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Soldering temperature indicator

flippineck

Sep 8, 2013
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On my fishtank, I have a thin plastic strip on the glass that changes colour in response to temperature. I wondered if there is something similar to assist with soldering?

Thinking of soldering SMT IC's with a hot air gun. Just something additional, for comfort, to confirm once you've melted the solder properly, especially if you can't easily see the connections directly e.g. BGA's, WSON chips etc.

& to help you decide when enough heat has been applied, and more would just be needlessly cooking the component..

I'm visualising say, a white dot sticker that turns into a red dot soon as a suitable temperature is reached. Maybe there's something out there? I've not been able to google anything up so far :(
 

dave9

Mar 5, 2017
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Only thing that occurs to me is pointing an IR temp gun at it for measurement, plus trial and error of surface temp vs underneath solder temp difference.
 

flippineck

Sep 8, 2013
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Good idea, looked at a few on Ebay, one thing I'm unclear on is whether it's possible to get a constantly changing reading from them or whether you get a discrete reading per trigger pull. Or, if they all differ in this respect. I've visions of one set up in a lab stand with it's trigger held down with tape? otherwise it would be assistant standing by and pulling the trigger very quickly many times in succession..
 

dave9

Mar 5, 2017
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I'd wonder if the laser will burn out if you keep it held down, so might maybe make a foot trigger switch so once aimed, you don't need another hand to operate it intermittently.
 

crutschow

May 7, 2021
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I'd wonder if the laser will burn out if you keep it held down
What laser?
The IR temp gun uses a passive IR detector to determine the temperature from the radiated IR energy.
 

dave9

Mar 5, 2017
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^ Yes, I'd think a laser would be necessary unless a very fancy one with a thermal gradients screen to see the component outlines.
 

flippineck

Sep 8, 2013
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Middle of the SMT IC, wherever it's going to be most sensitive to heat damage. Probably right in the centre?

Have ordered a "Max Measure IT-01" IR thermometer gun to try it out. It claims a 500msec response time. No specific mention whether it supports continuous monitoring, none of the Ebay offerings seem to.

The tinkerer in me is having visions of replacing the trigger with a relay fed with a 0.6s on, 0.4s off square wave to at least get a hands-free temperature update every second.

I also found a "Thermax Thermochromic Irreversible (sticky) Label" which goes from 204'C to 260'C in 8 steps. I figure maybe, I could try cutting out a bit of the 250'C panel in it & sticking it on top of the chip. Then when it turns from white to black I know to stop blowing the hot air..
 

flippineck

Sep 8, 2013
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Thermal imaging camera probably a good idea in the light of trials I just tried. I bought a type-k thermocouple for my multimeter, and an IR laser gun thermometer. Fired up soldering iron (small antex one) and looked at the tip temperature with both.

The thermocouple was perfect for measuring spot temperatures, which varied markedly all over the bit (and in to me, unexpected ways).

The cheap IR gun seems to 'average' quite a wide region around the laser target dot. It does update continuously though, although I think it's only good for checking the overall temperature of maybe an inch wide patch, and easily misses small hotspots. This is where it'd be good to try a thermal imaging camera but they are quite pricey for the basic hobbyist.

Bare element region of iron: IR thinks maybe 250'C, thermocouple 300'C
Body of bit around the iron's element.. IR thinks maybe 150'C, thermocouple 280'C
Very tip of iron.. IR thinks maybe 150'C, thermocouple 320'C, right where you put the solder

The thermocouple seems to indicate there's a kind of heat energy concentrating effect as the tip thins out to a point, the very tip (furthest part of the bit away from the element) is the hottest part in terms of specific temperature!

Thermocouple maybe hard to integrate into the soldering process though. Saving my thermax label for when I finish practicing SMT soldering & try operating on a board worth money.
 
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