Abstract
This paper discusses the microstructure evolution of copper (Cu) and gold (Au) ball bonds after various extended reliability stresses such as biased highly accelerated temperature and humidity test (HAST), unbiased highly accelerated temperature and humidity test (UHAST), temperature cycling (TC), and high temperature storage life (HTSL) in BGA package. Objective of this study is to study the microstructure evolution and changes after long hours and long cycles of component reliability stressing and its predicted failure mechanisms and to determine the long-term reliability comparison with combination of bonding wires in HAST, UHAST, and TC. Secondary electron microscopy (SEM) and energy dispersive X-ray (EDX) have been carried out to understand the respective microstructure of failed samples in HAST, UHAST, TC, and HTSL long-term reliability failures. Respective failure mechanisms of copper and gold ball bonds carrion under HAST and UHAST, ball bond lifting in TC and HTSL have been analyzed and proposed. The evolution of surface morphology, including copper and gold ball bond micro cracking, gold ball bond Kirkendall microvoiding and intermetallic compound (IMC) formation, was studied in FBGA package with copper and gold ball bonds during various reliability stresses. Biased HAST, UHAST, TC, and HTSL mechanisms were proposed to explain the observed morphological changes and the resulting ball bond wear out modes after extended reliability stresses. Weibull reliability analyses have been established to compare the performance of copper and gold ball bonds under humid and dry environmental tests.
Highlights
Gold and copper wire bondings are two most common bonding techniques used in microelectronic packaging in semiconductor industry
Au-Al microstructure evolution and intermetallic compound (IMC) formation is widely studied by Karpel et al [12]
We found CuAl IMC full separation and microcracking along beneath Cu ball bonds at the edge and center regions of CuAl IMC
Summary
Gold and copper wire bondings are two most common bonding techniques used in microelectronic packaging in semiconductor industry. Two types of failures occurred during annealing: crack formation at the bond periphery due to an increase in volume during intermetallic growth and the formation of stresses; and oxidation of the AlAu4 phase adjacent to the Au ball, which resulted in the formation of continuous cracks between the Au ball and the intermetallic region [10]. Drozdov et al [13, 14] evaluated CuAl IMC formation on as-bonded stage and post annealing to study the interface composition and morphology of copper wire bonds heat-treated at 175 °C for 2, 24, 96, and 200 h in argon. Void formation at the Al–Cu bonds heat-treated up to 200 h was not found to be a source of bond failure. Xu H et al [16, 17] characterized behavior of aluminum oxide, intermetallics, and voids in
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