Hi Gerry - I suggest that you take a look at  the following paper:

"The Root Cause Failure Mechanism for Solder Joint Integrity of Electroless
Nickel/Immersion Gold Surface Finishes", Nicolas Biunno, IPC Expo
Proceedings, paper S-18-5

There have been some instances where the Immersion Au/ Electroless Ni has
been a problem finish for some assemblers. The paper details some possible
reasons for those reported problems.  I have not experienced any problems
with the use of Immersion Au/ Electroless Ni finishes but I am also using
it in some very specific product applications. The Immersion Au/
Electroless Ni is very flat thus making placement of fine pitch and area
array components much better than a HASL finish. Good Luck.

Dave Hillman
Rockwell Collins
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"Gerald G. Gagnon" <[log in to unmask]> on 04/14/99 09:54:47 AM

Please respond to "TechNet E-Mail Forum." <[log in to unmask]>; Please respond
      to "Gerald G. Gagnon" <[log in to unmask]>

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cc:
Subject:  [TN] Assembly process differences between HASL and nickel/gold
      surface              finishe




Hi Technet!

Another one of those days.....

Here's my scenario:

I'm trying to design a large (18"X20"), thick (.120") complex (20+ lyr)
PWB which has two very large Land Grid Arrays (1500 pins ea.) requiring
hard nickel gold.

While the CAD routing is going on, my preference is to design the thing
using  nickel/gold as the surface finish to avoid many, many issues for
PWB mfg. We need it anyway for the LGAs.

I see boards like these (i.e. all nickel/gold finish) all over the place
when I visit board shops. Although I see some selective HASL with
nickel/gold too, NONE of the board shops want to do this and price it
accordingly.

HOWEVER, the assembly group I have to use has been using HASL for the
last 8 years but took 12 years to convert from plated reflowed tin/lead
to HASL ! I was the bozo that hung in there for the 12 years!

Nickel/gold would be a very convenient surface finish solution.

I don't have another 12 years fight left in me!

From the assemblers:

What are the SMT process differences between a HASL version (assuming it
could be built) and the nickel/gold version?


Thanks for anything that helps....

Gerry

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