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September 2002

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Subject:
From:
Brian Ellis <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Thu, 5 Sep 2002 09:39:21 +0300
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Bev

Ethylene glycol, as a monomer, its dimer and trimer should not be
confused with polyethylene glycols (PEGs). The latter (Carbowax), with
MWs over about 300 and especially over 1000, will bond terribly with
epoxies at soldering temperatures, causing distinct SIR losses.

You don't say whether the EG has been subjected to high temperatures or
is a room-temperature contaminant. If the latter and it is pure (or a
pure water/EG mix), I would say a simple but thorough DI water wash and
rinse will be sufficient. If it is not pure, (e.g. the stabilisers in
anti-freeze, which may be amines) look to the other contaminants, as
well. If the assembly has passed the Tg of the epoxy since
contamination, the "searching" qualities of the EG may mean some
penetration and a long hot soak may be needed to leach out the absorbed
product.

I would not add anything to the water. EG itself has surfactant
qualities. A saponifier will not react with a diol so would not do anything.

Ideally, an SIR test after cleaning would be good confirmation but, at
the least, a thorough electrical testing should be done, preferably in a
climatic chamber.

Brian

Bev Christian wrote:
> Technettters,
> Say you had a populated, expensive circuit pack that had been contaminated
> with ethylene glycol.  Would you chuck it or clean it?  I seem to recall
> that before I entered the industry that there was a time when some type of
> glycol was used on making printed circuit boards(?).  The reason I mention
> this, is if this were true, can glycols chemically bond at room temperature
> to PCBs by more than hydrogen bonding, to the point where a water wash,
> saponified or not, would not be able to remove the glycol.  I am assuming
> there are no standoff issues.
>
> regards,
> Bev Christian
> Research in Motion
>
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