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October 2017 • SMT Magazine 79 References 1. IPC—Association Connecting Electron- ics Industry, IPC 4556. 2. Milad, G., "Final Finish Specifications Overview IPC Plating Subcommittee 4-14," Sur- face Mount International Proceedings, 2015. 3. Ejiri, Y. Noudou, T., Sakurai, T., Arayama, Y., Tsubomatsu, Y., and Hasegawa, K. "Influence of Surface Finishes and Solder Alloys on Solder Ball Joint Reliability," Surface Mount Interna- tional Proceedings, 2015, SMTA website. 4. Wolverton, M., "Quality, Reliability and Metallurgy of ENEPIG Board Finish and Tin- Lead Solder Joints," Surface Mount Internation- al Proceedings, 2011. 5. Zhao, C., Shen, C., Hai, Z., Basit, M.M, Zhang, J., Bozack, M.J., Evans, J.L., and Suhling, J.C., "Quality, Reliability and Metallurgy of EN- EPIG Board Finish and Tin-Lead Solder Joints," Journal of Surface Mount Technology Articles, 29-2, 4/1/2016, SMTA website. 6. Ghaffarian, R., "Effects of Board Surface Finish on Failure Mechanisms and Reliability of BGAs," Surface Mount International Proceed- ings, 1998, pp. 59~69, SMTA website. 7. International Technology Roadmap for Semiconductors, ITRS website. 8. International Electronics Manufacturing Initiatives, INEMI website. 9. Ghaffarian R., "Update on CGA packag- es for space applications," Microelectronics Re- liability. Jan 15, 2016. 10. Choubey, A., Ghaffarian, R., "FEA and Analysis for BGA/CGA Assemblies under Ther- mal Cycling," Surface Mount International Pro- ceedings, 2016, SMTA website. Reza Ghaffarian is principal engineer with the Jet Propulsion Laboratory. Figure 13: Representative SEM photomicrographs images with EDS elemental analysis of LGA1156 solder conditions after 200 thermal cycles (TC, -55°C/+125°C), (left), 200 TC plus 324 hours aging at 125°C (middle), and a 200 TC plus 100 thermal shock cycles (-65°C/+150°C), right. RELIABILITY OF ENEPIG BY SEQUENTIAL THERMAL CYCLING AND AGING By Duane Benson, Screaming Circuits There are two primary types of causes of board warping: process related at the fab or assembly shop, and layout related issues. Determining the root cause is generally a bit of an iterative process. It's tempting to start right off with your fab or assembly partner, but you The Root Causes & Solutions for Warped PC Boards need some information before giving them a call. You'll need such things as the amount of warpage per inch, board size and thickness. With that, you need to take a good look at your design and con- sider copper pours, component size and compo- nent placement. This article talks about some of the design rules that can contribute to warping.

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