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JULY 2019 I SMT007 MAGAZINE 31 My Findings: Which Defect Is More Prevalent? This next section details my own findings at two major companies during my consulting assignments—one at a U.S. medical company and the other at a major Japanese electronics company that supplies to the global automo- tive company (Figures 1 and 2). Recommendations An assignment for you is to look at your own data for some of your higher volume products. Put them in three categories: shorts, opens, and others. Put insufficient, tombston- ing, drawbridge, part movement, etc., into the open category. For the ones that you cannot put into short or open, call them "others." I bet that your findings will be no differ- ent than what I quoted from Orsejo's paper. I am sure of it since I have looked data at many companies over the years. If I'm wrong, I will buy you a drink (nonalcoholic) if we end up meeting at any industry events, such as SMTAI or IPC APEX EXPO. My recommendation is to have six to eight times more shorts than opens, but let me be clear that I am not saying have lots of shorts and opens; I am talk- ing about the ratio of shorts to opens. You always want to work for the total to be on a declining trend, but the total should have more shorts than opens. Why? Shorts will never escape your inspection and test steps, but opens may escape no matter how rigorous your inspection and test regimes are. Opens will be discovered eventually either at a cus- tomer site, or even worse, in the field when it is too late and too expensive to fix. The best part of my recommendation is that it's very easy to achieve. All you need to do to achieve more shorts than opens is to design land patterns and stencils cor- rectly. I may talk about those subjects in future columns. SMT007 References 1. Oresjo, S. "Year 1999 Defect Level and Fault Spectrum Study," SMTAI Proceedings, 2000. 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 implementing 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 has an upcoming SMT class July 22–24, 2019. More details at www.rayprasad.com. To read past columns or contact Prasad, click here. Figure 1: Shorts, opens, and others at a medical company. Figure 2: Shorts, opens, and others at an automotive company.