Good question. We use mostly RMA, and clean after soldering with Bioact
EC-7R and DI water. We also clean just before conformal coat using 75%
IPA/25% DI water, in a batch system with in-process resistivity check. Our
ionic cleanliness is very good, typically around the equivalent of 1
mgNaCl/sq.in. As for organics, we've seen a few silicone-induced fisheyes
in the past, but our investigations found causes other than improper
handling.
Thanks to all for the help.
-Joe
> ----------
> From: Phil Bavaro[SMTP:[log in to unmask]]
> Reply To: TechNet E-Mail Forum.;Phil Bavaro
> Sent: Wednesday, November 24, 1999 2:50 PM
> To: [log in to unmask]
> Subject: Re: [TN] Assembly With Gloves Or Finger Cots
>
> What you haven't provided us with is what type of assembly process you
> have. Do you clean after soldering or is a no clean facility? Do you
> also
> conformal coat the edges of the cards?
>
> If you do clean your assemblies (especially before conformal coating),
> then
> perhaps all contamination is getting washed off of the assemblies and
> there
> may not be any issue.
>
> If you do not clean your assemblies after allowing your operators to
> handle
> them without protection from contamination, then I would be surprised if
> the assemblies can pass an ionics test consistently.
>
> Our policy is latex fingercots or esd-approved vinyl gloves because we
> have
> a high reliability based no clean soldering process and we find excessive
> contamination through ionics testing when improper handling (without
> protection) occurs.
>
> When installing fingercots, they roll them on and do not contaminate the
> clean surface on the outside. In addition, they discard them at every
> break/lunch/dinner.
>
> One day of an operator with silicone contamination on his/her fingertips
> will ruin one's whole week in a conformal coating operation.
>
> However, be careful in approving the fingercots and gloves which are
> touted
> to be static protective, as they must also be clean room qualified as
> well.
> Test, test, and test them some more.
>
> Phil
>
> At 11:02 AM 11/24/99 -0500, Kane, Joseph wrote:
> >Technetters:
> >
> >Our new Space customer may be pushing us to use static-protective gloves
> or
> >finger cots for soldering and assembly operations. We prefer to continue
> >our current practice, having operators exercise due care and handle
> product
> >by the edges only, and use gloves only for hot things or when using some
> >chemicals. This has worked well for all of our high-rel product,
> including
> >flight controls and aircraft engine controls. When we do 10-day humidity
> on
> >conformal coated assemblies, we occasionally see mealing patterns in the
> >shape of fingerprints, but not very often.
> >
> >Some of the problems we see with the alternatives, in approximate order
> of
> >importance:
> >
> >1. Gloves and finger cots compromise dexterity and tactile sensitivity.
> >Maybe not much, but some. Productivity suffers, defects go up, and maybe
> >some things get dropped that normally wouldn't.
> >2. Contaminants deposit on gloves or finger cots, obviating any benefit.
> >By contrast, when operators get flux or adhesives on their bare fingers,
> >they can feel it, and they go wash their hands, or at least wipe them on
> >something.
> >3. Finger oils still get on gloves or finger cots. You have to handle
> them
> >with bare hands to get them on, and then everyone's nose needs a scratch
> >once in a while.
> >4. Operators hate them because they are cumbersome and uncomfortable.
> Some
> >would say tough luck, and if there were good reasons we would force the
> >issue, but as it is this looks like another compliance issue/audit trap
> that
> >we don't really need.
> >5. Over time, some people develop sensitivity to latex, maybe even
> nitrile.
> >6. They cost money.
> >
> >Like bunny suits or respirators, I don't know why anyone would use these
> >things unless there was a good reason. Anyone out there have any
> >experience, good or bad?
> >
> >
> >Joe Kane
> >Lockheed Martin Control Systems
> >
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