Proposal of experimental method on fatigue of bonding materials for electronic packaging

Various bonding materials have been developed for power semiconductor products. However, the fatigue characteristics of many of these materials are difficult to evaluate uniformly using a conventional test, and this difficulty represents an obstacle to ensure proper material selection. In this report, we developed a new experimental method that can evaluate the fatigue properties of thin bonding layers. The conclusions of this report are shown below. (a) In developed method, the specimen with bonding layer is subjected to a two-way, four-point bending load. This method enables an evaluation even for a bonding material that can form only a thin layer. Furthermore, our method enables carrying out a fatigue test without any additional deformation even when substantial creep or ratchet deformation occurs in the bonding material. The high-speed examination is also possible to obtain high-cycle fatigue strengths. (b) We conducted a fatigue test on a Sn3.5Ag0.75Cu solder bonding layer. The results were that the fracture mode was good agreement with an actual joining structure. Moreover, the fatigue life obtained by our method in this test range followed the Coffin-Manson rule with high accuracy. (c) We found the relationship between the strain of bonding layer and the fatigue life using finite element analysis. The result was that the fatigue life curve of bonding layers was good agreement with that of bulk materials.