유한요소해석을 이용한 Drilled Hole Cu필러범프 솔더접합부의 설계 및 열-기계적 신뢰성 평가

Abstract

In accordance with recent trends of miniaturized, multifunctional, and high-performance technology, considerable research has been conducted on finepitch flip-chip applications that use copper (Cu) pillar technology. The development of 3-dimensional (3D) packaging technology, such as the multi-chip package (MCP), the importance of certain technologies, such as a Cu pillar or through silicon via (TSV) technologies, has been highly noted. Some advantages of using these technologies is low latency, high performance, lower power consumption, increased bump density of the single footprint, and increased bandwidth due to short interconnections between semiconductor chips. CPB is a next-generation interconnect technology. The Cu pillar flip-chip interconnect has complications such as a lower mechanical strength and bridging between solder bumps due to a low standoff height compared to the conventional flip-chip interconnect. Nevertheless, CPB has many advantages, which enables a more aggressive die-to- package design rule or smaller package footprint. The extreme fine pitch on silicon package is lowered to 40 lm for TSV and chip-on-chip. Nonetheless, even these microelectronic packaging assemblies cannot avoid the issue of thermomechanical reliability. Owing to the aforementioned reasons, microelectronic packaging assemblies typically face thermal excursion that ultimately damages joints while packing structures are fabricated, assembled, and used. As a result, a coefficient of thermal expansion (CTE) mismatch occurs between various materials. To mitigate and resolve this issue, in this study, a hole was drilled in a CPB. Because the Drilled hole Cu pillar bump (DCPB) had a larger junction area than the original CPB, the ductile part of the solder, which was not covered by the intermetallic compound, was expected to block the spread of the crack, even if there was an initial crack. Moreover, a decrease was expected in the shearing stress while an increase was expected in solder quantity. This alteration in junction structure realistically has many more advantages than switching materials of the thermomechanical design. This is because an excessive amount of time and cost is required for switching materials, as it involves developing new materials and examining their properties of matter. Therefore, even though various materials may conflict, this study altered the junction structure of the CPB to increase its thermomechanical reliability. Accordingly, the elasto-plastic and viscoplasticity behaviors of the two structures were subsequently compared through finite element analysis. In particular, this study demonstrated thermo-mechanical characteristics through elasto-plastic analysis. Furthermore, this study applied the Anand model in order to verify viscoplasticity, which addresses both plastic strain and creep strain, as well as a submodeling technique to increase the accuracy of the analysis and decrease the analysis time. In addition, this study confirmed the superiority of the thermomechanical reliability of drilled Cu pillar bump (DCPB) through a hysteresis loop, which showed the equivalent stress versus equivalent inelastic strain of the solder joint interfaces. Moreover, the study compared the inelastic strain energy density values. The results demonstrated that the drilled copper pillar bump does indeed have a smaller inelastic range and a lower inelastic strain energy density.