I worked as a glassblower for 17 years making electron tubes
and did a good amount of work with Kovar.

Kovar is wet by silver solders using flux or hydrogen brazing.
Regrettably, tt is also cracked by silver penetration of its
grain boundries. You can get away with silver brazes if you use
care. Cd/Si alloys are useable if vacuum compatability is not
an issue. It is better to use a silver utectic alloy such as "Cusil"
m.p. 780 C and minimize the "soak" time during brazing. Cusil has a
narrow solidus/liquidus range which helps minimize grain
penetration. RF induction is a reliable way to do this braze. You
should make a solder preform of wire (round cross section) or, if
you have a press, a flat washer.

If you have the thermal budget Cu/Au or Ni/Au eutectics are
preferred if high-vacuum integrity is a must.

Bob Hamilton

-
                        Bob Hamilton
                        Microlab Facilities Manager
                        University of California - Microlab
                        Rm 406 Cory Hall
                        Berkeley, CA 94720-1770
                        phone: 510 642-2716, fax: 510 642-2916
                        http://www-microlab.eecs.berkeley.edu:8080/

Micro Bond wrote:
>
> hi i am trying to find out what materials will wet well to kovar. my
> application is to bond kovar to tungsten carbide, so i have to find a thin
> film that will wet to both materials. i have found that Silvaloy ("High
> Silver" compositions) wet to WC around 600 - 700 C, but have no idea if it
> will also wet to kovar. do have any recommendations or advice for me? i
> appreciate all the help you can give. thanks.
>
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--

                        Bob Hamilton
                        Microlab Facilities Manager

                        University of California - Microlab
                        Rm 406 Cory Hall
                        Berkeley, CA 94720-1770
                        phone: 510 642-2716, fax: 510 642-2916
                        http://www-microlab.eecs.berkeley.edu:8080/