What to do with Zig-Zagging TC Readings?

What’s wrong with this picture?

Profile Lose TC

Well if you have ever used Kapton tape to attach a thermocouple, you have certainly seen your share of profiles like this!

So what, it is a perfectly good profile, right?  Yes, but no.  I had a customer who was using KIC’s Navigation (auto prediction) to help create a better “deep in-spec” profile.  The only problem, they were trying to optimize on a TC reading that was bouncing literally all over their PCB.   Navigator is an awesome tool, but it can only work with what you feed it.  If you feed it garbage, it will give you garbage.  In their case, it was trying to find them a new solution where literally every time the board was run the bouncing TC that was attached (or I should say was not very well attached) with Kapton was giving false readings.    Navigator would give a different solution based on what the TC was reading at that given time.   It is like try to put post-it notes on the ocean.

Solution is very simple, eliminate the TC reading from your graph.  You can easily do this with the profile you just ran.  Look what happens, you go from a far out-of-spec of 126% PWI to a far in-spec of 48% PWI.

Profile Lose TC2

So you saved your hard work this time, but you are after all one thermocouple reading short.  You added that TC to your profile for a reason.  Next go around, do yourself a favor and use a better material for attachment, such a conductive double side aluminum tape, which by the way, a recent study from RIT proves it a superior attachment method aside from sticking to your PCB much better.

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