Issue link: https://iconnect007.uberflip.com/i/1305670
84 SMT007 MAGAZINE I NOVEMBER 2020 • How do you ensure you get sufficient paste thickness to prevent potential opens without getting too many voids? • How do you prevent paste dripping into via holes in thermal pads? • What do you see as the major concerns in PBGA, and how do they compare to PQFP? • What is their experience with head-in-pil- low (HIP)? • If you are doing all you can about paste height, reflow profile, do you think the component supplier is responsible for HIP? • Do you prefer copper-defined pad or sol- der mask-defined pad, and if so, why? • What do you think of the approach used by some companies where solder mask is sprayed up to the edge of the pad with zero clearance? • Do you prefer via in pad or tear-drop design, and if so, why? • Did you conduct any evaluation on PCB routing for different pitch, pad sizes, line width/space, etc., and their impact on layer count? • Did you experiment with different pad sizes and their impact on process yield? Conclusion The idea behind the questions in this column is to establish whether the company has done extensive process evaluation and whether they understand the importance of critical materi- als and process variables on product quality and reliability. It will be obvious within a very short time during the visit if there is someone in the company who understands these issues or if they are just following the recommenda- tions of component and material suppliers. How many component or material suppliers do you know who build PCBAs? How useful would their recommendations be? I should also note that the intent of these questions is not to dictate the process to the company but to assess their understanding and capability. You should focus mainly on the end requirements. Let the assembler worry about how best to meet those requirements. You are simply trying to establish whether they can meet your requirements. In my next column, I will conclude this series with questions on quality and RoHS compli- ance. SMT007 Ray Prasad is the president of Ray Prasad Consultancy Group and author of the textbook Surface Mount Technology: Principles and Practice. Prasad is also an inductee to the IPC Hall of Fame—the highest honor in the electronics industry—and has decades of experience in all areas of SMT, including his leadership roles imple- menting SMT at Boeing and Intel; helping OEM and EMS clients across the globe set up strong, internal, self-sustaining SMT infrastructure; and teaching on-site, in-depth SMT classes. He can be reached at smtsolver@rayprasasd.com and regularly offers in-depth SMT classes. Details about classes can be found at rayprasad.com. To read past columns or contact Prasad, click here.