In Reply to David's question: My understanding is that it has to do
with the assembly/soldering process used to assemble the board. Many
if not most of the components that are being soldered with higher
temperature solders today are soldered by hand or wave soldered. The
leads see the higher temperature but the main body of the component
does not. The problem starts when you consider reflow soldering where
all of the component, in fact the entire board assembly has to be
exposed to to the maximum reflow temperature of the solder. As it
has been pointed out, due to production variables, this is usually 40
to 50 degrees above the solder melt point. So with SN63 and the like
solders this is usually around 215 C. If we have to start using no
lead solders that melt at 220 C or so then we are looking at doing
reflow soldering at 260 C or above. The other factor that no one
seems to be seriously considering yet is the time spent at this
temperature. 30 or 60 seconds at 260 C is likely to be very damaging
to most plastic IC's.
Rick Etchells
Schlumberger
>How do the majority of manufacturers spec in components used in high temp
>applications today? I see quite a few orders of high temp solder (Au/Sn,
>Sn/Ag, Sn/Sb, CASTIN, high Pb alloys, etc.) go past my desk, and I wonder if
>steps are being taken currently by the users of these to ensure that
>component degradation will not occur. If so, I rarely hear about it.
>
>Basically, I'm saying/wondering/asking the following: high lead solders
>always have been relatively popular in electronics assembly, yet I have
>never heard a great concern about component reliability when used in
>conjunction with these (more like the passing question now and then being
>the exception rather than the rule). Why all of a sudden is there such a
>great concern? I can think of two very cynical answers: 1) Assemblers have
>been lax in the past, or 2) This really is not such a major issue, and
>people are just naturally fearful of change (i.e. removing lead from
>solders).
>
>I am not saying that I necessarily agree with either of the above, or that
>this is not an important issue. I'm just curious if anyone else has had
>these same thoughts, and/or if anyone could explain the above phenomenon, or
>if perhaps I'm just crazy.
>
>Please keep the flames to a minimum!
>
>Thank you and best regards,
>
>David Suraski <[log in to unmask]>
>Technical Marketing Specialist
>AIM <www.aimsolder.com>
>Tel: 401-463-5605/1-800-CALL-AIM
>Fax: 401-463-0203
>
>
>
>-----Original Message-----
>From: Brooks, Peter <[log in to unmask]>
>To: [log in to unmask] <[log in to unmask]>
>Date: Tuesday, August 17, 1999 10:13 AM
>Subject: Re: [LF] Survival of Solder in Components
>
>
> >Marty:
> >
> >In answer to you e-mail message.
> >
> >The concenus appears to be that there is no good replacement for the high
>lead
> >(95Pb5Sn) alloys used for die attach of power transistors at this time.
> >
> >Regarding the assembly peak temperature profile the concenus appears to be
>that
> >while it can be done at say 240 degrees it doesn't allow for production
> >variations. I looks as if temperatures of 255 -260 max are being forced on
>the
> >component suppliers.
> >
> >Pete Brooks
> >Intersil Coporation
> >
> >
> > -----Original Message-----
> > From: Martin Weiser [SMTP:[log in to unmask]]
> > Sent: Sunday, August 15, 1999 5:54 PM
> > To: [log in to unmask]
> > Subject: [LF] Survival of Solder in Components
> >
> > Back in mid-July David Suraski asked about what implications the
>higher
> >reflow temperatures for boards would have on the components. There was a
>great
> >deal of discussion (I just finished reading 30 days worth of posts) can be
> >summarized as:
> > 1. The component temperatures don't have to be that much higher
>(peak
> >of 220C - 240C) if one is very careful about the thermal profile and
>atmosphere.
> > 2. There are a few components where even these temperatures will
>be
> >problematic.
> > 3. Conductive polymers will solve some of the problems in case 2.
> >
> > I am a bit concerned about the second case since we supply solders
>for
> >die attach in power products. Generally these solders must have both high
> >thermal and electrical conductivity since these devices often dissipate as
>much
> >as 10 to 50 W. The most common solders for these applications are high-Pb
> >(Pb5Sn, Pb5Sn2.5Ag, Pb2.5Ag2Sn, etc.), Sn25Ag10Sb, and Sn8.5Sb. There are
>two
> >Pb-free alloys in this list (and they are used extensively), but they have
> >solidus temperatures of 228C and 236C respectively (our customers have
>asked
> >about reflow at 270C). We have looked at the problem a bit, but there are
>no
> >straight-forward solutions that are also inexpensive. A Japanese group
> >presented at the TMS annual meeting on an Al-Zn-Mg-Ge alloy, but their
>results
> >were not great. The other alternatives are the high-Au alloys like Au20Sn,
> >Au3Si, etc., but they are extremely strong and a bit more expensive than
>the
> >high-Pb alloys.
> >
> > Does anyone have any further comments along these lines? Ideas of
>how
> >the industry will approach the issue? It seems to me that most of the
>industry
> >emphasis has been on the board level solders where there appear to be a
>fair
> >number of workable solutions. However, most of these will push some groups
>to
> >components to their limits and beyond.
> >
> > Regards - Marty
> >
> > Martin (Marty) Weiser, Ph.D.
> > Product Manager - Plated & Discrete Products
> > Johnson Matthey Electronics
> > Spokane, WA
> > (509) 252-2757 (phone)
> > (509) 252-8617 (fax)
> > [log in to unmask]
> >
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_________________________________________________________________
Rick Etchells
SPC Packaging & Characterization
200 Gillingham Lane, Room 713
281-285-4449 (office)
281-285-4133 (fax)
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Assemblies.
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