The purpose of this paper is to study the variation of the mechanical strength and failure modes of solder balls with reducing diameters under conditions of multiple reflows.,The solder balls with diameters from 250 to 760 µm were mounted on the copper-clad laminate by 1-5 reflows. The strength of the solder balls was tested by the single ball shear test and pull test, respectively. The failure modes of tested samples were identified by combing morphologies of fracture surfaces and force-displacement curves. The stresses were revealed and the failure explanations were assisted by the finite element analysis for the shear test of single solder ball.,The average strength of a smaller solder ball (e.g. 250 µm in diameter) is higher than that of a larger one (e.g. 760 µm in diameter). The strength of smaller solder balls is more highly variable with multiple reflows than larger diameters balls, where the strength increased mostly with the number of reflows. According to load-displacement curves or fracture surface morphologies, the failure modes of solder ball in the shear and pull tests can be categorized into three kinds.,The strength of solder balls will not deteriorate when the diameter of solder ball is decreased with a reflow, but a smaller solder ball has a higher failure risk after multiple reflows. The failure modes for shear and pull tests can be identified quickly by the combination of force-displacement curves and the morphologies of fracture surfaces.

中文翻译：

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通过剪切和拉力试验研究缩径焊球的强度

本文的目的是研究在多次回流条件下直径减小的焊球的机械强度和失效模式的变化。将直径从 250 到 760 µm 的焊球安装在覆铜板上 1 -5 回流。分别通过单球剪切试验和拉力试验来测试焊球的强度。通过结合断口形貌和力-位移曲线来识别测试样品的失效模式。通过对单个焊球剪切试验的有限元分析来揭示应力并辅助故障解释。较小焊球（例如直径 250 µm）的平均强度高于较大焊球（例如760 µm 直径）。与大直径焊球相比，较小焊球的强度在多次回流时的变化更大，其中强度随着回流次数的增加而增加。根据载荷-位移曲线或断口形貌,锡球在剪切和拉力试验中的失效模式可分为三种。,当锡球直径随着回流而减小时,锡球的强度不会下降，但较小的焊球在多次回流后具有较高的故障风险。剪切和拉力试验的失效模式可以通过力-位移曲线和断裂面形态的组合快速识别。根据载荷-位移曲线或断口形貌,锡球在剪切和拉力试验中的失效模式可分为三种。,当锡球直径随着回流而减小时,锡球的强度不会下降，但较小的焊球在多次回流后具有较高的故障风险。剪切和拉力试验的失效模式可以通过力-位移曲线和断裂面形态的组合快速识别。根据载荷-位移曲线或断口形貌,锡球在剪切和拉力试验中的失效模式可分为三种。,当锡球直径随着回流而减小时,锡球的强度不会下降，但较小的焊球在多次回流后具有较高的故障风险。剪切和拉力试验的失效模式可以通过力-位移曲线和断裂面形态的组合快速识别。