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January 2007

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Subject:
From:
"Barmuta, Michael" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Barmuta, Michael
Date:
Thu, 4 Jan 2007 10:11:40 -0800
Content-Type:
text/plain
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text/plain (161 lines)
Graham: The peelable vinyl's are very stable after application and cure
prior to soldering. Six months+ should not be a problem.

The water soluble masks are a different story. The are hygroscopic by
nature. If they are not properly stored the coating will begin to
breakdown, soften and stick to adjacent surfaces. We normally don't hold
water soluble boards longer than a month. However by using special slip
sheets, packing and storage conditions we have held them up to a year,
but I wouldn't recommend it for normal production.

	
Regards
	
Mike B.
	
Fluke Corp.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Graham Collins
Sent: Thursday, January 04, 2007 9:49 AM
To: [log in to unmask]
Subject: Re: [TN] (2)Temporary peelable solder masks

Hi Mike!
Thanks for the detail.  Interesting.  What sort of shelf life would you
expect on a bare board with a vinyl mask on it?  



regards,

Graham Collins
Process Engineer, 
L-3 Communications Electronic Systems Inc.
Halifax
(902) 873-2000 ext 6215

>>> "Barmuta, Michael" <[log in to unmask]> 01/04/07 11:41AM >>>
Graham: As an OEM that has built both bare boards and PCA's and used
temporary soldermask resist (TSR) for 30+ years, let me address a
couple
of your questions.

*	Bare board fabricators do apply peelable TSR, however there is
not a large demand for it. So finding a shop that offers it may be a
little difficult.
There are two main types of peelable TSR, latex based and vinyl based.
Typically the fabricators apply the vinyl style. It is applied to the
board with a squeegee by printing thru a screen imaged with the
features
open to where the mask is desired then baked to cure. 
It works well if applied correctly, cured correctly and the printed
feature has the right design/shape. If done improperly it is a mess.
Hard to remove, breaking into small pieces, very labor intensive for
removal.


*	If using a water soluble TSR use an unfilled version. Some TSR
manufacturers add fillers such as talc or silica  to there products to
enhance the printing or rheology characteristics. Unfortunately as you
found out it tends to clog filters, wear nozzles/pumps, settle in low
spots, etc. Unfilled TSR's do not have this problem there are 100%
soluble. As I said above we have used TSR for 30+ years in our aqueous
wash system and not had any problems with the equipment.

	

	
Regards
	
Michael Barmuta
	
Staff Engineer
	
Fluke Corp.
	
Everett WA
	
425-446-6076
	


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Graham Collins
Sent: Thursday, January 04, 2007 6:57 AM
To: [log in to unmask] 
Subject: Re: [TN] Temporary peelable solder masks

Similar to Steve, our military stuff always gets cleaned.  But I did
build some class 3 stuff with no-clean - mainframe equipment
(commercial) - with a previous employer.  Your bank wants class 3
product and very high reliability, but at least you can count on them
to
not use a hose to clean it off, and they keep the office
air-conditioned.  
Given that at this employer we do contract manufacturing, the
likelihood of convincing all customers to agree to no-clean flux is
fairly slim and so it's difficult to justify looking at the
qualification work.  We also have the issue of supporting build over
many years, which often forces buying "end of life" batches of parts -
which become more difficult to solder over time, so a fairly active
flux
is required.

If I'm understanding Nigel's question properly, I'd never heard of a
PWB manufacturer pre-applying peelable solder mask - it's not
something
I've ever come across as an option.  Does it work well?  How does the
PWB manufacturer apply it?  

We use the DIY version, we apply it just before wave soldering.  We
currently use the peelable stuff, we had used the water soluble but
with
some production volume increases we were finding it clogged up the
filters in the cleaners too quickly.  

regards,

Graham Collins
Process Engineer, 
L-3 Communications Electronic Systems Inc.
Halifax
(902) 873-2000 ext 6215

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