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Voiding in the Thermal Ground Pad of BTC Components

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    Phil Zarrow: With the advent of bottom terminating components, one of the nemesis of the electronic assembler is voiding in the thermal ground pad of the BTC component.

    Derrick Herron: Absolutely. Voiding can lead to hot spots in the component, which will eventually lead to a shortened life span, because the component will basically burn out. Not having those voids in there will allow better heat transfer from the component down into the board and away from the component.

    Phil Zarrow: What are some of the approaches that Indium has taken toward mitigating this problem?

    Derrick Herron: Yes. In the past, we’ve tried things with using a thin, flat, custom-shaped preform for the pad itself. The only problem with that is that you need the custom preform. You need the special tooling to make that part in that shape. Now, what we’ve tried is using Solder Fortification® Preforms, which can come packaged on tape & reel, ready to use. I’ve actually got some right here. They’re ready to go and can be fully automated in the process.

    Phil Zarrow: What would be the proper approach toward replacing these preforms?

    Derrick Herron: The pick-and-place machine will see them just like a component. Standard components come as 0402s, 0201s, and these preforms come in those same sizes, so it’s very easy for current equipment to just pick them up and place them. In the assembly, they will go right into the solder joint on that thermal pad.

    Phil Zarrow: What are some of the differences you’ve seen in using the Solder Fortification® Preforms?

    Derrick Herron: Well, with experiments, we haven’t directly to the flat, thin performs that have been used in the past. The basic idea is that these will be more readily available, more easy to put into current production. What we have seen is that voiding is not only decreased, but the distribution of percentage of voiding from one component to another on the same board or on various boards, you actually decrease that distribution. We’ve tried using one 0201 preform, two 0201s, and one or two 0402s, and we’ve actually seen the 0402s give slightly better results that the 0201s. And when using two 0402s, you can actually get down to, fairly consistent around, 12 percent voiding in the solder joint.

    Phil Zarrow: What would be the proper approach toward replacing these preforms?

    Derrick Herron: Like I say, these are going to be used with paste, so you’re going to print your pastes just like you always would. And then this preform is going to be put into the paste on that thermal pad. So, what happens is when the component comes down, it’s actually going to be held at an angle. The preform is going to be thicker than that paste deposit. You have a large surface area of paste, which is able to outgas. But you have a preform which melts during the reflow process and that allows that component to come down. It’s also adding more metal volume into the solder joint, as well. And, like I say, we saw that using two 0402s worked the best, so there has to be some mechanism there with more solder volume itself helping with decreasing the voiding.

    Phil Zarrow: You’ve done testing using the Indium10.1 low-voiding solder paste. What are some of the results you’ve seen?

    Derrick Herron: In the experiments that we did, we used our Indium10.1 Solder Paste, which was designed specifically with QFN voiding. It was designed to have the lowest amount of voiding of any of our solder pastes at the time. So, using that, we started out with already low voiding percentages, between 15 and 20 percent, and then we were able to decrease the voiding even farther, using these preforms in conjunction with that paste.

    Phil Zarrow: I see, Derrick, that the Solder Fortification® Preforms have a myriad of advantages. Where at Indium Corporation can I find out more information about these?

    Derrick Herron: Well, we can be reached directly at our website, www.indium.com, or I can be contacted directly through my email at dherron@indium.com, as well.

    Phil Zarrow: Great. Derrick, thank you very much.

    Derrick Herron: Thank you.