EMC-Induced Thermal Deformations and Residual Stresses in IC Packaging

• Main Authors: Wang Chih Tung, 王志棟
• Other Authors: M. Y. Tsai
• Format: Others
• Language: zh-TW
• Published: 2002
• Online Access: http://ndltd.ncl.edu.tw/handle/76072561309300281131

碩士 === 長庚大學 === 機械工程研究所 === 90 === EMC-induced thermal deformations and residual stresses in IC packaging are investigated experimentally, theoretically and numerically. A real-time Twyman-Green interferometry is used for measuring the out-of-plane deformations, while dynamic mechanical analysis (DMA) and thermo mechanical analysis (TMA) are for characterizing mechanical properties of epoxy mold compound (EMC). Experimental observations associated with numerical simulation and theoretical predictions are used for understanding the thermal deformations and residual stresses of IC packages due to EMC. The mechanical properties of EMC materials, including elastic modulus (E), glass transition temperature (Tg) and coefficient of thermal expansion (CTE) have been characterized by DMA and TMA experiments. It is shown that EMC materials must be fully cured so that the material properties can be stable for applications. The real-time Twyman-Green interferometry has provided the deformations of die/EMC bi-material structure after the molding process prior to post mold curing (PMC). It is shown that residual deformations are not equal at the in-plane (x-y) direction. The volume shrinkage of EMC would induce the stresses during the high temperature molding process, but its viscoelasticity effect relaxed these stresses during the PMC process. The experimental results have demonstrated that die/EMC bi-material structure reverse warp at high temperature and viscoelasticity effect of EMC relaxed some stresses after many times or a long period of time of solder reflow process. Due to the zero-stress shifting to the high temperature, the residual deformations of die/EMC bi-material structure increased 40 ﹪after cooling down to the room temperature. For mechanics verification by comparing with experimental, theoretical, and FEM results, the mechanics behaviors of die/EMC bi-material structure under thermal loads have been resolved during the manufacturing process. Because of the free edge effects due to material and geometry discontinuous, interlaminar shear stresses and peel stresses start to occur at the structural interface and near the free boundary. The uniform distributions of axial stress exist at the region ranging from x=0-0.75L at low temperature down to x=0-0.4L at high temperature. The max. warpage and axial stressess caused by unit temperature change were found at 155℃ to 165℃. Although these can be changed due to viscoelastic stress relaxation, but these should be taken into account especially under thermal shock loading