Attaching thermocuples to a working PCB - Page 1
Forum section: electronics / projects

author: trevwhite
author_rank: Frequent Contributor
timestamp: August 01, 2016, 11:26:16 am
content: I need to attach several thermocouples to a PCB but I can not figure out the best way to attach the thermocouples. Most of the components are surface mount. Any suggestions?Trev

author: sleemanj
author_rank: Super Contributor
timestamp: August 01, 2016, 11:29:01 am
content: Superglue?

author: MosherIV
author_rank: Super Contributor
timestamp: August 01, 2016, 11:30:26 am
content: Epoxy Resign has better thermal coupling.

author: trevwhite
author_rank: Frequent Contributor
timestamp: August 01, 2016, 11:30:58 am
content: Isnt epoxy resin a little permanent though?

author: MosherIV
author_rank: Super Contributor
timestamp: August 01, 2016, 11:35:50 am
content: You never specified that it is suppose to be a temporary arrangement.Assuming the areas where the thermocouples measure will not be shorted out, cover the thermocouple tip with heat transfer compound.Use capton tape to hold the thermocouple wire down, bend the thermocouple so that the tip touches the area you want to measure.

author: trevwhite
author_rank: Frequent Contributor
timestamp: August 01, 2016, 11:38:56 am
content: Yeah I was hoping maybe there was some fancy adhesive out there that holds them in place whilst having good thermal transfer properties and is also easy to remove. Asking for too much?I think the kapton tape and thermal paste is probably the most practical option. Least I can clean everything off afterwards.Thanks

author: trevwhite
author_rank: Frequent Contributor
timestamp: August 01, 2016, 11:41:39 am
content: I just found these...http://uk.farnell.com/labfacility/thermopads-x20/pads-thermocouple-13x18mm-pk20/dp/7218849They look interesting.

author: DTJ
author_rank: Super Contributor
timestamp: August 01, 2016, 11:49:22 am
content: Kapton tape + a dab of heat sink compound is what I use too..

author: Kleinstein
author_rank: Super Contributor
timestamp: August 01, 2016, 01:02:07 pm
content: If the measuring part is isolated one can solder der TC to the board. Even it the solder connection is not good, which often happens with TC, it gives a good thermal contact.

author: Seekonk
author_rank: Super Contributor
timestamp: August 01, 2016, 01:46:24 pm
content: What expected temperatures are we talking about?I sent a board off to UL. When they sent me the board back it was a charred mess. They had epoxied a thermocouple next to a 480V trace. They passed me anyway. UL has a lot of inexperienced people (work study) doing testing. I've talked to them and their dept of understanding is troubling.

author: trevwhite
author_rank: Frequent Contributor
timestamp: August 01, 2016, 01:53:59 pm
content: I am talking under 100C

author: TiN
author_rank: Super Contributor
timestamp: August 01, 2016, 04:12:19 pm
content: Used superglue to fix many little AWG36 Omega thermocouples over the board for thermal evaluation.Works ok, but often need thermocouple repair/welding (as tip easy to break).Alternative is solder Type-T (one of conductors if which is copper) thin TC to component pin/pad, if you have isolated or grounded pads. Beware galvanic connection.

author: PChi
author_rank: Frequent Contributor
timestamp: August 01, 2016, 05:43:21 pm
content: I have tried thermally conductive adhesive but usually the thermocouple just fell off.I have also used double bubble epoxy resin with success. It was usually possible to peel the thermocouple off with the help of a scalpel without damaging it.

author: DutchGert
author_rank: Frequent Contributor
timestamp: August 01, 2016, 06:27:31 pm
content: Tape/glue the wires of the thermocouple somewhere on the pcb or enclosure as a strain relief. Then, bend the tip of the thermocouple in a way that it pushes itself against the object to measure. Then just glue the tip in place with a small drop of superglue.This works for me with lots of thermocouples attached to a single board. It sticks enough to safely handle the product, it gives good results and with a bit of force u can salvage the thermocouples afterwards (~1 in 10 dies in the process)

author: nfmax
author_rank: Super Contributor
timestamp: August 01, 2016, 08:34:56 pm
content: Labfacilty have a range of thermocouples with various mountings you might look at, including patch, bolt, washer, and magnetic mounts:https://www.labfacility.com/temperature-sensors/thermocouples-iec/fabricated-and-specialist-thermocouples.html. If you are measuring temperatures regularly, averyuseful supplier!

author: ConKbot
author_rank: Super Contributor
timestamp: August 02, 2016, 01:49:47 am
content: 5 minute epoxy of most varieties on a pcb can be considered temporary for most purposes. It's heat resistance is abysmal, so hit it with a heat gun and it softens up more than enough to scrape if off.