| At present, with the development of science and technology, informationtechnology became one of the most active productivity factors, play a dominant role inmany areas of technology. Brazing technology is key to product Assembly andpackaging of information technology, which is widely used in computers,telecommunications, household appliances, as well as in aviation, aerospace and otherhigh-tech areas. With the development of Electronics Assembly and packagingtechnology as well as increasing environmental pressure, the Sn-Pb solder alloyswhich was widely used in electronic products,gradually disappeared from the stage ofhistory because they can not meet the application requirements. The lead-free solderhas become an inevitable trend in the development of electronic products, leading tolead-free solder joint reliability issue has become a hot topic in modern brazingtechnology. After long-term research, people gradually realized that the phenomenonof creep fracture、fatigue fracture and electromigration failure are related with thesolder joint interfacial IMC, namely IMC is a key factor affecting the reliability oflead-free solder joints. Therefore, the studying of lead-free solder interface variation ofIMC growth is very necessary.Using the wide application of Sn-3.0Ag-0.5Cu lead-free solder as the researchobject, the effects of different brazing time on IMC growth is studied. The results showthat the average thickness of the interfacial IMC is increasing with the soldering timeincreases, while the unevenness of IMC at first increases and then tends to smooth; theinterfacial IMC grows faster in short soldering time; After60s,the grow rate ofinterfacial IMC tends to slow down, because the generated Cu6Sn5hinder heat andmass transfer between the liquid metal and Cu substrate.Based on the home-made in-situ observation device, the microstructures andgrowth law of Sn-3.0Ag-0.5Cu solder/Cu joint were investigated under110℃thermal exposure condition. The results shows that: the Cu3Sn appears between the Cu6Sn5and Cu substrate after soldering for120h; the thickness of IMC increases withthe soldering time increasing. At the same time, the growth of IMC haveThree-dimensional characteristics, the Cu6Sn5changes evident in the longitudinaldirection and reduces gradually, while changes slowly in in the transverse directionwith the aging time. The microstructures of IMC changes from the scallop shape into arelatively flat layer, and appears stratified phenomenon with the soldering timeincreasing.Based on the home-made multiphase field device, an investigation was carried onmicrostructure and growth of IMC at the interface between Sn-3.0Ag-0.5Cu lead-freesolder and Cu substrate in different temperature(150,125,85℃). The results show thatthe higher the aging temperature, the faster the IMC grow in the same aging time, andthe trend of IMC in line with parabolic law. During multiphase field aging at85,125and150℃up to400h, the initial scallop IMC layer changes into a plane shape; TheAg3Sn particles are found in the Cu6Sn5layer and always appear in Cu6Sn5cavity. TheIMC thickness is linearly proportional to the square root of aging time, which reveals adiffusion-controlled mechanism during aging. Multi-field coupling accelerate thegrowth rate of the IMC，through the fitted curve the diffusion coefficient at thetemperature of150,125,85℃is obtained respectively, which is D1=4.54×10-17m2/s,D2=1.23×10-17m2/s，D3=3.32×10-18m2/s；The activation energies of the total IMClayers growth reduced to49kJ/mol during the multiphase field aging. |
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