Bruce/Josep,
It as been a few years since the situation arose. It was related to the
development of a new high temperature, power bybrid concept. We found quite
vividly that 10 mil aluminum wires on copper in a non-oxidizing environment
(hermetic = nitrogen inside) degraded significantly after only a few hundred
hours of aging, whereas the 'control', baked in air, actually got better. I
forget the actual mechanism, but the results made sense at the time. I know
that on the surface, it does seem counter-intuitive, but that is the way it
worked out.
We ended up with the new packaging concept + plus conventional nickel & gold
flash platings, and all was (very) well.
That is about all I can say on the subject.
At 11:07 AM 3/5/01 -0600, you wrote:
>Josep,
>
>Steve does make a point. I did not address heavy Al wire bonding since you
>did not make reference to it, however, I do not see what advantage oxygen
>and moisture in a non-nitrogen, non-hermetic environment would bring to the
>table as Steve suggests... perhaps he will enlighten us both.
>
>Regards,
>Bruce
>
>> ----------
>> From: Creswick[SMTP:[log in to unmask]]
>> Reply To: TechNet E-Mail Forum.;Creswick
>> Sent: Monday, March 05, 2001 11:25 AM
>> To: [log in to unmask]
>> Subject: Re: [TN] Al wire bonding
>>
>> Josep,
>>
>> You did not define two critial parameters - wire size, and how many you
>> plan
>> to do!
>>
>> I beg to differ with Bruce's response a bit.
>>
>> Fine wire aluminum wire on clean copper does work, although I much prefer
>> the nickel plating too!
>>
>> Fine wire aluminum (1.25 - 2 mil) IS challenging! Normal Al wire doesn't
>> work very consistently - it is too soft. One obtains too much bond
>> deformation before a 'real' bond is formed. The trick is to use 'harder'
>> wire (lower elongation), but then the problem shifts to problems of
>> damaging
>> the IC's bond pads. If you are not very experienced at wire bonding, this
>> could be daunting!
>>
>> Specificially, heavy aluminum (5-10 mil diameter) works REALLY WELL on
>> copper - its only 'fault' is that it must be operated in an non-nitrogen
>> (ie. non-hermetic) environment to retain good pull strengths.
>>
>> Conclusions: If you have a couple parts to do, you might struggle though
>> as
>> suggested above. If you have large numbers of parts to do, make it easier
>> on yourself (as Bruce suggests) and get them plated! (But I suggest that
>> you test some sample plated parts before you plate up everything)
>>
>> PS - In many respects, automatic wire bonding is still an 'art', although
>> science helps out at times.
>>
>> And I can honestly say that the views expressed above are NOT those of my
>> employer.
>>
>>
>> Steven Creswick
>>
>>
>>
>>
>>
>> At 01:41 PM 3/5/01 +0100, you wrote:
>> >I'm unable to make a wire ultrasonic bonding (wedge bond) with Al wire
>> >directly to cupper pad.
>> >With your permission, I'd be interested to known if this bonding is
>> possible
>> >
>> >Thanks in advanced
>> >
>> >
>> >Josep M. Badia
>> >Servei de Recursos Tècnics
>> >Tèlf/Fax: 977 559630/559605
>> >Univ. Rovira i Virgili
>> >
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