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Oven Profile:Thermal Couples Letting Go

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Oven Profile:Thermal Couples Letting Go | 3 February, 2012

We've been having issues with our current process of oven profiles. We use a high temp adhesive to bond the thermal couples to the desired components. The issue of them letting go or releasing during reflow temps are hit or miss. Majority of our buisness consists of Pb free profiles. My idea is to use an alloy with a higher melting range and solder the thermal couple onto the component of interest .. say... Sn10/Pb90 which has a melting range of 268-302C. Has anyone tried this method? Any obvious risks involved? We use a 10 zone BTU Pyramax125 with the max reflow temp of 270 traveling at 38ipm.

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Oven Profile:Thermal Couples Letting Go | 4 February, 2012

You bet. Using a high temperature solder is a perfectly reasonable way the attach thermocouples. Just remember that the solder will not flow on the thermocouple. You need to use a solder iron to lay the solder over thermocouple to hold it in place.

For a given thermal oven recipe, expect that the temperature of a solder connection to be higher than the temperature of a component body.

Going backwards, the a possible reason that you've had spotty results attaching your thermocouple to components is that some components have mold release on them, which would make them very slippery. Additionally, those components are less likely to take conformal coating, but that's another story.

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