微波芯片倒装金凸点热疲劳可靠性分析及优化

Thermal Fatigue Reliability Analysis and Optimization of Flip-Chip Gold Bumps for Microwave Chip

为了满足射频系统小型化的需求,提出了一种基于硅基板的微波芯片倒装封装结构,解决了微波芯片倒装背金接地的问题。使用球栅阵列（BGA）封装分布为周边型排列的Ga As微波芯片建立了三维有限元封装模型,研究了微波芯片倒装封装结构在-55-125℃热循环加载下金凸点上的等效总应变分布规律,同时研究了封装尺寸因素对于金凸点可靠性的影响。通过正交试验设计,研究了凸点高度、凸点直径以及焊料片厚度对凸点可靠性的影响程度。结果表明：金凸点离芯片中心越近,其可靠性越差。上述各结构尺寸因素对凸点可靠性影响程度的主次顺序为：焊料片厚度〉金凸点直径〉金凸点高度。因此,在进行微波芯片倒装封装结构设计时,应尽可能选择较薄的共晶焊料片来保证金凸点的热疲劳可靠性。

In order to meet the requirement of radio frequency system miniaturization,a flip-chip package structure for the microwave chip based on silicon substrate was proposed,which solved the problem of microwave chip flip-back gold grounding. A three-dimensional finite element packaging model was established by using a ball grid array（ BGA） package with a peripherally arranged Ga As microwave chip.The distribution of the equivalent total strain sustained in the gold bumps of the flip-chip package structure of microwave chips under the thermal cycling load from-55 ℃ to 125 ℃ was studied. Meanwhile,the influences of the package size factors on the reliability of gold bumps were investigated. Through Orthogonal experimental design,the influence degree of bump height,bump diameter and solder sheet thickness on the reliability of bumps was studied. The results show that the closer the gold bump is to the chip center,the worse its reliability is. The effects of the structural size factors on the reliability of the bumps can be ranked as： solder sheet thickness gold bump diameter gold bump height. Therefore,in the microwave chip flip-chip packaging structure design,the thinner eutectic solder sheets should be selected as far as possible to ensure the thermal fatigue reliability of gold bumps.