散热强化型覆晶球栅数组组合体之锡球可靠度研究

An Investigation of the Solder Ball Reliability for a Thermally Enhanced FC-PBGA Assembly

摘要: 本文探讨之散热强化型覆晶球栅数组组合体是基本型覆晶球栅数组封装体包封着封胶，接着在封胶上面黏附着一片铝质散热板，最后以锡球构装在印刷电路板上。凸块与锡球是锡铅合金属于黏塑材料，在文中的数值模拟中，是以亚兰德模型来定义并描述其弹性、塑性及潜变行为，其余组件是假设为弹性材料。本文使用有限元素分析软件ANSYS建立一精确之三维有限元素模型，于温度循环负载下，针对此组合体并搭配修正型Coffin-Manson疲劳寿命估算式进行锡球可靠度分析。本文报告了锡球应力、应变及疲劳寿命等机械行为。最后，进行參数化分析，探讨组合体组件的设计参数对锡球疲劳寿命的影响。结果表明：增加基板基材的热膨胀系数、杨氏系数与厚度可以提高锡球疲劳寿命。减少散热板膨胀系数、杨氏模数、厚度与宽度也会造成锡球寿命增加。增加封胶热膨胀系数或减少封胶杨氏模数会造成锡球疲劳寿命增加。黏着剂所占的体积小对锡球疲劳寿命的影响很小。在本文之研究范围内，减少热膨胀系数、减少杨氏模数及增大厚度有助于提升锡球疲劳寿命。

Abstract: In this paper, the thermally enhanced FC-PBGA (Flip-Chip Plastic Ball Grid Array) assembly is a basic FC-PBGA package that is over-molded with molding compound, after which an aluminum heat spreader is adhered to the top of the molding compound and subsequently mounted on a PCB (Printed Circuit Board). Three-dimensional finite element analysis using the commercial ANSYS software is performed to study solder ball fatigue life for this thermally enhanced FC-PBGA as-sembly subjected to temperature cycling. In the simulation, all the solder bumps and the solder balls are modeled with nonlinear viscoplastic time and temperature dependent material properties based on Anand’s constitutive equation. Solder ball fatigue life is estimated by the widely accepted modified Coffin-Manson equation. The thermo-mechanical behavior of the assembly is pre- sented. Effects of alternative design parameters of the package components on solder ball fatigue life are analyzed. It is found that higher CTE of the substrate core, higher Young’s modulus of the substrate core, thicker substrate core, lower heat spreader CTE, lower heat spreader Young’s modulus, reduction of the thickness or width of the heat spreader, higher CTE of the molding compound and lower Young’s modulus of the molding compound result in better solder bump fatigue life. The effects of the parameters of the adhesive are found to have lesser impact on package reliability. However, lower CTE, lower Young’s modulus and greater thickness are found preferable.