Spherical Bend Test Failure Criteria Correlation in Compliant Systems
Authors: John McMahon, Brian Standing and Meisam Salahi Company: Celestica Inc. and Ryerson University Date Published: 9/28/2014
Abstract: The incidence of Pad Crater damage in Pb-free assemblies continues to be a concern for many manufacturers and end users of electronic assemblies. Some package designers now routinely include non functional pins at the corners of fine pitch area array components. There are various other mitigation techniques in common use depending on the industry sector. Several Telecom sector companies now routinely include some level of mechanical material or application characterization in their ongoing process verification and package introduction procedures. This activity is required because qualification or characterization data is not available. The characterizations that have been completed are specific to package type or design, board resin system and usually even board thickness. In an effort to generate more data an investigative team from the High Density Packaging Users Group (HDPUG) is working to rank many materials by performance using a commonly available over molded ball grid array (BGA) package and a cost effective board thickness. These design parameters were required due to the large number of laminate resin systems in the study. However, the geometry and compliance of these sample assemblies will be quite different from the material combinations that are commonly problematic in actual manufacturing and service life conditions. This paper describes a test program designed to investigate the correlation between these new sample geometries and existing data generated with the investigator’s established test methodology and product representative material sets. Additionally we will examine the correlations between our existing test methods and those employed by HDPUG. The study includes one widely implemented filled epoxy resin system and two other common mid and low loss materials for which test data already exists. The intent is to highlight and separate differences driven by material sets and those induced by test methodology.
Pad Crater, Fracture Mechanics, Spherical Bend Test, Mechanical Test methods