Todd,

I realise that this thread is weeks old but there does not seem to have been
any other response to your negative comment on lead-free HASL.

As has been mentioned several times in this forum, contrary to your summary
dismissal of the finish, lead-free HASL has now been established as a viable
process that has been demonstrated to have the capability of delivering a better
finish in terms of the smoothness and uniformity of the coating than tin-lead
HASL.    And, of the finishes you mentioned it has the capability of
delivering the longest problem-free solderable shelf life.  Further as a process that
leaves a stress-free finish it will not spontaneously generate whiskers.

When assessing lead-free processes one has to allow for the fact that the
process has to be optimised and for lead-free that means choosing the appropriate
alloy and ensuring that the equipment has the capability of working within
the smaller process window that is a dominant feature of lead-free technology.
 The pure tin that you say you used for lead-free HASL is not the best
lead-free material for the process.    You did not mention the equipment on which
the HASL finish was applied but much of the HASL equipment that has been running
with tin-lead solder does not have the capability of holding the tighter
process parameters required for lead-free.   I do not want to use this forum for
promoting particular alloys or equipment but am happy to provide some
information on alloys and equipment that is currently working successfully under
commercial production conditions to subscribers who contact me directly.   There are
companies who are happy to process boards on a trial basis for people who
want to evaluate lead-free HASL.

Keith Sweatman
Nihon Superior Co., Ltd

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