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Technical Editor Pete Starkey presents his list of the top 10 SMT Tech Tuesday articles for 2014. The year's topics cover a wide range and include printed electronics, lead-free processes, preventing tin whiskers, stencil printing challenges, and thermal management issues.
At #10, Nanocopper-based Solder-free Electronic Assembly Material, by A. A. Zinn, R. M. Stoltenberg, J. Beddow, and J. Chang, Lockheed Martin: In response to government legislation and regulation around the world regarding lead content in consumer electronics, electronics producers have quickly converted to lead-free tin/silver/copper (SAC) solder. This paper from experts at Lockheed Martin outlines the development of a novel nanocopper material--from synthesis to board level integration--as a solder-free electronic assembly material.
At #9, Meeting Future Stencil Printing Challenges with Ultrafine Powder Solder Pastes, by Edward Briggs, Indium Corporation: Solder pastes comprised of finer particle solder powders may help with stencil printing, but increased surface oxide associated with finer powders may also reduce the reflow process window. This paper provides a comparison of the transfer efficiency of different solder powder particle sizes and visually observes post-reflow results in both optimal and harsh conditions.
At #8, Head-in-pillow X-ray Inspection, by A. Castellanos, Dr. Z. Feng, D. Geiger, and M. Kurwa, Flextronics International Inc.: Identifying product defects associated with the manufacturing process is a critical part of electronics manufacturing. In this project, the authors focus on how to use AXI to identify BGA head-in-pillow (HIP), which is challenging for AXI testing. The goal is to understand the capabilities of current AXI machines.
At #7, Influence of Microstructure on Mechanical Behavior of Bismuth Pb-free Solders, by David B. Witkin, The Aerospace Corporation: Certain alloys that contain bismuth have shown superior reliability in PCB testing, but they have not been widely used in electronics manufacturing due to their Bi content. This article focuses on the microstructure and behaviour of Bi-containing alloys, and compares this data with that of SAC305.
At #6, Conformal Coating Over No-clean Flux, by Karl Seelig and Timothy O’Neill, AIM: As the proliferation of modern-day electronics continues to drive miniaturization and functionality, electronic designers and assemblers face the issue of environmental exposure and uncommon applications never previously contemplated.
At #5, Testing Intermetallic Fragility on ENIG Upon Addition of Limitless Cu, by Martin K. Anselm, Ph.D. and Brian Roggeman, Universal Instruments Corporation: Authors Dr. Martin Anselm and Brian Roggeman present data concerning the intermetallic strengths and failure modes of two bond pull test methods. Specifically hot bump pull (HBP) and cold bump pull (CBP) testing are compared where Cu is added by the copper pins of the HBP tester or by Cu power in a second reflow followed by CBP testing.
At #4, Grain Refinement for Improved Lead-free Solder Joint Reliability, by K. Sweatman and T. Nishimura, Nihon Superior Co., Ltd and S. D. McDonald, M. Whitewick, and K. Nogita, University of Queensland: While grain boundaries can themselves contribute to failure, the reduction in the anisotropy of a solder joint by increasing the number of randomly oriented grains would be an advantage and the observation has been made that joints with a finer effective grain size last longer in thermal cycling than otherwise expected.