To: Pat Diamond

The query was can HMP solder be used to solder to a  connector pin well that
has 5 microns of gold plating for operating temperatures up to 275 deg. C..

Answers, if there are any:
With that much gold, soldering to the gold is not the problem when using the
HMP solders.  It only contains 5% tin.  Not enough to form the tin gold
intermetallic that is very brittle.  It is more likely to form the compounds
with high gold and low tin.  Thes are often very strong and also ductile. The
major problem is that the HMP solders, approx 92.5% lead, with a melting
poiint of 306'C-320'C, depending on the lesser material alloys added such as
silver or indium.  These solder do not take thermal aging very well.  The lead
crystals become coarse and are very prone to cracking even when subjected to
operating temperatures above 170'C for 8 hours or more.  If your joint is
subjected to any kind of stress, vibration or fatique, it will began to
develop cracks and major joint failures will occur.  I have not tried
temperatures of 275' C with these solders, but have tested the high lead
solders such as Pb95/Sn5, Pb92.5/Sn5Ag2.5, Pb90/Sn10, Pb97/Sn3, Pb95/Sn3/In2
up to operating temperatures of 225'C and found that they all had the same
characteristics, the lead coarsened after themal aging and cracks developed
with minimal stress.  However, if you have encapsulated the solder joint and
resteained its movement such as is often done with a connector, your risk is
much less.  The gold tin solder Au80/Sn20 has good properties up to 250'C but
has a 280'C eutectic melting temperature, a bit close to your operating
temperature and it very expensive.  It also solders to gold plating without
joint degradation.

Suggest you make up some samples, age them and give them the probable stress.
them send them Brian McCory of Delsen labs to do some metallography for you.
He has done considerable matallurgical evaluations of solder joints with the
high lead solder and gold plated land and leads on circuit boards.  He has
developed some good techniques for polishing and etching this combination in
solder joints.
.
Phil Hinton

################################################################
TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c
################################################################
To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body:
To subscribe:   SUBSCRIBE TechNet <your full name>
To unsubscribe:   SIGNOFF TechNet 
################################################################
Please visit IPC's web site (http://www.ipc.org) "On-Line Services" section for additional information.
For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312
################################################################