Kelly,
I must challenge your statement:
> "be applied satisfactorily over the
> leavings of low residue flux, or any other residue, could only be
considered
> valid if the conformal coating had been retested and passed the
> qualification requirements of IPC-CC-830, MIL-I-46058, or whatever
> specification"
This is misleading as it implies that any coating so tested is OK to apply
over no-clean. NOT SO! These specifications require testing of the material
on its own, in isolation on coupons that have been cleaned until they
squeak - there shall be no flux present!
In order to successfully coat over no-clean - and it can be done - you MUST
test the entire process with totally representative coupons of YOUR process.
Consider that a conformal coating is a permanent product to do a permanent
job and seals in as well as out and bingo - if you have something nasty
underneath, then it matters not one jot the specification approvals the
coating may have.
I repeat, it can be done, but I did not say it was easy or straightforward.
Regards :-)
Graham Naisbitt
[log in to unmask]
WEB: http://www.concoat.co.uk
CONCOAT Ltd
Alasan House, Albany Park
CAMBERLEY GU15 2PL UK
Tel: +44 (0) 1276 691100 Fax: +44 (0) 1276 691227
----- Original Message -----
From: Kelly M. Schriver <[log in to unmask]>
To: <[log in to unmask]>
Sent: Monday, March 20, 2000 12:29 PM
Subject: Re: [TN] Coating of assemblies with no clean fluxes
> Mornin' Grant & All -
>
> The argument that conformal coating can be applied satisfactorily over the
> leavings of low residue flux, or any other residue, could only be
considered
> valid if the conformal coating had been retested and passed the
> qualification requirements of IPC-CC-830, MIL-I-46058, or whatever
> specification is valid in the case of that material.
>
> IMHO, any statements by the formulator of any of the materials which are
not
> supported by this data would have to be considered trivia. I think we've
> all seen the cases of vessication, where the water molecule has passed
thru
> the vapor permeable barrier of the coating and attached itself to a
> contaminant on the surface of the board, creating a microscopic cluster of
> bubbles. That is just one example of what may take place.
>
> Regards - Kelly
>
>
> -----Original Message-----
> From: Grant Emandien <[log in to unmask]>
> To: [log in to unmask] <[log in to unmask]>
> Date: Monday, March 20, 2000 3:29 AM
> Subject: [TN] Coating of assemblies with no clean fluxes
>
>
> >Hi all,
> >
> >The debate on cleaning of fluxes as well as the use no-clean fluxes seems
> to
> >hang around forever. We have been informed by our solder an flux supplier
> >that assemblies with no clean fluxes can be conformally coated without
the
> >need to clean the boards.
> >
> >The argument is that the high temperatures of the reflow oven 'burns off'
> >the active ingredients, leaving only inactive residues. These flux
residues
> >do not have to be cleaned and can supposedly be coated. The rep. believes
> we
> >are taking a backward step by possibly opting to use water-based flux. Is
> >this pure sales talk?
> >
> >Is anyone able to offer any advice or insight, or been able to assess the
> >environmental and electrical performance of such assemblies.
> >
> >Regards
> >Grant
> >
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