While it certainly true that poor quality leveling is at the root of the
flatness problems associated with HASL Bob, it's also true that lead free
alloys can provide a tighter thickness range.
XRF thickness measurements taken from a broad range of panel types coated
here recently (with a Ni stabilized SnCu solder in a Horizontal system)
resulted in a range of 3 to 8 microns. That is to say the 'swept' leading
edges of larger features and earth plain areas were typically 2-3 Microns;
where we would have expected to see 1-2 microns with SnPb. Small bga pads
and trailing edges of 'awkward' features that can be as high as 25 microns
with SnPb measured 8-9 microns. The range will certainly we wider with
vertical systems (due to the panel fixturing system restricting panel
placement accuracy and proximity) but it can still be significantly
'flatter' than with SnPb. We are about to repeat these trial with a Ag
stabilized SnCu and a 3% SAC. If anyone is interested in participating in
these trials please contact me.
-----Original Message-----
From: Bob Willis [mailto:[log in to unmask]]
Sent: Sunday, June 27, 2004 6:15 PM
To: [log in to unmask]
Subject: Re: [LF] Lead-Free HAL
I would agree with the points raised, it will not be better than tin/lead
for flatness it will be equal to. Howerver if people treat this as a new
process they may speand a little longer setting up the process and achieve
better results.
I have a number of images of boards and the thickneess measurments for the
boards we assembled.
Many thanks
On 6/27/2004, "Bob Gilbert" <[log in to unmask]> wrote:
>David,
>The nickel stabilized tin/copper alloy, SN100CL has been available for
>lead free HASL coatings by 2 P.C. Fab shops in Europe for the last
>year. Being reverse compatible, the 2 companies have switched to it as
>their standard
HASL
>offering.
>In addition, Florida Cirtech is working with a number of board shops in
>the U.S. so they can offer a HASL option for the new lead free
>requirements. We now have one company in the Chicago area manufacturing
>lead free HASL boards with the SN100CL alloy in a vertical HASL
>machine. In addition, we have another board shop in the Dallas area
>having a horizontal machine being converted this summer and should be
>in operation by
August.
>I would be happy to assist anyone in having test boards coated for
evaluation.
>The many advantages of the nickel stabilized tin/copper alloy for wave
>soldering over the SAC alloys also play a role in its success as a HASL
alloy. There
>is even evidence that it may have a better shelf life than tin/lead and
also
>give a flatter surface than tin/lead HASL.
>
>Sincerely,
>Bob Gilbert
>Technical Sales Manager
>FCT Assembly, Inc.
>970-346-8002
>
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>
Bob Willis
2 Fourth Ave, Chelmsford
Essex, CM1 4HA England
Tel +44 01245 351502
Fax +44 01245 496123
Web www.leadfreesoldering.com
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