Abstract :
The effects of Sn diffusion, Ag and Pd dispersion and intermetallic compound growth on the shear fatigue of solder joints between thick film mixed bonded Pd-Ag conductor and 62Sn-36Pb-2Ag solder are investigated. The samples were prepared by assembling leadless ceramic chip carrier (LCCC) passive components on a 96% Al2O 3 substrate and ageing at 150°C for varying times. Microstructural analysis reveals that the intermetallic compounds (IMC) Pd3Sn2, Pd3Sn, Pd2Sn, PdSn, PdSn2, PdSn4, Ag5Sn, Ag3Sn, PbPd3, and Pb3Pd5 are formed after ageing. X-ray dot maps demonstrate that the longer the ageing time, the more serious the Ag and Pd dispersion into the solder and the Sn diffusion into the conductor. It is noted that the Sn diffuses to the interface of the substrate/conductor after 120 hours ageing. Shear strength tests at varying strain rates show that adhesion strength decreases with prolonged ageing time. Shear cycling tests indicate that the solder joint fatigue lifetime depends on the Ag and Pd diffusion range, and especially on Sn diffusion into the thick film conductor. These results mean that the more serious the Sn and Ag interdiffusion, and the more IMC is formed in the solder joint (which can be due to prolonged high temperature storage or long term operation of SMT assemblies), the more sensitive is the solder joint to stress, eventually leading to fatigue failure. It is argued that volume change and increased brittleness due to intermetallic formation, and conductor layer volume swelling due to Sn diffusion are major factors in the decrease of solder joint fatigue lifetime and shear strength
Keywords :
X-ray analysis; adhesion; ageing; brittleness; ceramics; chemical interdiffusion; crystal microstructure; fatigue; hybrid integrated circuits; integrated circuit packaging; integrated circuit reliability; mechanical testing; shear strength; soldering; surface mount technology; 120 hr; 150 C; 62Sn-36Pb-2Ag solder; Ag diffusion range; Ag dispersion; Ag interdiffusion; Ag3Sn; Ag3Sn IMC; Ag5Sn; Ag5Sn IMC; Al2O3; Al2O3 substrate; IMC; Pb3Pd5; Pb3Pd5 IMC; PbPd3; PbPd3 IMC; Pd diffusion range; Pd dispersion; Pd/Ag conductor; Pd2Sn; Pd2Sn IMC; Pd3Sn; Pd3Sn IMC; Pd3Sn2; Pd3Sn2 IMC; PdSn; PdSn IMC; PdSn2; PdSn2 IMC; PdSn4; PdSn4 IMC; SMT assemblies; Sn diffusion; Sn interdiffusion; Sn/Pb/Ag solder; SnPbAg-PdAg; X-ray dot maps; adhesion strength; ageing; ageing effects; ageing time; assembling; brittleness; conductor layer volume swelling; fatigue failure; high temperature storage; intermetallic compound growth; intermetallic compounds; intermetallic formation; leadless ceramic chip carrier passive components; microstructural analysis; shear cycling tests; shear fatigue; shear fatigue life; shear strength tests; solder joint; solder joint fatigue lifetime; solder joint shear strength; solder joints; strain rates; stress sensitivity; substrate/conductor interface diffusion; thick film mixed bonded Pd-Ag conductor; volume change; Aging; Assembly; Conductive films; Conductors; Fatigue; Intermetallic; Lead; Soldering; Thick films; Tin;
