Reliability investigation of traditional tin-silver-copper and micro-alloyed solder alloys

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Supervisor:
Dr. Krammer Olivér
Department of Electronics Technology

The thesis summarises the necessary informations of the technology of reflow soldering with its technical parameters and the currently applied mechanical qualifying methods. The two utilized methods in the examination of the structure of the soldered joint’s fractures are optical microscope and scanning electron microscope. Throughout the review of the current literature of the topic above, I was comprehensively examining the mechanical effects of various accelerated life-time tests on soldered joints, as well as the behavior of different doping metals for solder alloys. Two different kinds of solder alloys were applied in my experiments, the SAC305 (Sn3Ag0,5Cu) which is the traditionally used alloy in the industrial practice, and the product of Henkel, called Innolot (Sn3,8Ag0,7Cu3Bi1,5Sb0,2Ni). During the studies, I assembled 0603 SMD resistors on FR4 substrate, particular design of the department soldering was carried out by vapor phase soldering. The soldered joints were aged in two ovens at different, but both elevated temperatures, periodically analyzing the shear strength of the joints and, after accurately preparing the samples, the rate of growth of intermetallic layers and appearance of fracture surfaces in scanning electron microscopes. By the end of the 1500 testing hours, the models appeared as follows: the growth of intermetallic layers was insignificant in both samples at 100 Degree Celsius (app. 3 μm), whilst at 150 Degree Celsius SAC305 alloy showed a growth of 8,4 μm, and Innolot 10,4 μm. Scanning the fracture surfaces, we found a honeycomb-like pattern, specific to ductile fractures. The shear strength of the soldered joints created by Innolot exceeded the potency of SAC305 by 25%. In this experimental comparison of the alloys, based on the results of my tests, I can recommend the application of Innolot in preference of SAC305 in the practice of soldered joints.

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