导电胶在高温老化与温度冲击中的失效模式研究

06Research on failure mode of conductive adhesive under high temperature aging and temperature shock

针对我国航天领域使用较为广泛的HD-903型改性环氧树脂导电胶,本研究采用高温老化和温度冲击来加速导电胶在服役环境中的变化,从而对导电胶的可靠性展开研究。在试验过程中,通过对导电胶试样的形貌组织进行观察,并测量其体积电阻率和芯片剪切强度,通过其性能的变化来反映导电胶内在变化的规律。研究结果表明:在150℃下老化过程中,导电胶的体积电阻率先下降随后不断增加,同时芯片剪切强度先升高后下降。高温老化5000 h后体积电阻率相比老化前增加81.0%,芯片剪切强度为老化前的56.5%。温度冲击3000次后,导电胶的体积电阻率较试验前升高77.2%,芯片剪切强度仅为试验前的13.8%。分析认为,导电胶在高温老化中主要发生银粉的氧化和树脂基体的老化,一方面破坏银粉与树脂基体之间的界面结构,另一方面树脂基体的老化使其发生严重松弛,引起体积电阻率的大幅提高和胶体强度的下降。在温度冲击过程中,由于导电胶与芯片、可伐镀金基板的热膨胀系数存在差异,由此在交变应力载荷作用下引发粘接接头的蠕变和疲劳,先后在接头靠近芯片一侧和靠近基板一侧分别产生裂纹并逐渐扩展,最终造成接头强度的大幅度降低。

In response to the widely used HD-903 modified epoxy resin conductive adhesive in China′s aerospace industry,high-temperature aging and temperature shock were used in this study to accelerate the changes of the conductive adhesive in the service environment,thus conducting research on the reliability of the conductive adhesive.During the experiment,the morphology and organization of the conductive adhesive sample were observed,and its volume resistivity and chip shear strength were measured to reflect the inherent changes of the conductive adhesive through changes in its properties.The research results showed that during the aging process at 150℃,the volume resistance of the conductive adhesive first decreased and then continuously increased,while the shear strength of the chip first increased and then decreased.After 5000 hours of high temperature aging,the volume resistivity increased by 81.0%compared to before aging,and the shear strength of the chip was 56.5%of before aging.After 3000 temperature shocks,the volume resistivity of the conductive adhesive increased by 77.2%compared to before the test,and the chip shear strength was only 13.8%of before the test.Analysis suggested that conductive adhesive mainly underwent oxidation of silver powder and aging of resin matrix during high temperature aging.On the one hand,this destroyed the interface structure between silver powder and resin matrix.On the other hand,the aging of resin matrix caused severe relaxation,resulting in a significant increase in volume resistivity and a decrease in adhesive strength.During the temperature shock process,due to the difference in thermal expansion coefficients between the conductive adhesive and the chip,as well as Kovar gold-plated substrate,creep and fatigue of the adhesive joint were induced under alternating stress loads.Cracks gradually propagated on the side of the joint near the chip and the side near the substrate,resulting in a significant decrease in joint strength.