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94 SMT007 MAGAZINE I JULY 2019 Conclusion Overall, there are several factors that ensure a reliable solder joint: • The selection of the correct tip profile for the tip-to-pad contact area • A power supply system that can provide enough thermal energy to meet the temperature requirements with no overshoot • The ability of the heater/tip to form an efficient energy bridge within a defined time frame • Good-quality solder wire • Operator skill Above all, it is the skill of the operator that becomes the overriding factor, since even the best tools will not perform well in the hands of unskilled or poorly trained personnel. SMT007 References 1. P. Roubaud, G. Ng, G. Henshall, R. Bulwith, R. Herber, S. Prasad, F. Carson, S. Kamath, A. Garcia, "Impact of Intermetallic Growth on the Mechanical Strength of Pb-Free BGA Assemblies," IPC APEX EXPO Techni- cal Proceedings, 2001. 2. T. An, F. Qin, G. Xia, "Analytical Solutions and a Numerical Approach for Diffusion-Induced Stresses in Intermetallic Compound Layers of Solder Joints," Journal of Electronic Packaging 136(1), 011001, March 2014. 3. J. Servin, "Method to Measure Intermetallic Layer Thickness and Its Application to Develop a New Equa- tion to Predict Its Growth," IPC APEX EXPO Technical Proceedings, 2013. 4. D. Hillman, R. Wilcoxon, T. Pear- son, P. McKenna, "Dissolution Rate of Specific Elements in SAC305 Solder," SMTA International Technical Proceedings, 2018. 5. Soldering recommendation by Halo Electronics Inc. USA. *In physics and materials science, the Curie tempera- ture or Curie point is the temperature above which certain materials lose their permanent magnetic properties to be replaced by induced magnetism. The Curie temperature is named after Pierre Curie who showed that magnetism was lost at a critical temperature. For more information, contact Michael Gouldsmith and Zen Lee, co-directors at Thermaltronics USA Inc., Great Neck, New York; Figure 9: Conventional solder tip heater technology. Figure 10: CHT tip/cartridge.

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