This is an established test, not for reliability, but to determine
whether solder mask or conformal coating will vesicate. It has been in
use for decades and is well established in literature. For ex.,
Tautscher mentions it on p. 10-31 of his book (1976) and cites
MIL-STD-810 method 507 procedure 1:
2 hours at 115°C ±5°C, 15 psi ±5 psi followed by 1 hour at 125°C ±5°C,
25 psi ±5 psi. He calls it the "autoclave test".
In my book (1986), on p. 290, section 26.2, I suggest using a domestic
pressure cooker for 2 - 4 hours and examining it with a 10x magnifier
for signs of vesication. On p. 138, I explain the mechanism of
vesication, with a photo of a circuit on p. 140 (Fig. 13.5) with bad
vesication after a pressure-cooker test.
So, yes, this test has been around for a long time and is very useful to
determine that the adhesion of coatings is good, having been put over
poorly cleaned products. I would say that this test is an absolute must
when applying conformal coatings over "no-clean" flux residues. That
having been said, 72 hours seems somewhat exaggerated, unless you are
seeking potential delamination of inner layers.
Brian
Glynn Shaw wrote:
> Customer is taking fully loaded, tested assemblies and cooking them:
>
> 2 atmospheres, absolute
> 121 deg C
> 100% humidity
> 72 hours
>
>
> Pass-fail criteria: boards must appear cosmetically identical, before and
> after cooking.
>
> They don't... but the circuits aren't falling off the bones and the boards
> still function electrically after drying :-)
>
> Question: is this a valid/known Jedec, IPC, or Telecom test or is customer
> using grandma's recipe? End use is cell phones.
>
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