Thermal Reliability Of Low-silver Lead Free Ball Grid Array (BGA) Solder Joints

With the popularity of portable electronic products,the size of the solder joint decreases gradually.High Sn content and the high interconnect temperatures causing the growth of intermetallic compound?IMC?lead the reliability of the lead-free solder joints for electronics packaging because of the Pb-containing solder restricted to use.Among the lead-free solder,the low silver SAC lead-free solder has a good toughness,the good performance of anti-drop and thermal shock resistance and low cost of raw materials and so on,which is favored by domestic and foreign scholars.Therefore,systematic study of the reliability of low silver lead-free solder has important scientific significance on the development and application of low silver lead-free solder.The interfacial IMC growth evolution and analysis of solder joints reliability and failure mode of the low AgSn-0.45Ag-0.68Cu/ Cu solder joints under thermal cycling,thermal shock and thermal aging were investigated.The performance of low-Sn-0.45Ag-0.68 Cu silver lead-free solder by adding trace elements were also analysis.The results showed as follow:?1?During thermal shock and thermal cycling,the thickness of interface?Cu,Ni?₆Sn₅ IMC layer of the low Ag SAC / CuBGA solder joints increased constantly,and its morphology chang from a slender scallop-shaped to be gradually smooth,and the loose microstructure of IMC became more dense.At the same time,the shear strength and tensile strength of the solder joints showed a declining trend and both the shear and tensile fracture is the mode of the ductile fracture Compared with SAC305 / Cu solder joints,low Ag Sn-0.45Ag-0.68 Cu / Cu solder joint has its comparable reliability under thermal shock.?2?The interface?Cu,Ni?₆Sn₅ IMC layer of low silver SAC / CuBGA solder joints thickened constantly after thermal aging,and its morphology gradually from wavy to zigzag,and tending to smooth.At 100 ?,125 ? and150 ?,the growth factors of the IMC layer BGA solder joints were 5.88×10-19 m²/s,10.68×10^-19m²/s and 39.34 × 10-¹⁹m²/s,respectively.The activate energy of the IMC growth was49.41 k J/mol.With the increase of aging time,the shear strength and tensile strength had the trend of the downward,and the mechanical properties of solder joints decreased rapidly at high temperatures.?3?Thermal shock had the largest effect on the shear strength,tensile strength and layer growth rate of interface?Cu,Ni?₆Sn₅ IMC of low silver SAC / Cu solder joints,followed successively by thermal cycling and thermal aging.Comparative analysis of the influence of Co-P and Cu plating pad on the IMC growth of BGA solder joints,and evaluated the reliability of lower silver Sn-0.45Ag-0.68 Cu/Co-P BGA solder joints after thermal aging at 100 ? and150 ? as well as the comprehensive analysis the failure modes of the solder joints,the results showed that Co-15% P coatings on low silver solder Sn-0.45Ag-0.68Cu had good wetting properties at 250 ?.After thermal aging,the thickness of the interface CoSn₃ IMC layer of the low silver SAC/Co-P BGA solder joints had the overall increasing trend,and the?Cu,Co,Ni?₆Sn₅ IMC continued to gather to interface of the solder jointss to cause the organization coarsening.After long time aging,failure modes of the shear and tensile fracture were a mixed of toughness and brittle mode.Compared with the low silver SAC / Cu solder joints,low silver SAC /Co-P solder joints still had relatively advantage in long-term reliability.