Ingmar,
I've been wire bonding for 22 years to literally 100's of different products
and to everything including GaAs devices up to 96 GHz. Au Themocompression
(heat and pressure) wedge bonding is typically recommended for GaAs due to
brittle nature of material with concerns to ultrasonically induced cracks
and smaller loops for better Microwave performance with wedge bonding. It
is typically not related to EFO induced voltages in the device. With
countless Failure Analysis efforts I have never seen a confirmed failure of
EFO induced voltages but it is, of course, extremely difficult to confirm
and is rarely looked at.
By the way, you can very successfully bond GaAs with thermosonic (heat and
ultrasonic) ball bonding, however, efforts should be utilized to minimize
the amount of ultrasonics through higher temperatures and/or longer bond
times, especially with a 25 micron ball. Finally, Au Wedgebonding can be
reverse bonded with 1st bond on the substrate and 2nd bond on the device but
is usually easier to accomplish with 1st bond on the device, typically due
to targeting concerns (but that tail can be a pain at times). Forgive me,
You probably know most of this already but I included it for the benefit of
our friends in Technet.
Regards,
Bruce Misner
> ----------
> From: Ingemar Hernefjord
> (EMW)[SMTP:[log in to unmask]]
> Reply To: TechNet E-Mail Forum.;Ingemar Hernefjord (EMW)
> Sent: Wednesday, June 07, 2000 4:56 AM
> To: [log in to unmask]
> Subject: Re: [TN] wirebonding EFO
>
> -----Original Message-----
> From: Ingemar Hernefjord (EMW)
> Sent: den 7 juni 2000 10:10
> To: 'Creswick'; TechNet E-Mail Forum.
> Subject: RE: [TN] wirebonding EFO
>
>
> Thanx MCM bro Steve,
> we use Delvotec and K&S 25micron Au balls on GaAs MMICs. We had some ideas
> about cratering, bad silverepoxy joint under chip or EFO induction. My
> hypotalamus says cratering is most likely to cause hidden troubles,
> because GaAs 80um chips are fragile, others suspect the glue joint for not
> cooling enough, and finally there are some guys that believe more in the
> EFO hazardous model. Now, Watt do you feel for U/S ball bonding in
> principle yourself? Some chipmakers recommend thermosonic or wedgebonding
> and don't mention U/S, must be something behind that. The later method has
> more than one disadvantage, I think of placing 1st bond on top of chip and
> then 2nd down on conductor. Should be vice versa. Guess you buy MMICs
> from same suppliers as we do, not many in that club. Never got a warning
> from them concerning U/S ball bonding?
>
> I'll keep you informed
>
> Ingemar Hernefjord
> Ericsson Microwave Systems
>
> -----Original Message-----
> From: Creswick [mailto:[log in to unmask]]
> Sent: den 2 juni 2000 06:02
> To: TechNet E-Mail Forum.; Ingemar Hernefjord (EMW)
> Subject: Re: [TN] wirebonding EFO
>
>
> Ingemar,
>
> You raise an interesting point. Although I can not say we have duplicated
> your findings, it would be logical to expect the 'already made' wire bonds
> to act as miniature antennae.
>
> The good/bad news is that usually all the package leads are shorted
> together
> by tie bars, etc. at this point in the process, and the package and leads
> are firmly mechanically clamped into a thermally (and capacitively)
> massive
> heat stage - which is at ground potential.
>
> I might caution that possibly your scope probe either by physical location
> or size does not realistically represent a wire bond - one way or another.
>
> Many times we will bond the Vss & Vdd pads first. One could probably take
> both sides of the argument as to whether that really makes a difference in
> all cases.
>
> Keeping the EFO away from the work is ultimately limited by machine
> mechanics.
>
> Just think of all the ga-zillion IC's bonded in this manner in the last
> 15-20 years.
>
> Maybe we should go back to the ol' hydrogen gas flame-off. Can you imagine
> the bonding rate reduction that would make - and all the liability and
> safety issues that it would raise nowadays??
>
> Keep us posted.
>
> Steve Creswick - CTS
>
>
>
>
> At 12:50 PM 5/31/00 +0200, you wrote:
> >Anyone in the club who have heard if the flameoff can induce voltage in
> the
> material that you bond on?. E.g. we have checked with an osc probe and
> found
> peaks up to 50V when the flame goes off. Some semi chips without I/O
> guards
> seem to get dizzy. Anyone with experience?
> >Ingemar Hernefjord
> >Ericsson Microwave Systems
> >
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