Reliability of Ball Grid Array (BGA) Assembly with Reworkable Capillary Underfill Material

Abstract

In this paper, the reliability of the BGA assembly with underfill material is studied by three-point bend test, mechanical bending fatigue test and thermal fatigue test. With the rapid development of surface mount technology (SMT), ball grid array (BGA)/chip scale package (CSP) are widely used in portable electronic devices, such as phone, pager, and PDA. But to increase reliability of BGA/CSP is a big challenge to the application of these devices. One important method to improve reliability of BGA or CSP is underfilling technology. Therefore, the effect of reworkable capillary underfill material on reliability of BGA assembly needs to be investigated systematically. In this study, samples are reflowed with an optimized rpid ramp temperature profile. Then some samples are underfilled by two different reworkable capillary underfill materials. All three kinds of samples are divided into three groups respectively. One group of samples is subjected to three point bend load at normal temperature on the mini-mechanical testing. The second group of samples is subjected to mechanical bending fatigue load at a fatigue frequency of 60 cyclic per minute on mini-mechanical testing too. The third group of samples is subjected to thermal fatigue shock at temperature -40~+125degC, and the dwell time 20 min. Three point bend experimental results show that the reworkable capillary underfill material can improved the static mechanical reliability of BGA assembly. And the failure modes BGA assembly is also different with different underfill material. The mechanical bending fatigue experimental results show that the BGA assembly with two different reworkable capillary underfill exhibits higher mechanical bending fatigure reliability than that of the BGA assembly without any underfill materials. Thermal fatigue experimental results show that the thermal fatigue reliability of BGA assembly with U1 underfill material is lower than that of BGA assembly without any underfill material. The reliability of BGA assembly with U2 underfill material is higher than that of BGA assembly without any underfill material