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102 SMT Magazine • June 2016 by Stephen Las Marias I-CONNECT007 Knoll Evangelista is the director of the EMS Components and Group Operations of Laguna, Philippines-based electronics manufacturing services firm EMS Components Assembly Inc. With more than 25 years in the electronics as- sembly industry, Evangelista has seen the evo- lution of the soldering process—from adhesive component mounting with the solder wave ma- chines to screen printing with reflow ovens. He had also set up over 35 SMT lines for high vol- ume production of products ranging from stor- age devices, consumer electronics, automotive electronics, and medical devices. In an interview with SMT Magazine, Evange- lista speaks about the solder paste printing chal- lenge, what factors impact the process, and best practices to consider. Stephen Las Marias: From your perspective, what are the biggest challenges when it comes to solder paste printing? Knoll Evangelista: Reliability of solder joints in electronic products is the biggest challenge, and it depends on the following factors: stencil printing and quality of reflow soldering. Las Marias: How does the solder paste material impact the process? Evangelista: The size of the solder paste gran- ules has an impact on the process as it depends on components to be mounted. The pitch dis- tance of ICs, the ball array size, and the distance of BGAs have to be considered in selecting the solder paste material. Las Marias: How do the tighter tolerances and even narrower PCB lines and spacing affect the sol- der paste printing process? Evangelista: More than 50% of defects in assem- bly of printed circuit boards are attributed to the solder paste printing process. The volume of paste deposit during screen printing is a big factor im- pacting the quality of solder joints. It requires de- sign of experiments (DOE) to get the right param- eters of screen printing machine. It also involves optical inspection to measure the volume of paste deposit to assure consistency of paste application. The surface mount components such as chip scale packages (CSP), fine pitch BGAs are the challenges in stencil printing and reflow profiling capabili- ties. Due to tighter tolerances, 3D X-ray inspec- tion is required, which offers capabilities beyond those of microscopes and naked eye. The Reliability Factor in Solder Paste Printing FEATURE INTERVIEW

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