Hi Daan! We have successfully used HASL finished boards for the assemblies
which contain area array components - But - I would recommend that you
investigate the use of one of the new alternative board finishes (immersion
tin, immersion silver, immersion gold/nickel) as a method of improving your
assembly yields and eliminate soldering-ability issues. HASL has two
disadvantages working against it as a surface finish for area array
components; 1) the resulting HASL deposit on the pad is domed which can
lead to placement issues; 2) typically HASL deposit thicknesses can vary
greatly which can lead to soldering-ability issues. The advantage of the
new alternative finishes is their inherent flatness. However, unless you
live in the town of Perfect, the new alternative board finishes do not have
the same solderability robustness and suffer quicker thermal degradation
than a HASL board finish. We have migrated away from HASL board finishes to
the new alternative board finishes for designs incorporating area array
components and have been very satisfied with the results. We were just not
getting the consistency we expected/needed for area array components with
the HASL finish. Good Luck.
Dave Hillman
Rockwell Collins
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"d. terstegge" <[log in to unmask]>@ipc.org> on 10/31/2002
06:00:21 AM
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Subject: [TN] HASL process OK or not ?
Hi Technet,
Yesterday I visited one of our bare board manufacturers and had a close
look at their HASL-process. The reason for the visit was solderability
problems on BGA-pads, which sometimes look thin and dull. Occasionally
copper seems to be visible through the tinlead.
In general I think this is a very professional boardshop, but (being
not an expert) I don't know what to think about their HASL-process. I
hope someone on this great forum is willing to give me some input on my
findings, in terms of good or bad, or possibilities for improvement:
Machine: Quicksilver SM, vertical HASL, 250 kg solderpot, no preheat
Time between microetch (drying) and fluxing can be up to two hours
Solder pot temperature set to 255 °C
Leveling is done is such a way that the solder is as flat as possible,
although the design of the airknives causes a big difference betweeen
the two boardsides. With XRF we measured a thickness of only 0.4 microns
on BGA-pads, with about 3 microns on similar pads on the other
boardside.
Water-based flux from an open tank, without any composition control,
but tank is replaced every 24 hours.
Solder is replaced every 6 months, but except for copper contamination
no composition-check is ever done.
When copper is above 0.3 % the dross is skimmed off to assure that
copper content stays below 0.35 %.
Throughput of the machine is about 700 panels per day.
Daan Terstegge
Thales Communications
Unclassified mail
Personal Website: http://www.smtinfo.net
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