Abstract
SAC305 (Sn-3.0 %Ag-0.5 %Cu) BGA (ball grid array) solder joints were subjected to thermal cycling. As the number of thermal cycles increased, the thickness of IMCs (intermetallic compounds) increased accordingly. The interface evolutions of the BGA-chip and BGA-PCB (printed circuit board) interfaces were different. On the chip side, the main component of the IMCs was (Cu,Ni)6Sn5, which might form a fine network crack structure with the Ni layer under thermal stress. On the PCB side, Pb particles and the IMC Cu6Sn5 showed a weak ability to coordinate the relative deformation. Grain boundary cracks were easily generated at the BGA-PCB interface and developed into transcrystalline cracks, leading to a high failure rate.
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