Feb 10: Jim, Mark and James.
Interesting. We do some similar practice just now, but we use 33-100um
aluminium wire. One end on thickfilm MCM gold pads, the other on FR-4
gold pads. From the litterature I saw that purple plague (and the other
intermetallics) won't grow considerably until over +170 Celcius
(Arrhenius was there, of course). The advantage with aluminumwire is
that you need no preheat, it's strong and it's a little bit cheaper,
maybe. But in principal, we would like goldwire better. The chain
gold-gold-gold must of course be safer than gold-aluminium-gold. I will
save your mails, and if I see any 'plagues' I will try to remember you
and tell you about our experience.

Guys like Werner Engelmaier must be groaning, all this was known decades
ago, don't we learn anything?  I represent such a
never-learning-company. Good for the consultants, isn't it (wha-wha).

                               Have a nice day // Ingemar
                               Ericsson Microwave Systems
                                  Sweden / now -40 Celcius

-----------------------------------------------------------------------

> Jim
>
> It is possible to pre heat the bond surface to 120 degrees C and
increase
> the ultrasonic energy to achieve a good bond >20g on pull test.
>
> ===== Original Message from [log in to unmask] (TechNet E-Mail Forum.) at
> 11/02/99 15:30
> >We have a need to connect a rigid flex pc board to a very small
optical
> >module.  We are in the prototype process now, on our way to an
> >instrument that will fly in space.
> >
> >We would like to wire bond using gold wire.  We are now to understand
> >the bonded surface needs to be pre-heated to 145 degrees C!!. That
may
> >not be suitable for an assembled PC board.  Aluminum wedge wire on
gold
> >pads seems be prone to "purple plague".  This will be a very short
run
> >(2 protos, 20 flight units) so we are far more interested in quality
> >than efficiency. This is not like connecting substrates to output
pins.
> >The module is 2.5" by 2.5".  We will be bonding through slots 1.5"
long
> >by .220" wide to a surface .062" below.  The bond pad size is .006"
by
> >.015".  When the two modules are together they are about a 2.5"cube.
> >Is there anyone that can provide some information gained from
experience
> >or else where that may help make this a success?
> >Thank you for your input.
> >
> >Jim Payne, Sandia National Labs [log in to unmask]
> >
> >
> >James R. Payne    MTS
> >MS 0967      Dept. 5706
> >Sandia National Labs
> >PO Box 5800
> >Albuquerque,  NM   87185
> >
> >Phone:  (505) 844-3336
> >FAX:     (505) 844-5993
> >email:   [log in to unmask]
> >
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