It depends on the precision you require.
TCs off the shelf vary at least +-2 degrees C. from lot-to-lot.
Personally, I have never soldered a TC in place. I TRIED to do it a couple of times, but it takes too long and typically damages the TC. If I cannot tape it or clamp it securely, then I use a really good thermally conductive epoxy such as Zymet TC201XP.
If I am profiling a scrap CCA to establish an oven profile, I like to use foil tape, like for furnace vents. It only changes the actual temperature about 1 deg. C.
For process control tools, such as for a reflow oven daily or weekly check, or for wave solder or selective solder, I use small metal clamps. All they are is two small strips of metal with two screws clamping them together with the TC weld clamped in between them. The screws go through both pieces of metal into the durostone fixture. The exact temperature being measured is not critical for periodic process control tools; they just have to measure exactly the same every time. So after you create the profile using the taped scrap board, you just run the process control tool through the oven at whatever frequency you determine.
Clamped thermocouples can be replaced easily, and the only variance seen is the variance of the TCs themselves. The clamps pass the heat to the TC without directly exposing them to the solder, so the TCs last a much longer time.
You can never epoxy, solder or tape TCs such that it has very precise repeatability. If you remove a TC that was soldered in place and replace it with another, they are almost never the same.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Robert Kondner
Sent: Tuesday, March 08, 2016 9:54 AM
To: [log in to unmask]
Subject: Re: [TN] Soldering a K Type TCouple to FR4 Board
Hi,
I do not think this is correct.
My recollection of the physics is you can cut the bead off the thermocouple, weld each side to a 3rd material, and get the temperature of the material.
What this does is introduce additional junctions but the final output is always equal to the characteristics of the original bead. Even if you manage to diffuse other materials into the thermocouple wire materials it is the same case.
Anyone else out there have any thoughts?
Bob K.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Bhanu Sood
Sent: Tuesday, March 08, 2016 8:43 AM
To: [log in to unmask]
Subject: Re: [TN] Soldering a K Type TCouple to FR4 Board
Are you sticking the thermocouple head in SAC solder? Be careful!
Once you stick the t/c in SAC solder and melt to 250C (which bwt is above the 185C curie point) the chromel which contains 90-percent nickel and 10-percent chromium and alumel which contains approximately
95 percent nickel, with aluminum, silicon, and manganese making up the other 5 percent will alloy with the tin, changing the temperature e.m.f relationship. You may not have a working thermocouple afterwards.
On Tue, Mar 8, 2016 at 8:14 AM, Bob Wettermann <[log in to unmask]> wrote:
> Morning All:
>
> Has anyone had success in soldering Type K Thermocouples to a PCB. The
> assembly call for a SAC305 no clean alloy....
>
> There are 2 THole connections that will need to be hand-soldered as
> part of this assembly.
>
> Thanks!
>
>
> ______________________________________________________________________
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> Bob Wettermann
> BEST Inc
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> Cell: 847-767-5745
--
Bhanu Sood
Tel: (202) 468-8449
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