is also reported. During the vibration fatigue test, in order to identify the failure of pBGA solder joint, electrical interruption was monitored continuously through the daisy-chain network. Our results show that the fatigue
... that the fatigue lifetime of the solder joint firstly increases and then decreases with increasing heating factor (Q"), which is defined as the integral of the measured temperature over the dwell time above liquidus (1 83°C) in the reflow profile. The greatest lifetime occurs when Q, is near 500 SOC. Moreover, the lifetime of the solder joint decreases linearly with the increasing fourth root of the ageing time. The SEMEDX inspection shows that only Ni3Sn4 IMC and Cu6Sn5/Cu3Sn IMCs are formed between the solder and the nickel-plated PCB pad, and the solder/componentmetallization interface respectively. For non-aged samples reflowed with different profiles, the fatigue crack generally initiates at valleys in the rough surface of the interface of the Ni3Sn4 IMC with the bulk solder. Then it propagates mostly near the Nilsolder, and occasionally in the IMC layer or along the Nilsolder interface. For aged samples, the fatigue crack mostly initiates and propagates in the Cu6Sn5-phase/bulksolder interface or the Cu3Sn/Cu6Sn5 interface on componentmetallization. Evidently, the intermetallic compounds contribute mainly to the fatigue failure of pBGA solder joints. The thicker the IMC layer, the shorter the fatigue lifetime of solder joint. The initial formation of the IMCs at the interface during soldering ensures a good metallurgical bond between the solder and the substrate. However, a thick IMC layer influences the solder joint strength, which results in mechanical failure due to volume shrinkage during the transformation from solid phase to the intermetallic compound.