Guenter,
Here is my two cents (2/100 euro) on part of your discussion. I
worked for a thick film contract house for a while and we always used
solder with some silver in it to slow down the diffusion process
(leaching) of the thick film. The 62/36/2 alloy worked great. We also
used a 95/5 alloy that I believe is 96.5 wt.% Sn and 3.5 wt.% silver.
This had a melting point of 221 degrees centigrade. It worked quite
well in production as long as the surface mount components could
withstand a higher peak reflow temp of around 250 centigrade. There
were two designers that had been with the company for 20 or 30 years and
when I asked them why they would spec out one alloy and why the other
alloy, the reply was always that the 95/5 alloy was 'too brittle' and
could not withstand thermal cycle. It seems that everything gets
thermocycle, so I think it was the range or number of thermocycles that
the product had to withstand that was important in determining which
solder alloy could or could not be used.
Regards
Wade Oberle
[log in to unmask]
P.S. Steve and the guys, keep up the stories. I'm compiling a book of
bed-time stories for children of technoheads (GRIN).
-----Original Message-----
From: Guenter Grossmann [SMTP:[log in to unmask]]
Sent: Tuesday, February 02, 1999 6:56 AM
To: [log in to unmask]
Subject: [TN] Lead removal again
Hi Ed
The question is about alternatives to what we are talking.
1) Alternatives to HAL
2) Alternatives to Tin/Lead solder
And combinations of both
Now, since Bob asked me what pad surfaces I tested let me begin
with these:
I am sure that a lot of new surfaces are around. OSP's, NiAu,
Omicron, Alphalevel are about the ones I know of ( hey Bob since you are
reading this too, that might be the slot for your 2 cents ).
We did test OSP ( don't want to mention a brand name), NiAu (
but that's 5 years ago and the Au thickness was not very well controlled
), galvanic tin and solid solder deposition ( SIPAD ).
The test we run was -20/100 deg. C with a gradient of 2 deg C
/minute and dwell times of 30 minutes.
We removed the specimen from the test chamber after 4000 cycles
and compared the crack length in the solder joints of some components
with those on HAL. OSP's and NiAu showed a higher average crack length
than HAL, Sipad or tin. But again, these data are not suitable for a
reliability prediction since they don't allow it to make a statement
about the evolution of the damage.
Alternatives to Tin lead solder many too. And also lots of
problems are there , as Oxonfenuk ( sorry fella didn't get your
Christian name on the mail ) pointed out. Just imagine all the world
would start to solder with any Indium solder. I'm sure the world
recourses wouldn't last long. There are Tin-Copper , Tin-Silver binary
alloys but they all tend to have a high liquidus temperature. So ternary
alloys are used ( Tin/Copper/Silver, Tin/Silver/Bismuth etc.) to lower
the melting temperature. I have no data in hand but you see, one big
advantage of Tin/Lead solder is its ductility which allows it to combine
materials with high differences of the CTE. Maybe Bob Willis or Collin
Lea of ITRI ( are you on the Net Collin?) could give some contributions.
Principally there are now problems to be expected with the use of
ternary alloys ( Sn62Pb36Ag2 is a ternary alloy too ).
I believe that alloys on tin/copper or tin/silver base can meet
the demand of the world market.
I don't know whether anyone made thermal cycling tests with new
alloys. I mean thermal cycles not thermal shock, nor do I know who made
research on the deformation/degradation behaviour of these alloys.
I think the fluxes are not a big problem. What I see so far, tin
will be the main content of all lead-free alloys. And all the surfaces I
saw so far work well with fluxes used presently.
Best regards
Guenter
################################################################
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 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
################################################################
################################################################
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
################################################################
|
