Abstract :
In solder ball grid array (BGA) technology, solder joint reliability is one of the critical issues in microelectronics manufacturing industries. In this reliability aging study, Sn3.5AgO.7Cu solder joints were subjected to accelerated temperature cycling (ATC) test in TBGA assembly. Fatigue fracture occurred, very close to the solder/intermetallic compound (IMC) interface, at the TBGA component side due to the larger coefficient of thermal expansion (CTE) mismatch compared to the PCB side. During reflow, needle-type and scallop-type morphologies of (Cu,Ni)6Sn5 IMCs were formed at the TBGA component and PCB interfaces. In the process of thermal cycling, a layer of (Ni,Cu)3Sn4 IMC grew beneath the (Cu,Ni)6Sn5 IMC due to the out diffusion of Ni from the under bump metallization (UBM). After extended thermal cycling aging, Ni-Sn-P IMC was found between the (Ni,Cu)3Sn4 IMC and the In3P layer at the printed circuit board (PCB) interface. Grain ripening and spalling of (Cu,Ni)6Sn5 IMC grains into the solder joint was also observed in the process of thermal cycling. The spalling phenomena of (Cu,Ni)6Sn5 IMCs was caused by interface structure change and cyclic shear stresses and strains incurred during temperature cycling.
Keywords :
ageing; ball grid arrays; copper alloys; fatigue; fracture; integrated circuit reliability; interface structure; metallisation; printed circuit testing; shear strength; silver alloys; soldering; solders; thermal expansion; tin alloys; (CuNi)6Sn5; (NiCu)3Sn4; ATC test; BGA technology; PCB interface; SnAgCu; TBGA assembly; accelerated temperature cycling; ball grid array; bump metallization; microelectronics manufacturing industry; printed circuit board; solder joint reliability; thermal cycling aging effect; Accelerated aging; Assembly; Electronics packaging; Fatigue; Life estimation; Microelectronics; Soldering; Temperature; Testing; Tin; Intermetallic compound (IMC); Pb-free solder; thermal cycling loading;
