纳米银焊膏热烧结及通电热老化过程动态电阻监测研究

Dynamic Resistance Monitoring of Nano Silver Paste during Sintering and Thermoelectric Aging Process

由于纳米银焊膏优异的导热性和导电性,使其在第三代半导体封装中受到了极大关注,其中,焊点的长期服役可靠性问题一直是封装领域的研究热点。提出焊点动态电阻在线监测方法,建立相应实时监测系统,将电阻转换为电阻率,研究电阻率在烧结和通电热老化过程中的变化情况,并对上述两个过程的焊点显微组织演变进行分析,建立电阻率变化规律模型。试验结果表明:在烧结过程中焊点电阻率逐步下降,且变化分为三个阶段。第一阶段,保温时间较短,焊点内未形成有效互连,电阻率极高;第二阶段,纳米银颗粒之间开始形成烧结颈,电阻率大幅下降;第三阶段,烧结颈长大,且焊点内有机物挥发完全,电阻率进一步下降。在通电热老化过程中,电阻率变化分为四个阶段。第一阶段,由于温度升高,材料电阻率随温度上升;第二阶段,焊点在高温下发生致密化行为,使电阻率下降;第三阶段,致密化过程基本结束,电阻率保持稳定;第四阶段,在电迁移效应影响下,银原子由阴极向阳极迁移,导致阴极附近出现裂纹,电阻率大幅上升直至焊点断路失效。

Due to the excellent thermal and electrical conductivity of nano-silver solder paste,it has attracted great attention in the packaging of third-generation semiconductors.Research on long-term service reliability of solder joints has always been a hot spot in the electronic packaging field.An in-situ dynamic resistance monitoring method is presented by a self-built corresponding real-time monitoring system.The resistivity(calculated from resistance)of silver paste joints are in situ monitored during the sintering process and the thermoelectric aging process.Moreover,by analyzing the corresponding microstructure and morphology evolution process of solder joints,a resistivity change model is established.The results show that the resistivity of the solder joint gradually decreases during the sintering process,and the change can be divided into three stages.In the first stage,the holding time is so short that no effective interconnection is formed in the solder joint,and the resistivity is extremely high.In the second stage,sintered necks are formed between the silver nanoparticles,and the resistivity decreases dramatically.In the third stage,the sintering necks grow,and the organics in the solder joints are completely volatilized,resulting in the gradually decrease of resistivity.In the thermoelectric aging process,the resistivity change can be divided into four stages.In the first stage,the resistivity rises with temperature.In the second stage,the densification behavior of the solder joint at high temperature causes the decrease of resistivity.In the third stage,the densification process is nearly completed and the resistivity remains stable.In the fourth stage,under the influence of the electromigration effect,silver atoms migrate from the cathode to the anode,resulting in cracks near the cathode,and the resistivity increases significantly until the solder joint fails.