TECHNET Archives

1995

TechNet@IPC.ORG

Options: Use Monospaced Font
Show Text Part by Default
Show All Mail Headers

Message: [<< First] [< Prev] [Next >] [Last >>]
Topic: [<< First] [< Prev] [Next >] [Last >>]
Author: [<< First] [< Prev] [Next >] [Last >>]

Print Reply
Subject:
From:
[log in to unmask] (Guenter Grossmann)
Date:
Wed, 6 Dec 1995 11:16:15 +0100
Content-Type:
text/plain
Parts/Attachments:
text/plain (36 lines)
We where looking at this two years ago. A company working in
telecommunication asked us to qualify this process, because it is very
convenient to have gold plated pads if the contacts for the dialling
contacts must be gold plated too. We had several PCB's produced. Some with
gold plated pads, some with HAL surface and some with an organic coating of
the pads. These specimen where subject to thermal cycling. ( -20°C / 100°C;
80°C / min.; no dwell time ). The results of the crack propagation was,
that after 10'000 thermal cycles the solder joints on gold plated pads
showed cracks approx. 2x longer than in the solder joints on HAL pads those
in the joints on pads covered with organic compound had cracks approx. 2.5x
the cracks in the solder joints on HAL pads. Microsections showed some AuSn
intermetallich compounds and SnNi Intermetallics. No reidues of the gold
layer where visible.Note, that we have no information how thick the Au
layer was. It war sold as "Gold Flash on Nickel", whatever the PCB supplier
meant with that term. However, we suggested, that the technology would be
adequate for indoor telecom equipment since the thermal stress is not as
severe as tested. Problems occurred after one year, when the company
switched the entire production to the Gold plating process. One customer
decided to place a telephone switching box outside. After one winter the
equipment failed and when the box was opened there was heavy rainfall of
components off the vertical mounted PCB.The rupture surface showed lots of
AuSn and NiSn intermetallics. Unfortunately we could not organise
additional founds to continue with our research in this field. In the
meantime we successfully produced 500 PCB's with a testpattern containing
0.5mm pitch QFP's and HAL pads. The stencil printing was tricky but well
possible. Right now we work on 0.3mm but it seems as if HAL is difficult to
print.

G.Grossmann
[log in to unmask]






ATOM RSS1 RSS2