Hi All,
1st Technet posting so apologies if format is wrong.
I have read a number of studies showing that SN62 alloy is superior in fatigue
failure (and thermal cycling) to 63/37. (eg "Fatigue Failure in a model SMD
joint" Tin Research Institute 1989).
"....this is interpreted as the precipitated Ag3Sn phase decreasing the
recrystallisation rate within the lamellar structure"
And again in "Reliability of soldered joints: A description of the state of
the art" Philips SMD manufacturing technology centre.
However I'm perfectly happy to stand corrected; the best article I found on
SMD failure modes generally, was by one W Engelmaier, "Surface Mount Solder
Joint Long-term reliabilityy: Design, testing, prediction" 1989! So I'm
amongst my superiors!
cheers
Greg Major
Quoting Werner Engelmaier <[log in to unmask]>:
> Hi Steve,
> First, I said 'most' not 'all.'
> Second, 'tombstoning' was not mentioned--I think; and tombstoning can
> get solved by other means.
> Third, Günter already gave a good explanation--you would get the same
> effect if you go off-eutectic with SnPb.
> Werner
>
> -----Original Message-----
> From: Blair K. Hogg <[log in to unmask]>
> To: [log in to unmask]
> Sent: Thu, 18 May 2006 12:10:00 -0400
> Subject: Re: [TN] Antw: Re: [TN] 62Sn/36Pb/2Ag solder - too good to be
> true?
>
> Isn't that why they add the silver?
>
> Blair
>
> >>> [log in to unmask] 05/18/06 10:35 AM >>>
> 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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