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Temperature Profiling

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#60656

Temperature Profiling | 10 December, 2009

I'm just getting into temperature profiling our PCB's. We recently bought a new reflow oven. The company purchased a mole before I was hired. This is what I will be using.

What is the preferred way to attach the thermocouples to the PCB locations of interest? I'm not extermely well versed in this process, so location is something I have taken extra caution. My curiosity pertains to chip components (0805's 0603's), soic's, d2paks. I read a little about grease. There has to be a good way other than taping them to a component. To me that introduces some error, any type of air gap between the actual lead or part corrupts the data.

Thanks for the responses.

Craig

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#60657

Temperature Profiling | 10 December, 2009

We like to keep one fully populated SMT golden per product (high volume) with t-couples soldered to it. We have best results using high temp. solder to attach t-couples (most permanent). 1) Remove all production solder from the part you are wanting to attach t-couple to; wick pads. + clean leads. 2) Re-install part using high temp. solder. on all leads. 3) Attach t-couple to a lead using high temp. solder. 4) Tape t-couple wires to form sort of a strain relief so they don't pull from solder joint over time. ***If you don't fully solder part with high temp. solder, it will fall off after a few passes. Prior to each build for that product, we run it through the oven to verify oven is O.K. Keep in mind tolerances of t-couples and your oven when determining what demands changes to your zone settings. In our case, our customer (very strict military!!!) advised temp. tolerances and we try our best to meet them + have to report results. The next best method is pressure sensative, high temp. alum. adhesive tape but you will find it hard to work with on surfaces that are not flat and fairly large.

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#60659

Temperature Profiling | 11 December, 2009

We use SMD glue to fix our thermocouples to the PCB, pretty destructive method (although boards will stil work), but there is nothing worse then making a measurement, waiting for everything to cool down, to then find an bad thermocouple connection when everything get visualised on the PC, then having to hold up the SMD line and start all over again.

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#60660

Temperature Profiling | 11 December, 2009

I use aluminum tape. Attach the thermocouple to the solder joint of a component. Use tape to hold down the wires so your thermocouple doesn't break free.

Go to youtube and search "oven profile". There are some great "how to" videos there to help you.

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#60662

Temperature Profiling | 11 December, 2009

Thanks for all the replies.

I'm wondering how accurate just taping the TC down is. It makes sense to me that soldering would be the ultimate. With a process window, the appropraite tape may be sufficient.

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#60663

Temperature Profiling | 11 December, 2009

Here is a link that has a video of the different methods for attaching them and which is most reliable.

http://www.screencast.com/users/beoleary/folders/7%20Ways%20to%20Profile%20for%20Profitability

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#60698

Temperature Profiling | 18 December, 2009

I measured the diference soldering the TC to the pad and just tape down it, because i had a trouble with accuracy of some TC's. For the TC's I just taped down, I used additional heat-conductive paste to make a a termal connection from the TC to the solder joint. I detectet a difference of approximately two degrees. I'm not sure how reliable these results are, because I measured with two different instuments, both with a accuracy of +/-1 degree. But I think the difference will be in this range.

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#60705

Temperature Profiling | 18 December, 2009

I would place the TC under the heaviest component if you can - has the most thermal mass and hardest to get to temperature.

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#60721

Temperature Profiling | 23 December, 2009

In a former life, we used hi temp solder. I've heard of adhesive and taping methods, we just never used them. We too had a "golden" assembly that we would use for routine profiling. Our requirement was to attach a TC to the lowest thermal mass, highest thermal mass, most temperature sensitive component, and on the center of the board. Extra TC's could be used for additional components.

Each method of attachment has it's own inherent issues. Tape can come loose or have air gaps, adhesives may not have the same heat transfer rates, too much hi temp solder can also have heat transfer issues (especially if the glob is too big). Soldering is relatively quick and easy, adhesive requires curing, and tape may not be adhered well. If you have a way to check out all 3 off line, you can determine what works best for you.

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#60736

Temperature Profiling | 26 December, 2009

The negative side to tape is that you could have a small airbubble next to the T/C which will result in an inaccurate reding as the air will be hotter than the joint.

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#60740

Temperature Profiling | 28 December, 2009

I just read an articale that said using metal tape was better then high temp solder.

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kpm

#60745

Temperature Profiling | 29 December, 2009

Why don't you post the link to the article so we can all read the evidence of this.

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