Steve
I think this is not because there was silver in the solder paste but because the SnPbAg was rather far away from the eutectic thus disabling an instantaneous melting of the solder depots.
Guenter
EMPA
Swiss Federal Laboratories for Materials Testing and Research
Centre for Reliability
Guenter Grossmann, Senior Engineer
8600 Duebendorf
Switzerland
Phone: xx41 1 823 4279
Fax : xx41 1 823 4054
mail: [log in to unmask]
>>> [log in to unmask] 18.05.2006 15:16 >>>
Hi Werner!
Lord knows that you have probably forgot more than I'll ever know, and I
respect you and your vast knowledge and experience. But this one time
I'm going beg to differ on one of those "Urban Myths"...
I do know, from experience, that a 2% silver will help reduce, if not
eliminate tombstones, I've seen it work. There were two assemblies in
the very recent past that I have experience with. On one assembly, we
had unbalanced traces on 0402's on the backside that would tombstone
constantly. When I would use the 2% silver solderpaste, the tombstoning
would be be completely eliminated. We might have seen 1 or 2 on a board
or two every once in a while.
On the other assembly all the 0805 locations had the gap between the
pads laid-out at 1.27mm (.050") and we were getting a lot of
drawbridging and tombstones. First pass yeild was well under 50% at
reflow. With 2% silver paste we had the same results, tombstoning and
drawbridging was practically eliminated.
Trust me, when we would build a board that would exhibit tombstones, I
would first look at paste deposition to make sure the print was good,
then check placement to make sure it was accurate, and then look at my
reflow profile. If after all that I couldn't solve the problem, I would
go to a 2% silver paste and most of the time it would greatly reduce if
not eliminate tombstoning.
Maybe this is good challenge for the "Mythbusters" TV show...hehehe.
-Steve Gregory-
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Werner Engelmaier
Sent: Wednesday, May 17, 2006 7:50 PM
To: [log in to unmask]
Subject: Re: [TN] 62Sn/36Pb/2Ag solder - too good to be true?
Hi Jeff,
Most of what you list as advantages are 'urban myths.'
Werner
********************************************************************
>Hi everyone,
>Lead free aside, what are the disadvantages of using 62Sn/36Pb/2Ag
solder?
>I have only ever heard good things about it, such as reduced leaching
of silver and gold, phased reflow, improved joint
>appearance, and a few other things that I can't recall. It is even the
same price as 63/37, and I have used it myself
>with good results.
>However, if it were so universally fantastic, no-one would use
63Sn/37Pb or 60Sn/40Pb, but lots of people do. What's the >catch?
>Thanks,
>Jeff Brown
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