THERMALLY INDUCED OUT OF PLANE DEFORMATION ANALYSIS FOR A FLIP CHIP ON FLEX 35MM TBGA

摘要

Over the last several years, higher density flexible substratesrnhave been introduced into high volume electronicsrnassembly. As with any new technology, there are newrnchallenges that arise in processing, reliability testing,rnmaterial selection, and even fixturing. One of the mainrnassembly issues with laminate structures is warpage due tornthe CTE mismatch between the laminated materials. Therngoal of this research was to utilize moiré techniques torninvestigate out of plane deformation of a 35mm TBGArncomponent while in a reflow profile. The moiré analysisrngave the out of plane deformation as a function of time andrntemperature for the test vehicles used throughout thernexperimentation.rnThere are several reasons for PWB or substrate warpage: therninherent CTE mismatches of the substrate building blocks,rnthe transient temperature difference in the laminatedrnsubstrate materials, and the rigidity of the substrate.rnWarpage from all of the above causes could affect flip chiprnattachment yield for first level interconnects. Warpagerncould cause misalignment between the die and the substraternand/or prevent the solder balls from making contact with thernsubstrate flip chip pads during reflow, therefore therndeflection of the substrate at reflow temperatures should bernwell understood for proper reflow process characterization.rnThis out of plane deformation experienced in the reflowrnsoldering process was investigated experimentally andrnstudied via moiré techniques. The output from the moirérnanalysis gave real time flatness measurements of thernsubstrates and aided in the development of a robust reflowrnprocess that resulted in yields of 98% or greater for a widernrange of fluxes.