David:

I'm delighted you've weighed in with your excellent points. We can
always count on your for scientific approaches to issues too often
addressed via emotions.

As you've noted, many companies already set their wave solder
temperatures much higher than necessary (or desirable). They then
experience problems ranging from distortion of circuit boards to higher
component failure rates. When the new solders are implemented, it will
not be possible to reduce temperatures to the 450°F range that makes
sense with current tin/lead. And I fear that those companies already
running at excessive temperatures will, in their lack of knowledge, turn
the heat even higher.

Your other point about the higher tin content dissolving leads, end caps
and other metal parts is indeed cause for concern and not widely
recognized.

Summing up, then, it seems to me we end up with a process that is not at
all friendly to the components (regardless of whether the environment is
or is not better off). Would you concur? If not, what am I overlooking?

Jim Smith
Managing Director
Cambridge Management Sciences, Inc.
4285 45th St. S.
St. Petersburg, FL 33711-4431
Tel: (727)866-6502 ext. 21
Fax: (727)867-7890
eMail: [log in to unmask]



dsuraski wrote:
> 
> Actually, there are several companies out there running lead-free alloys in
> wave soldering at a "drop-in" temperature as compared to Sn/Pb.  The reasons
> for this are two-fold: First, many companies run Sn/Pb at a higher
> temperature than absolutely necessary.  The operating window for Sn/Pb in a
> wave is about 425 to 500F, but most companies are at the very high end of
> this (490-500+F).  In these cases, many lead-free alloys may be used at the
> same temp.  Basically, the temperature range for lead-free alloys begins
> where the range for Sn/Pb ends, and there normally is crossover (BTW, this
> also is often the case with hand soldering).  Second, one of the reasons for
> exceeding a solder's liquidus in wave soldering is to reduce the solder's
> surface tension sufficiently to promote drainage, etc.  As with SMT, the
> superheat temperature needed for most lead-free alloys is not as high as
> with Sn/Pb due to the surface tension characteristics of lead-free alloys.
> Therefore, it usually is possible to get by with a peak temperature only
> slightly above the liquidus.  As with Sn/Pb, though, a higher peak temp can
> promote better wetting.
> 
> As far as temperature concerns relating to lead-free alloys, the greatest
> emphasis should be placed on SMT.  My primary concerns for wave soldering
> relate to the high tin content of lead-free alloys, which tend to dissolve
> the standard materials in wave soldering machines now.  Specifying a
> "lead-free compatible" wave machine can help. Also, some alloys such as
> Sn/Cu offer poor wetting and sometimes require nitrogen and/or very
> aggressive flux chemistries to achieve adequate soldering.
> ----- Original Message -----
> From: "Jim Smith" <[log in to unmask]>
> To: <[log in to unmask]>
> Sent: Tuesday, December 05, 2000 1:16 PM
> Subject: Re: [LF] AW: [LF] Component Durability
> 
> Hans:
> 
> You've confirmed my worst fears. As I point out in my note to Doug Romm
> here, wave soldering (if it survives the change in alloys) is an even
> more hostile environment than reflow ovens. How (or can) we handle those
> conditions?
> 
> Jim Smith
> Managing Director
> Cambridge Management Sciences, Inc.
> 4285 45th St. S.
> St. Petersburg, FL 33711-4431
> Tel: (727)866-6502 ext. 21
> Fax: (727)867-7890
> eMail: [log in to unmask]
> 
> "" wrote:
> >
> > ----------
> > Von: jsmith / unix ([log in to unmask])
> > An: [log in to unmask]
> > Betreff: [LF] Component Durability
> > Datum: Montag, 4. Dezember 2000 22:03
> >
> > It is surely not the question, if component makers are able ore unable
> > to produce robust components (I´m sure they do their best), it´s the
> > simple physical limit: for all kinds of plastic capacitors the melting
> > point of the foil is not changeable, so this technology and industry
> > will be killed by the leadfree enthusiasts. Similar for the electrolytic
> > capacitors, the boiling temperature of the electolyte is not manipulable
> > as one wants. You mentioned the ceramics, it is also wellknown, that all
> > kind of ceramics are thermoshock sensitive, the higher the solder tempe-
> > rature, the higher the shock. Also the mismatch of the different expansion
> > coefficients, while the soldered component cools down on the board from
> > the higher soldering level leads to cracks. One question at the end,
> > if You buy a new car, do You prefer a "green" antiblocking brakes system,
> > or the "old" one?
> >
> > With kind regards,
> >
> >         Hans Juergen Bauer
> >         Industrial Engineering
> >         Passive Components
> >         Qualification
> >
> >         ALCATEL Stuttgart
> >
> > Pondering some recent postings on this forum, I began questioning some
> > of the assertions that eliminating lead is feasible. Specifically, I
> > wondered about the current inability (or, at least, lack of rating) of
> > many parts to survive temperatures in the 260°C range (many larger
> > ceramic capacitors, for example, are not warranted to survive immersion
> > in solder above approximately 230°C for even a few seconds). If lead is
> > removed from solder, the components will be required to survive at 260°C
> > or higher for quite a large number of seconds.
> >
> > If the components can be made to tolerate higher temperatures without
> > degradation when new solder(s) with higher melting temperature(s) are
> > introduced, why haven't component manufacturers already made their
> > devices more robust?
> >
> > Jim Smith
> > Managing Director
> > Cambridge Management Sciences, Inc.
> > 4285 45th St. S.
> > St. Petersburg, FL 33711-4431
> > Tel: (727)866-6502 ext. 21
> > Fax: (727)867-7890
> > eMail: [log in to unmask]
> >
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