倒装芯片塑料球栅阵列封装器件在外应力下的失效机理

Failure mechanism of FC-PBGA devices under external stress

倒装芯片塑料球栅阵列(FC-PBGA)封装形式独特而被广泛应用,分析研究其在实际应用过程中,在高温、电、水汽等多种综合环境应力条件作用下的失效机理对提高其应用可靠性有重要意义.本文对0.13μm 6层铜布线工艺的FC-PBGA FPGA器件,通过暴露器件在以高温回流焊过程中的热-机械应力为主的综合外应力作用下的失效模式,分析与失效模式相对应的失效机理.研究结果表明,FC-PBGA器件组装时的内外温差及高温回流焊安装过程中所产生的热-机械应力是导致失效的根本原因,在该应力作用下,芯片上的焊球会发生再熔融、桥接相邻焊球致器件短路失效;芯片与基板之间的填充料会发生裂缝分层、倒装芯片焊球开裂/脱落致器件开路失效;芯片内部的铜/低κ互连结构的完整性受损伤而影响FC-PBGA器件的使用寿命.

Flip chip plastic ball grid array （FC-PBGA） is unique and has been widely used. During FC-PBGA＇s practical application, the analysis of its failure mechanisms under high temperature, electricity, water vapor and other comprehensive environmental stress conditions is very important for improving its application reliability. In this paper, with 0.13-μm/6-level copper-based FPGA with FC-PBGA package, failure mode of the device is exposed under external stress, which is dominated with thermal-mechanical stress generated by high temperature thermal reflow process. And the failure mechanism corresponding to the failure mode is analyzed. Results show that the basic cause of the failure is the thermal-mechanical stress, which is induced by the combination of internal and external reflow temperature difference and high temperature reflow process when assembled. The thermal-mechanical stress makes the solder bumps on the flip chip melt again and bridges the adjacent solder bumps to lead to the device short failure. It also induces crack or delamination in the underfill, crack in solder bump or solder bump fallen off to lead to device open failure. The residual stress on Cu/low-k interconnect structures damages the structure integrity and affects the reliability of FC-PBGA packages.