Daan,

Dry Film soldermask (DSM) was the state of the art in the late 80's early
90's - before screenable LPI masks were developed. This mask will perform
nicely but is not as robust as LPI's.  The weak point is adhesion to copper,
and if the copper is not prepped well, the mask will fail. Some shops prep
the surface of the copper by using a black oxide or oxide alternative- the
same process they use for innerlayer bond enhancement.

DSM is  also REAL EXPENSIVE when compared to LPI.  If there is no driving
need for this mask (tenting vias for example) I would suggest changing to a
more modern LPI. If you are using this for via tenting there are some
alternate methods your board shop should be able to help you out with.

One other thing, as opposed to LPI's, your cleaning process can strip the
mask.  Both solvents and water based cleaners can cause the mask to lift.

Good Luck,
pete

>From: Daan Terstegge <[log in to unmask]>
>Reply-To: TechNet E-Mail Forum <[log in to unmask]>,              Daan
>Terstegge <[log in to unmask]>
>To: [log in to unmask]
>Subject: Re: [TN] Solder resist inspection underneath components
>Date: Tue, 23 Nov 2004 15:22:18 +0100
>
>Hi Steve & other Technetters,
>
>From all the uncoated boards of this batch we have removed a component
>to see which state the soldermask is in. 50% was very bad, the other 50%
>has the problem just a little bit on the outer edges of the
>solderresist. All of these are from one single datecode of bare boards,
>other datecodes are perfect. That's why we expect that 50% of the coated
>boards have the same issue.
>A question that I have is how bad it actually is to have this quality
>of soldermask (it has lost adherence and is flaking off) when the boards
>are parylene coated. Any opinions on this?
>
>Daan
>
>B.T.W.  I searched the Technet archives for "Dynamask" and all subjects
>that I found were about flaking of soldermask. Nice mask this is!
>
>
>
>
> >>> <[log in to unmask]> 11/22/04 11:59pm >>>
>
>Hi Daan!
>
>I'm sorry, I can't give you any ideas of how you'll be able to inspect
>
>beneath the components reliably for the integrity of the soldermask.
>
>I do have a couple of questions, how do you know it's only 50% of the
>
>boards? To me, if you have that high of a percentage of boards that
>have the  issue,
>I would be suspect of them all. Do you know what the cause is of the
>mask
>flaking?
>
>I have had my soldermask issues, and all of them without question have
>
>occured with dry films. I have had Dynachem (now Shipley) 5040 flake
>from  all the
>copper surfaces. This was because it doesn't hold up well against the
>Kyzen
>Aquanox that we use to clean our assemblies. I've posted a couple of
>times  to
>the Technet when this has happened to me.
>
>What do you use to clean your assemblies with?
>
>Sorry couldn't have of more help...
>
>-Steve Gregory-
>
>Hi  Technet,
>
>I have a problem with  a batch of boards of which I know  that an
>estimated 50% of them have a problem with the soldermask. The  mask
>(Dynamask 5040 dry film) is flaking off the board, and we didn't
>notice
>this because the mask is only applied underneath the components (and
>all
>of them have a low standoff, which makes it impossible to  inspect).
>Now we need to  know which of the boards are affected, but
>desoldering
>some of the parts to take a peek is not an attractive option as  these
>boards are already parylene coated.
>
>I'm quite convinced that  the answer is "no", but still I'd like to
>give
>it a try and ask the  following question:
>Does there exists ANY technology (non-destructive) that  makes it
>possible to inspect the quality of the soldermask underneath
>components?
>
>Best regards,
>
>Daan Terstegge
>PCB Assembly  Department
>Thales Land & Joint Systems
>
>Tel       +31(0)35 524 8297
>Fax       +31(0)35 524  8181
>[log in to unmask]
>Unclassified  Email
>
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