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
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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
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-----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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