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Problems with Reflow Oven ProfilesBoard Talk
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TranscriptPhil Jim Phil "I use at least three TC's on every board and more on complex ones." So far so good. "I've heard you guys talking about attaching TC's with epoxy or a high-temp solder. Well, I use Kapton tape and I get good results." Jim Do you have webcams in your reflow section? Kapton is a great material, that's not the problem. The problem is the adhesives. The adhesive that holds that Kapton layer on are temperature sensitive. They soften at high temperature and when it softens, contact between the thermal couple and what you're trying to measure can be reduced and it doesn't take much to give you an inaccurate reading. Remember, the greatest risk is when the temperature's the highest. That's at peak reflow temperature, and that's probably the most critical point, particularly if you're doing lead-free and you're working with a really tight process window. What's confusing is as you go through cooling, the adhesive re-hardens and it looks fine when it comes out. So the bottom line is, the Kapton tape works most of the time, but you can never be sure on any given profile on any given thermal couple. So what should you do, Phil? Phil And unless you want to be doing this over and over and over again. You want to do this right. Use some solder wick. Get as much of that old solder off and then you want to use a very small amount of solder, high temp solder or a conductive epoxy. The reason we emphasize using a small amount is you don't want to have too big a mass at that interconnection that may give you wrong readings, inaccurate readings. You do that and you know what? You know all that Kapton tape you bought, use it for strain relief. So again, this is the most time-tested method, either high-temp solder or the conductive epoxy. As Jim said, we've tried everything. Did I ever tell you about the time I tried using RTV? It was one of those things that seemed like a good idea at the time, but well, we won't go there. Okay, we are Phil Zarrow and Jim Hall, the Assembly Brothers, and we bid you good day. And remember ... Jim Phil Jim |
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