Intermetallic compounds formation at interface between PBGA solder ball and Au/Ni/Cu/BT PCB substrate after laser reflow processes

This paper presents intermetallic compound formation at the interface between the Sn-Pb solder and the PBGA metallization (Au/Ni/Cu) substrate during a first laser reflow followed by a second infrared reflow processes. A thin layer of AuSn₄ was observed at the interface of solder joints, its morphology was strongly dependent on the laser reflow power and heating time applied. The AuSn₄ compound formed at the solder joint in the first laser reflow process also changed after the secondary infrared reflow process. To elucidate intermetallic formation mechanism at the interface, a finite element modeling (FEM) model is proposed, the simulated temperature profiles within the solder ball and at the solder-pad interface during laser heating are presented. In addition, the shear strength of the solder joints was tested, the correlation between the shear strength and their corresponding interfacial microstructure on the solder joints are also discussed.