SMT Magazine

SMT-Oct2017

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8 SMT Magazine • October 2017 by Stephen Las Marias I-CONNECT007 Creating the Perfect Solder Joint What are the characteristics of a good sol- der joint? Generally, from a visual standpoint, they should be smooth, bright, shiny, clean, and have a nice concave solder fillet. At least, these characteristics describe solder joints for through-hole components. What about for surface-mount devices? Or bottom terminat- ed components? Moreover, how do you en- sure that inside those joints, good intermetallic bonds are formed? Since all solder joints aren't created equal, the first step is to understand what is expected or required of that joint, according to Rick Short of Indium Corp., during my interview with him at the recent NEPCON South China trade exhi- bition in Shenzhen, China. Solder joints play several different roles, and they represent several different opportuni- ties to be a problem, a partial improvement, or a complete improvement. For example, there are solder joints that are necessary for phys- ical strengths, such as holding components, like connectors. We often wiggle and yank our phone jacks—there's a little bit of solder trying to hold all that together, and we keep doing it over the course of ownership of the device. So, those joints must be very robust with regard to physical strength. Other solder joints are mere- ly there to conduct electricity. They don't have much of a harsh life at all, and it is a relative- ly easy life for them. Other solder joints, mean- while, are involved in very high heat dissipa- tion demands. They must conduct electricity and heat, and they might also need to address physical strength issues. So, many different op- portunities exist for solder joints to either cause you problems or contribute to the success of your finished goods. Nobody, including myself, wants field fail- ure. I often travel overseas for work, so I defi- nitely don't want the airplane I'm on to experi- ence that "field failure." But going back to our topic on solder joints, I vividly recall that fa- tal plane crash a few years ago that was main- E DITOR'S NOTE

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