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Thermocouple attachment on fine pitch component.



Thermocouple attachment on fine pitch component. | 11 April, 2001


I found it's hard to attach thermocouple on profile board at fine pitch component by high temp solder. Does any one know the good way to do it?

Thanks in advance. Dave

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Thermocouple attachment on fine pitch component. | 11 April, 2001

High temp solder is the best, but your profiler manufacturer will have some type of adhesive.

I know KIC does.

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Thermocouple attachment on fine pitch component. | 11 April, 2001

No, there's not a really great epoxy product for attaching thermocouples in reflow.

Specifically, what's your problem?

From Sanders Temprobe verbage ...


There are two general classes of material commonly used to adhesive bond thermocouples. One is accelerator or UV activated adhesives that set in seconds, but are only rated for around 120�C. They do not hold up well in reflow, and are more commonly used for wave solder applications. Special high temperature, two part epoxies are rated up to 260�C, but require several hours at elevated temperature to cure. A thermocouple is properly installed with a small amount of adhesive.

PRO: * These products are easier to use than high temperature solder. * The accelerator and UV activated products set quickly, to speed installation. * High temperature, two part epoxies will withstand reflow temperatures for many cycles. * Both products can attach thermocouples to unsolderable surfaces such as plastic or ceramic components or FR4 board.

CON: (Accelerator or UV activated adhesives) * Their low temperature rating makes them prone to popping off during reflow, where peak temperatures are around 210�C. * Their relatively poor thermal conduction makes it essential that the thermocouple junction be held securely against the surface to be measured while the adhesive is activated. * They are usually easy to remove by "popping " them off with a knife. However, they do leave a film-like residue that is noticeable on FR4 and dark components, and can be difficult to remove. The most effective solvents, like acetone, also dissolve plastics, and can therefore damage circuit boards.

CON: (Epoxies) * High temperature epoxy requires an oven cure of several hours. This is inconvenient, especially for quick trouble shooting. It also requires careful fixturing to insure that the thermocouple junction stays in contact with the surface to be measured, throughout the oven cure cycle. * It is difficult to remove this material cleanly, without damaging the board or component. � Quick curing epoxies like "5 minute" epoxy are rated in the range of 130�C, so they often pop off during reflow.

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Michael Parker


Thermocouple attachment on fine pitch component. | 11 April, 2001

I've used Super Glue, with Kapton tape. The glue leaves a small residue and the tape acts as a strain relief.

If you can sacrifice the board, drill a small hole through the board, push the exposed ends of the thermocouple up from the back side, lay the wire flat on the topside surface underneath the part. You put the hole right in the middle of where the fine pitch part is located. This gives a very good measure for profiling.

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Thermocouple attachment on fine pitch component. | 11 April, 2001

More often than not lately, we use Al tape [like Brian W mentioned in a recent thread].

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Terry Burnette


Thermocouple attachment on fine pitch component. | 17 April, 2001

Dave, I use Dexter Hysol epoxy 9340 gray. It's a two part epoxy kit. Thermally conductive and electrically insulative. Cures in about 10 minutes at 100C. Terry

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