Vibration fatigue of μBGA solder joint

摘要

This paper studies the vibration fatigue failure of μBGAsolder-joints reflowed with different temperature profiles, and ageingat 120° C for 1, 4, 9, 16, 25, 36 days. The effect of the thicknessof the Ni₃Sn₄ and Cu-Sn intermetallic compound(IMC) on the fatigue lifetime is also reported. During the vibrationfatigue test, in order to identify the failure of μBGA solder joint,electrical interruption was monitored continuously through thedaisy-chain network. Our results show that the fatigue lifetime of thesolder joint firstly increases and then decreases with increasingheating factor (Q_n), which is defined as the integral of themeasured temperature over the dwell time above liquidus (183° C) inthe reflow profile. The greatest lifetime occurs when Q_n isnear 500 s° C. Moreover, the lifetime of the solder joint decreaseslinearly with the increasing fourth root of the ageing time. The SEM/EDXinspection shows that only Ni₃Sn₄ IMC and Cu₆Sn₅/Cu₃Sn IMCs are formed between the solderand the nickel-plated PCB pad, and the solder/component-metallizationinterface respectively. For non-aged samples reflowed with differentprofiles, the fatigue crack generally initiates at valleys in the roughsurface of the interface of the Ni₃Sn₄ IMC withthe bulk solder. Then it propagates mostly near the Ni/solder, andoccasionally in the IMC layer or along the Ni/solder interface. For agedsamples, the fatigue crack mostly initiates and propagates in theCu₆Sn₅-phase/bulksolder interface or the Cu₃Sn/Cu₆Sn₅ interface oncomponent-metallization. Evidently, the intermetallic compoundscontribute mainly to the fatigue failure of μBGA solder joints. Thethicker the IMC layer, the shorter the fatigue lifetime of solder joint.The initial formation of the IMCs at the interface during solderingensures a good metallurgical bond between the solder and the substrate.However, a thick IMC layer influences the solder joint strength, whichresults in mechanical failure due to volume shrinkage during thetransformation from solid phase to the intermetallic compound