Effect of compression loads on the solder joint reliability of flip chip BGA packages

Rising power dissipation requirements in modern semiconductor devices have created a need for high performance thermal solutions. These thermal solutions require increasing amounts of compression loading to ensure good conductance of thermal interface materials and retention of massive heat sinks in shock conditions. The impact of these loads on the reliability of the package solder joints has typically not been considered in both finite-element-based and statistical-based assessment methodologies for fatigue of solder joints. The goal of this work is to provide an understanding of the effects of these loads and provide new methods to characterize the limits of these loads for reliable operation throughout the life of the component. This paper discusses the critical impact of the thermal compression loads on solder joint reliability for both fatigue and creep. In this work, a new experimental test method is described. This method utilizes a fixture that simulates the thermal solution load during life testing. The fixture design allows the load and support conditions to be varied and their effects studied. Testing of surface mounted components has been conducted and implications to the standard statistical life prediction methods are discussed. In addition, finite-element-based modeling assessments for the loading conditions have been performed. The analysis shows the impact of the thermal compression load on discrete solder joints for both thermal cycling and long duration high temperature (bake) testing. The implications of compression loading to analytical and statistical life prediction methods are discussed. Based on the experimental and modeling data, load and support boundary condition limits are proposed as the best way to prevent solder joint failures.