Research On The Mechanical Properties Of Intermeallic Compound And Analysis Of Solder Joint Reliability In Electronic Packaging

With the lead-free and miniaturization of solder joints in electronic packaging, the intermetallic compound (IMC) which formed at the interface between the solder ball and under bump metallization(UBM) have considerable effects on the reliability of solder joints. In this paper, the mechanical properties of IMC were studied using nanoindentation. Based on which the effects of IMC on solder joint reliability under thermal cycling load and drop impact load conditions were researched by finite element simulation respectively.1. The nanoindentation was used to study the mechanical properties of every layer of lead-free solder and to test the IMC layers in the different working conditions. Compare the mechanical properties of the lead-free solder joints, the interfacial compound layer of IMC and the Cu pad, it showed that there are obvious differences between the IMC layer and the lead-free solder joint:the stress concentration occured around the IMC layers under the external loads, so the IMC layers become the key position of solder joint failure. Moreover, the different processing conditions (the composition of lead-free solder, the heating factor value and the number of reflow soldering) also have certain effects on the mechanical properties of IMC layers and it provides a research foundation for the further study of electronic products reliability.2. The elastoplastic constitutive equation of the IMC in electronic packaging can be obtained based on the nanoindentation test results. The nanoindentation process was simulated by the finite element analysis software ANSYS, and combining the dimensional analysis method and the inversion analysis technology, the link between the nanoindentation load-displacement curve and the material constitutive parameters was established. According to the concept of representative strain and representative stress, the elastoplastic constitutive models of IMC were obtained.3. Based on the thicknesses of IMC under different aging time, the effects of IMC thickness on the thermal fatigue reliability of solder joints were analyzed. The mechanical behavior of solder joints under thermal cycle loading were analyzed using finite element analysis software ANSYS. The finite element analysis software ANSYS was used to analyze the mechanical behavior of solder joints under the thermal cycle loading, and the Coffin-Manson’s empirical modified formula was used to predict the thermal fatigue life of solder joints. The main conclusions were as follows:the key solder joints were at the lower right of the chip where gets the maximum equivalent plastic strain values, and it is more likely to become invalid. Both the equivalent stress and the thermal fatigue life of critical solder joints decrease with the increasing of the IMC layers thickness. The thermal fatigue life of PBGA critical solder joint with19μm IMC thickness declines by21.46%than that with2μm IMC thickness. Lead-free solder Sn3.5Ag has the longest thermal fatigue life which is2.97times and1.33times of Sn0.7Cu and Sn3.0Ag0.5Cu respectively.4. The paper studied the influences of IMC layer thickness on the solder joint reliability under the drop impact loading and discussed the reliability of three different types of lead-free solder joints (Sn3.5Ag, Sn3.OAgO.5Cu and Sn0.7Cu) under drop impact loading. According to the JEDEC Standard JESD22-B111, ANSYS/LS_DYNA finite element analysis software and Input-G method were used to calculate the mechanical behavior of PBGA packaging under the conditions of board-level drop. The main conclusions were as follows: compared with the maximum peeling stress when the IMC layers thickness is0, the difference range of that is0.0314-0.1032GPa when the IMC layers thickness in the range of2-19μm, the corresponding increasing proportion is10.9%-36%. The maximum peel stress value of critical solder joint increases with the increasing of IMC layer thickness, and the increasing velocity declines gradually from0.0157GPa/μm to0.0009GPa/μm; meantime, the maximum peeling stress of Sn3.5Ag、Sn3.0Ag0.5Cu and Sn0.7Cu orderly increases from0.391GPa,0.326GPa to0.421GPa, which drawn a conclusion that Sn3.0Ag0.5Cu shows a better ability to resist deformation in the drop test.