探讨ADC芯片引脚与印制板之间的固封方式

Discussion on the Consolidated Mode Between ADC Lead Foot and PCB

通过故障分析,将某产品高温老炼试验过程中发生的性能异常现象定位于ADC芯片部分引脚焊点脱焊。为验证芯片引脚与印制板之间的固封方式对焊点受力的影响,分别对"底部灌封+四角固封"及"底部灌封+四边固封"固封方式进行试验验证及随机振动、热应力分析。根据分析结果,高温浸泡时"底部灌封+四边固封"方式下,焊点受力均匀,最大热应力低于3MPa;而"底部灌封+四角固封"固封方式下的焊点最大热应力约5.1MPa,导致了焊点的蠕变疲劳失效。为减少高温浸泡时焊点的热应力,设计了"底部不灌胶,四边固封但一角不封口"的固封方式,并顺利通过相应的验证试验,证明这是一种较为妥当的固封方式。

Based on the fault analysis, performance anomaly of a device which detected during the burn in experiment is located in the solder joint failure of ADC chip. Two consolidated mode, “bottom potting with four edges consolidated” and “bottom potting with four corner consolidated”, are experimented and analyzed to validate the difference of solder joint stress. With use of the first consolidated mode, maximum value of thermal stress is under 3MPa. Otherwise, with use of the second consolidated mode, maximum value of thermal stress is about 5.1MPa, as a result, the creep fatigue of solder joint take place. Aim to reduce the thermal stress of solder joint during the burn in experiment, a new consolidated mode describe as “bottom without potting, four edges consolidated with non seal for a corner” is designed. The new consolidated mode has passed the verification test all right which proved the new consolidated mode is felicitously.