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Avoid the Void®: High-Temperature Soldering with Semiconductor-Grade Preforms

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  • Avoid the Void

  • Phil Zarrow: Andy, voiding is a major problem in electronic assembly in general, but it really manifests itself in high-temp applications.
     
    Andy C. Mackie, PhD, MSc: Correct. Yeah. Voiding, as always, is an issue of reliability. In SMT it's more sort of a mechanical issue. In these high-temperature applications, you need to be sure that you're getting the heat away from the die, although they can operate at high temperatures, you don't want them essentially getting thermal runaway. You can get to the point where the voiding is so high that the die are essentially thermally insulated from the substrate. The heat really needs to escape from the die, particularly through the bottom of the die.
     
    Phil Zarrow: We're talking a whole other magnitude of void reduction compared to general electronic assembly.
     
    Andy C. Mackie, PhD, MSc: Yeah. In some of these higher power applications we're seeing voiding of just a single figure percent or even a half a percent.
     
    Phil Zarrow: What is Indium Corporation doing with regard to helping customers Avoid the Void®?
     
    Andy C. Mackie, PhD, MSc: Well, we recognized early on that discussions that we were having with our customers were leading us in the area of eliminating the amount of oxide there is on the surface of the preforms, and typically with silicon and germanium. It's very difficult to do with just purely hydrogen in the forming gas. You have to start off with a low oxide in the first place. That means that we actually generated some semiconductor-grade, as we call them, preforms that actually have the oxide chemically reduced so that the final preform in its application produces very low voiding.
     
    Phil Zarrow: That would be one of the key differences between standard-grade preform and semiconductor-grade?
     
    Andy C. Mackie, PhD, MSc: Yeah. Correct. It's certainly more than a marketing term. It's an instance where we've been driven by customer requests to produce a material with a higher quality, maybe a lower oxide. In every instance it means an increased functionality of the material.
     
    Phil Zarrow: Now, Indium Corporation has done some extensive experimenting. Can you discuss some of the data?
     
    Andy C. Mackie, PhD, MSc: Sure. We've looked at a variety of different things, but, again, the primary cause of the voiding that we're seeing at customer sites is oxide. We've tried covering up the oxide with gold—that's plating with gold—it didn't work at all in reducing voiding. Actually chemically reducing the oxides is definitely the way to go, and we've proven that in our work.
     
    Phil Zarrow: And, the discussion of this is in your paper, Die-Attached Voiding Reduction in Gold Alloy Solder Preforms.
     
    Andy C. Mackie, PhD, MSc: Correct.
     
    Phil Zarrow: We can find that on the www.indium.com website. And, for further discussion?
     
    Andy C. Mackie, PhD, MSc: For further discussion, feel free to email me. I'd be very happy to receive emails at amackie@indium.com, as always.
     
    Phil Zarrow: Andy, thank you.
     
    Andy C. Mackie, PhD, MSc: Phil, thank you.