Are insulation pads without fiberglass reinforcement prone to fail?

[Miyuki]

Hi, I want to ask about your experience
Are thin high thermally conductive pads without fiberglass reinforcement prone to failure due to some damage during assembly?
Or is there no reason to worry?

[TimNJ]

Depends whether or not you have Edward Scissorhands doing the assembly.

What are you insulating? TO-220 or similar?

[Miyuki]

TO-220 and TO-247
Both tend to have pretty sharp edges

[bdunham7]

If you are referring to those thin "low-pressure" sil-pads, no I haven't seen issues.  I also don't go overboard trying to squish them out, but they are designed to work over a pretty wide range of clamping forces.

[TimNJ]

With the amount of torque you can put on an M3/M4 screw with normal screwdriver, I don't think you'll run into any issues. If using pneumatic or battery powered screwdriver, you can use some torque limiting to make sure they don't get crushed.

[Siwastaja]

For functional insulation they are fine when carefully assembled. For example in current limited extra low voltage systems where short circuit only causes outage, not shock hazard or fire.

If you need safety against mains voltages for example, they are too risky.

[bjbb]

For functional insulation they are fine when carefully assembled. For example in current limited extra low voltage systems where short circuit only causes outage, not shock hazard or fire.

If you need safety against mains voltages for example, they are too risky.

I have no idea what you are talking about. Any empirical test or reliability data to support this statement?

Have worked at several employers where we used stuff from Bergquist and others that were NRTL-certified where Basic Insulation was required per IEC60950-x and iEC62368-x and IEC61010-1for protection from shock. Passed all Type Tests, factory recurring tests, HALT, and Mil Std 810 environmental stuff.

I am not aware of a single failure of these thermally-conductive insulators during last 25 years. We used these things right up to their rated temperature and rated voltage. If you use non-certificated garbage, or you design widgets that use components outside of their rated range, or if your production process sucks, then they will fail and your product will suck and the engineers will be (rightfully) out of work.

If you want to be an engineer, you must be able to understand and numerically quantify 'risk'. 

[bdunham7]

Have worked at several employers where we used stuff from Bergquist and others that were NRTL-certified where Basic Insulation was required per IEC60950-x and iEC62368-x and IEC61010-1for protection from shock. Passed all Type Tests, factory recurring tests, HALT, and Mil Std 810 environmental stuff.

If you are referring to these or similar:

https://www.mouser.com/datasheet/2/48/ERGQUIST_SIL_PAD_TSP_1600S_EN-1534462.pdf

than do note that those are the fiberglass reinforced ones and the OP was specifically asking about ones without fiberglass.  I'm not sure why they want that, cost or some other reason, but I'd sure want to know the specific product before I declared them 'safe' for mains voltage.

[Miyuki]

I'm considering the use of SARCON® UR or YR, or another alternative
They have the same voltage rating as reinforced ones, just are much squishier and tend to have a better thermal conductivity

[T3sl4co1l]

I've certainly seen some TIMs that are very soft and tend to squidge out, particularly on repeated use -- troubling for a prototype, but still fine in production.  That includes some that incorporate fiberglass; I forget what material I'm thinking of, it might've been a Gap Pad(R), a gray one with just enough fiberglass to retain shape but it can crush down quite far if forced -- and it doesn't take much torque on a screw, with repeated application and the uneven pressure of TO-220s.

Note that, even if a TO-220 is biting in quite deeply, there can still be some fibers' thickness left, keeping them apart, and certainly not offering the full dielectric rating of virgin material, but probably still enough for functional purposes.  And that can be fine for flat and smooth surfaces, but any minuscule protrusion, burr, etc. on either surface, and it's hard shorted.  Which again in a prototyping context, you may have just errant metal filings floating around for example (even if doing cutting carefully, well away from the electronics; some can still get tracked in), that's not great.  In production, that can be more carefully controlled, and it may also be hi-potted to confirm.

Note that the difference between functional and any kind of safety, is where the heatsink is grounded.  If internal (insulated/shielded from outside contact; may be floating, or tied to local circuit ground), functional.  If earthed, basic.  If exposed to touch (and isolated, an SELV contact), reinforced.

Ed: as another, not really a case study, these are anecdotal, let's be fair -- I currently have some of this,
https://www.digikey.com/en/products/detail/bergquist/GPVOUS-0-020-01-0816/529937?s=N4IgTCBcDaIEYFMBOZUFoB2ATEBdAvkA
which does a fine job in combination with even clamping pressure -- max clips like
https://www.mouser.com/ProductDetail/Aavid/MAX07NG?qs=%2Fha2pyFaduh3yz0bZfkSwKC%2F0csqKGJb%2FybLWvTVikPdiOobqWHfEw%3D%3D
are excellent.

Tim

[David Hess]

I suspect the idea is that the fiberglass reinforcement allows for a thicker pad made up of a more elastic material for greater compliance without being too fragile.  The pads without reinforcement are thinner and harder which requires better surface finish and flatness.

[Siwastaja]

I have no idea what you are talking about. Any empirical test or reliability data to support this statement?

Get off your high horse and RTFD - read the datasheet.

Some products are rated and qualified for more than functional insulation, i.e., to certain safety standards. It appears this is what you have seen used.

Others do not. They are used to mount CPU coolers, for example. They are very soft and/or brittle and come with significantly better thermal conductivity, up to some 20W/mK. It's easy to pierce such pad especially when thin so that the pad material "escapes" completely.

If you have never heard of this, well, now you did. So look at the datasheets, and when safety matters and you have to pass regulations, use parts specified for such use instead of relying on your feelings of not seeing a failed part - because you have not seen everything.

[Siwastaja]

than do note that those are the fiberglass reinforced ones and the OP was specifically asking about ones without fiberglass.  I'm not sure why they want that, cost or some other reason

Better thermal conductivity. By removing the requirement of certified insulation, you open up the door for significant improvements in performance. Which boils down to the question, what are the voltages involved? If this is for cooling a CPU, then such modern non-fiberglass reinforced is likely the right choice, which is exactly what they are designed for.

[digsys]

eeeep. just saw this thread :-) gunfight at OK corral :-)
Anyway, sent you details of RW tests, and looking at the specs (that product version wasn't around when I did my destructive / comparative tests), it seems quite good.
Worried about the "sharp edges" comment though !! Of the many 10's 1,000s I've used over the years, never had any sharp enough to cut "into" the pad ,, Is it from a reputable supplier? Counterfeit? If you find it is "real'", then it WILL reduce electrical safety (ie distance), and possibly thermal pad efficiency. If it is unavoidable, and not serious high quantities, give them a quick buff on a flat surface with fine abrasive. An option.