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48 PCB007 MAGAZINE I NOVEMBER 2018 assembly with adhesive significantly exceeded that of the homogeneous assembly without ad- hesive [5] . An edgebond adhesive could be con- sidered to enhance mechanical shock or drop test performance without damaging ATC per- formance, and as a way to enhance the ATC performance of LTS mixed-alloy assemblies and that of other ATC-challenged assemblies. Much additional work is needed in the de- velopment and investigation of LTS alloys. Among other things, the iNEMI team suggests working to better understand the root cause of the interfacial cracking that they observed in ATC, and proposes the utilization of meth- ods in lieu of scanning electron microscopy (SEM) to identify other phases that appear to be present in the alloys. Their team investigating mechanical shock performance hopes to corre- late bismuth mixing and other sol- der-joint morphology, as well as the extent of polymer reinforcement with drop test results. Meanwhile, Wang's team plans to push their ATC tests out further and plans to perform drop tests on mixed-alloy assemblies. Having demonstrated that an appropriate reworkable edgebond adhesive will not damage ATC performance and might even enhance it, Lee and his collaborators would like to investi- gate the use of such an adhesive for enhancing mechanical shock perfor- mance of LTS assemblies. Walwad- kar and colleagues at Intel—having developed and validated a quick- turn test method—look forward to screening large sets of alloys (LTS or otherwise) for fatigue performance. PCB007 References* 1. Richard Coyle et al. "The Effect of Bis- muth, Antimony, or Indium on the Thermal Fatigue of High Reliability Pb-Free Solder Al- loys." 2. Paul Wang et al. "Low Temperature Sol- der Interconnect Reliability and Potential Application in Enterprise Computer and Automotive Electronics." 3. Satyajit Walwadkar et al. "A Novel Approach to Deter- mine Mechanical Fatigue Performance of Solder Material Using Single Joint Test." 4. Raiyo Aspandiar et al. "iNEMI Project on Process De- velopment of BiSn-Based Low Temperature Solder Pastes, Part IV: Comprehensive Mechanical Shock Tests on POP Components Having Mixed BGA BiSn-SAC Solder Joints." 5. Tae-kyu Lee et al. "Low Melting Temperature Inter- connect Thermal Cycling Performance Enhancement Us- ing Elemental Tuning and Edgebond Adhesive." *Editor's Note: All references are from SMTA International 2018 proceedings (October 14–18). Figure 2: BGAs with and without edgebond adhesive.