Yiyu Qian

Development of Cu-Sn intermetallic compound at Pb-free solder/Cu joint interface

Abstract The development of Cu–Sn intermetallic compound (IMC) at the solder/Cu joint interface had been studied using two Pb-free solders, Sn–3.8Ag–0.7Cu and Sn–2Ag–0.8Cu–0.6Sb alloys. Meanwhile, 100Sn/Cu joint was applied for comparison. Both Pb-free solder joints were found with thinner Cu–Sn IMC layers at as-soldered state due to the slower dissolution rate of intermetallic compound into the liquid Pb-free solders during reflow and, consequently, slower growth rates of Cu–Sn IMC during the solid-state thermal aging at 125 °C, where Sn–2Ag–0.8Cu–0.6Sb solder joint gave the minimum value. Thermodynamic analysis showed that such phenomena could be attributed to the reduction of the driving force for Cu–Sn IMC formation due to the existence of Ag and Sb atoms.

The influence of dwell time on reliability of SMT solder joints under thermal cycling

Abstract The influence of dwell time on mechanical behaviour and fatigue life of SMT solder joints under thermal cycling has been investigated. The dwell time has two effects on the mechanical behaviour of SMT solder joints under thermal cycling: first, in the dwell time of high-temperature part, the stress in SMT solder joints will notably relax, and secondly, as the dwell time increase, the stress in solder joints in the low-temperature part of thermal cycling increases. With the increase of dwell time, the life of SMT solder joints under thermal cycling exponentially decreases.

Strengthening Sn60–Pb40 solder alloy by adding trace amount of La

Abstract The high temperature tensile strength of traditional Sn60–Pb40 solder alloy has been increased by 70% by adding trace amount of rare earth element La into it. Meanwhile, the thermal fatigue life of solder joints has been increased by two times. Such improvement is attributed to the modification effect of La on the microstructure of Sn60–Pb40 alloy.

A dislocation model of shear fatigue damage and life prediction of SMT solder joints under thermal cycles

Abstract In this paper, a damage model of low-cycle shear fatigue has been developed in the dislocation theory. On the basis of this model, a formula including the factors of thermal cycle temperature, dwell time and atmospheric oxidation has been established to predict the life of SMT solder joints under thermal cycles, and this has been verified by experiments on the specimens of true SMT assemblies. The results show that the life formula established in this paper coincides with the experimental results.

A study of the rheological behaviour of SnPb solders under varying temperature

Abstract An integral constitutive equation for one-dimensional shearing deformation of a soldered joint under varying temperature has been established based on viscoelasticity theory, and this has been verified by experiments on a sample subjected to simulated loading by thermal expansion. The theoretical results coincide well with the experimental ones. An important application of this integral constitutive equation is in the analyzing of the mechanical behaviour of the soldered joints in surface mount technology (SMT) under thermal cycling. An example of analyzing the relationship between stress and temperature in a SMT soldered joint under thermal cycling is also given.

Residual clad formation and aluminum brazed joint topology prediction

A method for aluminum brazed joint topology prediction based upon the observation of residual clad formation has been proposed in this work. It was found that the residual clad layer had a uniform topology regardless of brazing profiles. Therefore, the consumed clad mass, which flowed into the brazed joint during brazing process and is essential for brazed joint topology prediction, could be indirectly calculated upon the measured residual clad thickness and the mass conservation principle. Based on such obtained consumed clad mass and the principle of minimum potential energy, the aluminum brazed joint topology had been predicted and the results are in good agreements with the experimental data.

Indentation Rate-Dependent Creep Behavior of Sn-Ag-Cu Pb-Free Ball Grid Array (BGA) Solder Joint

Berkovich micro-indentation tests with different loading rates have been performed on the ball grid array solder joint with a Pb-free solder, Sn-4.0Ag-0.5Cu alloy. The resulting indentation load-depth curves are rate dependent and have varying creep penetration depths during the same hold time. Creep indentation hardness and rate sensitivity have been defined from the concept of “work of indentation”. The rate sensitivity of BGA solder joint is 0.0574.