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January 2007

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Subject:
From:
"Dehoyos, Ramon" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Dehoyos, Ramon
Date:
Wed, 3 Jan 2007 13:29:17 -0500
Content-Type:
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text/plain (154 lines)
	I would say that temporary masking would be needed mostly
through the wave and not through the reflow, since the paste is placed
in places where solder is needed with exceptions such is via in pad.
	Ramon 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Wayne Thayer
Sent: Wednesday, January 03, 2007 11:18 AM
To: [log in to unmask]
Subject: Re: [TN] Temporary peelable solder masks

Printed peelable mask is generally incompatible with SMT because it
interferes with the solder stencil if it's thick, and if it's thin it
can be very difficult to remove.  Probably less printed peelable in the
US reflects a higher proportion of SMT boards built here.

Wayne Thayer

>>> [log in to unmask] 1/3/2007 10:43:45 am >>>
Peter,
          I guess in part that is what I am asking. Do US assemblers
more commonly use the in-house/DIY approach rather than have the PCBs
supplied with the masking pre-applied to a supplied (gerber layer?)
pattern. Alternatively I know that some use masking that is removed by a
post-wave-solder cleaning process rather than peelable. Just surprised
that what our suppliers seem to think is not a big problem to provide as
a normal service is apparently not so readily available in USA... Or
maybe it just depends who you ask!

Cheers


Nigel Burtt
Production Engineering Manager
Dolby Laboratories, Inc. - European HQ
Email: mailto:[log in to unmask] 
Tel:     +44 (0)1793 842132 [direct line with voicemail] 
Fax:    +44 (0)1793 842101

 

-----Original Message-----
From: Peter Swanson [mailto:[log in to unmask]]
Sent: 03 January 2007 15:37
To: TechNet E-Mail Forum; Burtt, Nigel
Subject: RE: [TN] Temporary peelable solder masks

Nigel,

You rightly draw the distinction between a) the types of temporary masks
which are pre-applied by screen printing, usually by the pcb fabricator
and b) the temporary masks which are dispensed on by the guys doing the
assembly. They are different.

Whilst it is obviously desirable to have this job done by your fab guy,
as you pointed out, it isn't always straightforward. In particular, I
remember a few years back when the process window on the screenable
materials wasn't very wide, resulting in problems from under/over cure,
removal, etc. Maybe the formulations are more robust today.

It is possible to make the "in-house" dispensable types more appealing.
Dispensing can be by fairly inexpensive robotics. Curing can be quick by
heat or UV. Is this approach an option?

Regards,
Peter
--------------------------------------------------------
Peter Swanson           [log in to unmask] 
INTERTRONICS                http://www.intertronics.co.uk 
Tel: +44 1865 842842                   Oxfordshire, England

INTERTRONICS is dedicated to providing quality material, consumable and
equipment solutions to the high technology, high performance assembly
industries, incorporating outstanding levels of technical support and
customer service.

Read our blog! http://www.intertronics.co.uk/blog/blog.htm 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of N Burtt
Sent: 03 January 2007 09:27
To: [log in to unmask]
Subject: [TN] Temporary peelable solder masks

I'm being told that these are not widely used in USA, the common types
used here in the UK (Peters and Electramask) not readily available, and
they create packaging and shipping problems... thus US PCB suppliers
reluctant to supply PCBs with peelable masking applied. Is this true?

Now they are by no means a perfect solution to protecting holes on a PCB
during wavesolder, but am not aware of another way of doing so in a
no-clean RoHS process if fixturing can't do it. What do US PCB
assemblers do if pre- applied peelable masking is really not viable?
Other ideas?

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