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首页> 外文会议>EPP-vol.6; American Society of Mechanical Engineers(ASME) International Mechanical Engineering Congress and Exposition; 20061105-10; Chicago,IL(US) >Effect of Dwell Times and Ramp Rates on the Thermal Cycling Reliability of Pb-free Wafer- Level Chip Scale Packages - Experiments and Modeling
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Effect of Dwell Times and Ramp Rates on the Thermal Cycling Reliability of Pb-free Wafer- Level Chip Scale Packages - Experiments and Modeling

机译：停留时间和升温速率对无铅晶圆级芯片级封装热循环可靠性的影响-实验和建模

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Lead-free (Pb-free) solder has seen increasing use in interconnect systems for electronic packages due to legislative and marketing pressures. The NEMI selected eutectic Sn3.9Ag0.6Cu alloy (or a close variation near eutectic Sn3.5Agl.Ocu used in this study) is a leading Pb-free substitute for the Sn/Pb solder candidate. The reliability of this Pb-free solder alloy under accelerated thermal cycling and thermal shock testing as a function of testing parameters such as dwell time and ramp rate is critical in qualifying the performance of these Pb-free alternatives with the traditionally used Sn37Pb solder This paper presents the reliability of Pb-free solder joints in wafer level chip scale packages (WLCSPs) , which are extensions of flip-chip packaging technology to standard surface mount technology, with external dimensions equal to that of the silicon device [1]. The reliability of these packages under both liquid-to-liquid thermal shock (LLTS) testing and accelerated air-to-air thermal cycling (AATC) conditions, as a function of dwell times and ramp rates is evaluated using extensive experimental testing in combination with finite element analysis. Besides, two asymmetric cycles in which the cold and hot dwell times differ at two temperature extremes were studied. Along with the Pb-free solder, some test vehicles were built using eutectic Sn-Pb solder and evaluated for comparison purposes. Experimental results show that an increase in ramp rate does not adversely affect the solder joint reliability in the case of Pb-free solder. The reliability of lead-free WLCSPs was highly dependent upon the dwell time at the temperature extremes, with this dependency being considerably greater for the lead-free alloy than for Sn/Pb at 0℃ and 100℃. Accelerated test results show that increasing the dwell time from 280 to 900 seconds reduced the N_(63.2) of the Sn/Pb samples by 12% and the Pb-free samples by 65%. Reliability during asymmetric cycles resulted in a trend that is similar in two cases studied. A predictive equation was developed to evaluate the characteristic life of the package with respect to the dwell time. Non-linear, finite element (FE) modeling was conducted using temperature dependent creep constitutive relations for the Pb-free solder to understand the experimental trends observed. The FE results predicted the same trend of the package reliability as observed experimentally, with respect to the changing dwell and ramp times. The finite element predictions demonstrated reasonable correlation with the experimental observations.
机译：由于立法和市场压力，无铅（Pb）焊料已在电子封装的互连系统中得到越来越多的使用。 NEMI选择的低共熔Sn3.9Ag0.6Cu合金（或本研究中使用的低共熔Sn3.5Agl.Ocu附近的紧密变化）是替代Sn / Pb焊料的领先无铅替代品。这种无铅焊料合金在加速的热循环和热冲击测试下作为测试参数（例如停留时间和升温速率）的函数的可靠性对于用传统使用的Sn37Pb焊料验证这些无铅替代品的性能至关重要。提出了晶圆级芯片规模封装（WLCSP）中无铅焊点的可靠性，这是倒装芯片封装技术到标准表面贴装技术的扩展，其外部尺寸等于硅器件的尺寸[1]。这些封装在液-液热冲击（LLTS）测试和加速的空-空热循环（AATC）条件下的可靠性，作为保压时间和升温速率的函数，结合广泛的实验测试和有限元分析。此外，研究了两个不对称循环，其中在两个温度极限下冷和热的停留时间不同。除无铅焊料外，还使用了共晶Sn-Pb焊料制造了一些测试工具，并进行了比较评估。实验结果表明，在无铅焊料的情况下，斜率的增加不会对焊点可靠性产生不利影响。无铅WLCSP的可靠性高度依赖于极端温度下的保压时间，在0℃和100℃时，无铅合金的这种依赖性远大于Sn / Pb。加速的测试结果表明，将停留时间从280秒增加到900秒，使Sn / Pb样品的N_（63.2）降低了12％，而无铅样品的N_（63.2）降低了65％。在不对称循环中的可靠性导致在两个研究案例中的趋势相似。开发了一个预测方程式，以评估包装相对于停留时间的特征寿命。使用无铅焊料的温度相关蠕变本构关系进行非线性有限元（FE）建模，以了解观察到的实验趋势。有限元分析结果表明，对于改变的停留时间和斜坡时间，封装可靠性的趋势与实验观察到的趋势相同。有限元预测显示出与实验观测值合理的相关性。

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