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December 1998

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Subject:
From:
Mark Simmons <[log in to unmask]>
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Date:
Wed, 2 Dec 1998 10:01:49 -0800
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I never for one minute considered that anyone was still building SMOTL
(Solder Mask over Tin Lead)  Apparently it is still common in the UK.

When i said that Fused T/L was more expensive to process, I was thinking
of SMOBC (Solder Mask over Bare Copper) with either selectivley plated
or stripped T/L, which had a spurt of approval in the '80's. (very few
shops could pull it off.)(plugged or reduced diameter holes was the
killer issue).

Werner, having been specialized in the HASL process for 12 years, I must
say, your understanding of the process is amazingly good. TechNetters
are well advised to listen activley when you speak about the process.
Kudos.

Related Notes:  When i started with the leveling service in '78, the
biggest part of the biz was re-working T/L plating.  usually because of
low deposits and de-wetting probs.  As Werner indicated, HASl is the
only
finish that accuratley previews the coppers solderability. This is due
to the passive nature of application.  The copper must accept the metal.

Also, as i may have said in the past, all that glitters is not HASL.
There is a wide variety of equip. in the field. Vertical and Horizontal.
Not all have the same level of control. The two primary vendors for the
Horizontal process, are Halco and Cemco. Non coverage, exposed Cu after
the first pass has always been an issue with SMT and i suspect this is
the main reason for multiple passes. Afri hit all the right buttons when
he described his efforts to minimize the problem.  Maintanance is
paramount to process control.  There are also significant design
differnces between these two above mentioned OEM's but thats another
story.

Sorry for the diatribe, but this is important stuff.

Mark Simmons

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