Reliability of Polymer Reinforcement and Solder Alloy Material Sets

Anna Lifton, Paul Salerno, Cole Sandvold, Pritha Choudhury, Raghu Raj Rangaraju and Eric Bradley
MacDermid Alpha Electronic Solution
NJ, USA

The utilization of larger Ball Grid Arrays (BGAs), ceramic packages, or Wafer-Level Chip Scale Packages (WLCSP) to increase device functionality requires enhanced reliability in harsh operating environments such as automotive printed circuit board assembly (PCBA). The process of selecting and evaluating polymer reinforcement materials such as underfills and edgebonds has become more demanding and challenging in recent years due to advanced device processing requirements. This complexity arises from a combination of factors including tightening product design requirements, the introduction of novel package materials and technologies, and the adoption of new, innovative semiconductor package designs to meet these processing demands. Each advancement in package technology requires a re-evaluation of the reinforcement material selection process. In order to meet the stringent reliability specifications for thermomechanical, vibration, and drop shock performance of advanced devices, the use of high reliability solders and polymer reinforcement materials such as Edgebond and underfill are becoming more common.

Two primary strategies for reinforcement are: the use of capillary underfill to completely fill any gaps or areas under the device or employing no-flow reinforcement (Edgebond) material to secure only the edges of the device. The choice between these strategies must account for application reliability requirements, device construction, and process throughput.

This paper presents a comprehensive study focusing on new high-performance underfills and Edgebond materials aimed at improving the reliability of various commonly adopted BGAs. The evaluation encompasses observations from various BGAs that exhibit different warpage signatures, pitch and sizes to assess their thermomechanical performance post-reinforcement with either Edgebond or underfill materials. Additionally, drop shock testing is conducted on the assemblies in their as assembled conditions and subsequently after reinforcement with underfill and Edgebond materials.

The findings of this study will shed light on the efficacy of different reinforcement strategies in enhancing the reliability of BGAs under diverse environmental stresses. By providing insights into the performance of new high-performance materials, this research aims to contribute to the advancement of robust electronic packaging solutions, vital for applications demanding high reliability in harsh conditions.

All leading MacDermid Alpha Solder Paste materials and polymer reinforcement materials meet industry requirement regarding electrochemical reliability. In this study we evaluated reinforcement materials influence on mechanical and thermomechanical reliability. Increasing thermal mismatch (ceramic package, bare silicon, mold compound, etc), increasing component size (large BGA, large die, etc.), increasing stiffness of the board (number of layers) and decreasing standoff (small ball size, leadless package) result in increased stress level of the overall system. It becomes in some cases impossible to meet reliability criteria without reinforcing devices. Harsher environmental conditions, exposure to higher temperatures requires applying reinforcement materials with carefully selected mechanical properties suitable for application.