James and Roger,

Unfortunately there are few options for Pb-free which will survive a reflow at 260C.  As James listed there are the high Au alloys which work very well, but are expensive.  Roger has listed brazing alloys., but they have rather high melting temperatures.  Sumitomo Metals and Mining published a paper on a Al-Zn-Mg-Ga alloy for die attach which melts around 340C, but they stated it was difficult to work with.  Sn8.5Sb and slightly higher Sb have a 236C solidus so they may work for some applications, but will not survive 260C.  

The good news might be that applications where a solder that melts above 260C such as capacitors and die attach may be allowed to remain Pb containing until viable alternatives are developed.  Note that I said viable and not fully tested and no added cost alternatives.  I believe that all of the alloys above can be ruled out as non-viable at this time.  However, it is my belief that the SMM alloy or something similar will be developed shortly that will permit replacement of the high-Pb alloys at acceptable cost to those driving the elimination of Pb (i.e. 2 to 3 times the cost of the current high Pb-alloys).  I do not want to start a debate regarding if this is an acceptable cost since the answer depends upon your point of view and the technical/user viewpoint will lose to the environmental/political viewpoint if the cost is even close (less than 2X to 3X is my estimate of "close").

I am more than willing to serve as a central point of contact on these higher melting solders since it is critical to my company (we sell a fair amount of die attach solder and polymer) and most of the focus of this forum is on the replacements for Sn37Pb and related alloys.

Regards - Marty

Martin (Marty) Weiser, Ph.D.
Product Manager - Plated & Discrete Products
AlliedSignal Electronic Materials (formerly Johnson Matthey Electronics)
Spokane, WA
(509) 252-2757 (phone)
(509) 252-8617 (fax)
[log in to unmask]

>>> Roger Bilham <[log in to unmask]> 11/12/99 09:45AM >>>
In message <[log in to unmask]>, James
Canner <[log in to unmask]> writes
>We are really at a loss to decide how to attach leads to ceramic capacitors
>for use with no lead solders such Sn-Ag-Cu for this reason.  There is no
>suitable higher melting point solder that we can find.  Are there any
>suggestions?  We currently can use 90Pb/10 Sn alloy, but lead free choice
>seems to have over 20 % Gold.

James,

This is one of (at least) two areas where a higher melting point lead-
free solder is needed, the other being bump attachment of chips inside
IC packages. Are there others?

If you can stand the temperature, you might consider a Cu-Sn-Ni-P alloy
melting at about 600C (1100F) with a 10C melting range. It is available
as paste or solid.

If this is too hot you might find that a zinc based alloy would work.
This, though, would probably need a fairly agressive flux, which you
might not like.

--
Roger Bilham
Roger Bilham Consultancy
Tel: 0181 467 8819
Fax: 08700 548 613

################################################################
Leadfree E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c
################################################################
To subscribe/unsubscribe, send a message to [log in to unmask]
with following text in the body:
To subscribe:   SUBSCRIBE Leadfree <your full name>
To unsubscribe:   SIGNOFF Leadfree
################################################################
IPCWorks -October 25-28 featuring an International Summit on Lead-Free Electronic
Assemblies.
Please visit IPC's Center for Lead-Free Electronics Assembly
(http://www.leadfree.org ) for additional information.
For technical support contact Gayatri Sardeshpande [log in to unmask] or 847-790-5365.
################################################################