Development of Micro-displacement and low-load fatigue tester and fatigue-strength estimating method for micro structures

随着对高贴装密度要求的不断提高，BGA(球栅阵列)或CSP(芯片尺寸封装)焊接成为电子贴装技术的主流。因此，评估BGA焊点的疲劳寿命是研究BGA封装可靠性的重要问题之一。本研究开发了一种微结构微位移低载荷疲劳试验机。利用该试验机对BGA CSP焊点的疲劳寿命进行了研究，建立了疲劳可靠性评估方法。(1)提出了一种适用于BOA、CSP焊点等微结构疲劳试验的试验机，该试验机采用PZT作为主推拉驱动器，双PZT用于无位错载荷测量。(2)基于提出的概念，研制了一种新的疲劳试验机。(3)利用该试验机对BGA CSP焊点的疲劳寿命进行了研究，并根据疲劳试验结果提出了一种对各种BOA焊点进行疲劳可靠性评估的方法。此外，还进行了三维有限元分析，得到了与之相关的断裂参数--非弹性等效应变范围。在实验和分析结果的基础上，提出了焊点疲劳寿命的估算准则。

With the increasing need for high mount density, the BGA (Ball Grid Array) or CSP (Chip Size Package) soldering became the main trend of the electronics mount technology. As a result, the evaluation of the fatigue life of BGA solder joints is one of the most important problems to study the reliability of BGA packages. In this study, a micro-displacement and low load fatigue tester for the micro-structures was developed. Using the tester, the fatigue life of BGA CSP solder joints was studied, and fatigue reliability assessment method was established.The results of this study are shown as follows ;(1) A new testing machine suitable for fatigue testing for the micro-structures such as BOA or CSP solder joints was proposed, by utilizing a piezoelectric translator (PZT) for the main push/pull actuator and twin PZTs for measuring the load without dislocation.(2) Based upon the proposed concept, a new fatigue tester was developed.(3) Using this tester, the fatigue lire of BGA CSP solder joints were investigated, and the results of fatigue tests were used to develop a fatigue reliability assessment method for all kinds of BOA solder joints. Furthermore, three-dimensional FEA were carried out to get the associated fracture parameter, inelastic equivalent strain range. Based upon the experimental and analytical results, an estimation criterion for fatigue life of the solder joints was developed.