Solder Joint Reliability & Prognostication of Lead Free Electronics in Harsh Thermo-Mechanical Environments

Abstract

The trends in the electronic packaging industry are to design smaller packages that have higher complexity, and to improve package reliability while reducing costs. These needs in the packaging industry have lead to a newer generation of chip architectures, such as: Chip Scale Packages, Plastic Ball Grid Arrays, and Flip Chips. However, despite the increased performance capabilities of these leading-edge package types, their thermo-mechanical reliability is a concern for harsh environment applications. In this study, the thermo-mechanical reliability of a new architecture (D-PackTM) has been studied using finite element methods. Life prediction relationships based on damage accumulation principles have been used to calculate the characteristic life, and has been compared with thermal shock data. Failure analysis of the tested assemblies has been conducted to correlate failure locations with predictions from FEM.

While reliability analysis of any component is critical, it is also important to monitor the condition / state of the system from time to time in order to improve the system availability and upkeep. So far, traditional health monitoring methodologies have relied on reactive methods of failure detection often providing little on no insight into the remaining useful life of the system. Detection of system-state significantly prior to catastrophic failure can significantly impact the reliability and availability of electronic systems. Previously, Lall [2004, 2005] have developed methodologies for health management and interrogation of system state of electronic systems based on leading indicators for eutectic Sn-Pb & 95.5Sn4.0Ag0.5Cu solders. Examples of damage pre-cursors include micro-structural evolution, intermetallics. In this study, a mathematical approach for interrogation of system state under cyclic thermo-mechanical and iso-thermal stresses has been developed for 4-different lead-free solder alloy systems. Data has been collected for leading indicators of failure for alloy systems including, SnAgCu, SnAgCuBi, SnAgCuBiNi, SnAg second-level interconnects under the application of thermo-mechanical loads. Methodology presented resides in the pre-failure space of the system in which no macro-indicators such as cracks or delamination exist. Systems subjected to thermo-mechanical damage have been interrogated for system state and the computed damage state correlated with known imposed damage. The approach involves the use of condition monitoring devices which can be interrogated for damage proxies at finite time-intervals. Interrogation techniques are based on non-linear least-squares methods. Various techniques including the Levenberg-Marquardt Algorithm have been investigated. The system’s residual life is computed based on residual-life computation algorithms.