ICSR (Soldering and Reliability) Conference Proceedings


Meeting Future Stencil Printing Challenges with Ultrafine Powder Solder Pastes

Author: Edward Briggs
Company: Indium Corporation
Date Published: 5/13/2014   Conference: ICSR (Soldering and Reliability)


Abstract: The explosive growth of personal electronic devices, such as mobile phones, tablets, and personal music devices, has driven the need for smaller and smaller active and passive electrical components. Not long ago, 0201 passives were seen as the ultimate in miniaturization, but now we have 01005 passives with rumors of even smaller sizes not far behind. For active components, array packages with 0.4mm pitch are virtually a requirement for enabling the many features in modern portable electronic devices. To meet the challenge of stencil printing smaller stencil apertures, there is an increased interest in using finer particle-sized solder pastes to improve transfer efficiency. The smaller particle size results in a large surface area-to-volume ratio that challenges the solder paste’s flux to effectively perform its fluxing and oxidation protection action. The potential resulting surface oxidation can lead to voiding, graping, head-in-pillow, and other defects.

The combination of higher lead-free process temperatures, smaller print deposits, and temperature restraints on electrical components has created several challenges. Two in particular are obtaining consistent volume in the printed solder paste deposit and minimizing the oxidation of the solder powder in the small deposit during reflow. Solder pastes comprised of finer particle solder powders may help with stencil printing, but the increased surface oxide associated with finer powders may also reduce the reflow process window. The focus of this paper is to provide a statistical comparison of the transfer efficiency of different solder powder particle sizes, specifically types 3, 4, 5, and 6, and to visually observe post reflow results in both optimal and harsh conditions.



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