Mike
The final results of the print reflow of a 6.5 mm diameter circle of SAC
paste appears to be a circle of (as near as I can tell) intermetallic about
8% larger in diameter than the print. This circle is a thin, slightly rough
silver coating on the copper.
Within the circle is a dome of solder that is aprox. 75% of the
intermetallic diameter. The wetting angle of this dome on the
"intermetallic" circle is something I haven't measured yet.
Let me see if I can get a picture or two. That may provide more accurate
info than my above description.
Greg
-----Original Message-----
From: Mike Fenner [mailto:[log in to unmask]]
Sent: Thursday, February 13, 2003 8:48 AM
To: [log in to unmask]
Subject: Re: [TN] IPC Test Question
Interesting. As Greg noted wetting angles and spread are not as good with
the high Sn lead-free alloys due to their higher surface tension. This means
that full pad coverage may not always be possible so some change in
inspection criteria is going to be required, no doubt this is in the
Committee's Agenda.
Dewetting - at least as usually defined for Sn/Pb - however is not the same
thing as low wetting and should not be an issue, this is not something we
have factored in in our own debates. Could Greg elucidate?
Regards
Mike Fenner
Applications Engineer, European Operations
Indium Corporation
T: + 44 1908 580 400
M: + 44 7810 526 317
F: + 44 1908 580 411
E: [log in to unmask]
W: www.indium.com
Leadfree: www.Pb-Free.com
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Wenger, George M.
Sent: Tuesday, February 11, 2003 1:08 PM
To: [log in to unmask]
Subject: Re: [TN] IPC Test Question
Greg,
I'm not sure how best to interpret your wetting/dewetting results. That
question is probably best answered by Dave Hillman's Soldering/Solderability
subcommittee. I think until you have a clear definition I'd measure the
area of both spread areas. I'd also suggest that you use a standard SN63
solder paste next to your Pb-Free paste so that you can get a baseline
comparison of spreading/dewetting/ etc. I know it is extra work and one
could argue that we'd never use the SN63 at the Pb-Free temperatures but it
might help provide some insight to the wetting/dewetting.
Regards,
George
George M. Wenger (908)-546-4531
Reliability Engineer
RF Power Amplifier Group
Andrew Corporation, 40 Technology Drive, Warren, NJ 07059
[log in to unmask]
-----Original Message-----
From: Munie, Gregory [mailto:[log in to unmask]]
Sent: Monday, February 10, 2003 2:40 PM
To: [log in to unmask]
Subject: [TN] IPC Test Question
Does anyone use IPC Test Method 2.4.46 for testing the wetting of solder
paste to copper coupons?
We are having an internal debate here over how to interpret "spread" for a
lead free alloy.
In general we get a "wetted area" larger than the print but there is
evidence of some pull back/dewetting, i.e. a dome of solder within a
somewhat larger dewetted circle.
As some Tin/Copper intermetallics are not easily wetted once they have
formed should the area of wetting be calculated on whole area covered or
just the solder "dome"?
At these lead free high temperatures how do I interpret wetting and
de-wetting from intermetallic formation?
Greg Munie
Kester Solder
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