Eric
In 15+ years of dealing with Ag epoxies I never saw true Ag migration, Saw
bleed reasonably often. Rarely with particles, but it can happen. All
epoxies can slump or bleed to give a resin rich shell/perimeter, albeit thin
and this is without significance.
Occasionally the adhesive or a component of the adhesive will bleed out on
an ultra clean surface, as say in quartz crystals - when this happens it can
give a conductive trail. Or at least a reduced resistance trail. This then
shorts, arcs or fails in some way and the fault post event is attributed to
silver migration. When I was involved suppliers had special no bleed
formulations usually suffixed(NB). These days things are likely different.
As I said "I hope a real epoxy person ....." :)
Regards
Mike
* Please think before you print
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Eric Christison
Sent: Wednesday, July 07, 2010 5:35 PM
To: [log in to unmask]
Subject: Re: [TN] Hybrid precap q
We use conductive epoxy in close proximity to bond wires, we're talking
the same kind of distance as you have.
We've never seen a problem and find it hard to picture silver particles
moving even if the epoxy did. I assume the epoxy is properly cured
before the lid is closed.
I'd do some testing all the same. Your glue may be different from ours.
Regards,
On 07/07/2010 17:18, Mike Fenner wrote:
> Hi Inge
> I hope there is a real conductive adhesive person who will answer this.
> In the conditions of use you describe I probably would be more concerned
> about bleed than silver migration at those geometries. If the stuff bleeds
> it could carry conductive particles to adjacent areas. It could then cure
in
> place or the bleed could be a component volatised off on cure.
> Either way you are left with a hard to detect lowered resistance path of
> silver fines. If the stuff cures without bleeding then I would think it
> reasonable to assume it is immobile for life of assembly.
>
> If the epoxy is truly wetting up the surfaces then it seems to be more
> mobile than normal, so increasing the concern for bleed form deposited
area.
> Normally these things cure and bond pretty well as placed.
>
> I think it is more likely there is too much adhesive. Either way it sounds
> advantageous to decrease it if possible. You only need to go say 1/3 up
chip
> sides to get an inspectable fillet. Excess adhesive would not increase
bond
> strength that much.
>
> As a consultant you can only offer your advise (in writing of course). If
> they reject it that's up to them. But of course later on, as a true
> consultant, you could then be well placed to earn another double whammy
fee
> for telling them how to fix the problem on assembled products...
> :)
>
>
> Regards
>
> Mike
>
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Inge
> Sent: Wednesday, July 07, 2010 11:16 AM
> To: [log in to unmask]
> Subject: [TN] Hybrid precap q
>
> Hi all,
> will be back with quiz 11, but before that , I have a q about silver epoxy
> mounting MMIC chips. The amount of glue is so rich, that the silver epoxy
> wets all the way up the walls and stops just before the horizontal plane
of
> the chip. Now, some conductors are as close to the chip edge as two times
> the diameter of a bond wire, which is about 50 um. I dislike such a small
> distance between the silver and the conductors. I'm doing a consulting
job
> for a company, and they mean that this space is enough. The chips are in
a
> laserwelded kovar package, so they are well protected, but I'm still not
> satisfied. I've seen too much of migration issues in my days. The
packages
> are class S. What are your opinions?
> Thanks in advance
> /Inge
>
> --------------------------------------------------
> From: "Whittaker, Dewey (EHCOE)"<[log in to unmask]>
> Sent: den 6 July 2010 17:43
> To:<[log in to unmask]>
> Subject: Re: [TN] NTC: Friday quiz 11
>
>
>> It's like what Doug said when he was asked if he could hear in a vacuum:
>> "is it turned on"?
>> Dewey
>>
>> -----Original Message-----
>> From: TechNet [mailto:[log in to unmask]] On Behalf Of Ken Bloomquist
>> Sent: Tuesday, July 06, 2010 8:18 AM
>> To: [log in to unmask]
>> Subject: Re: [TN] NTC: Friday quiz 11
>>
>> Did we ever find out what these were?
>>
>> -----Original Message-----
>> From: TechNet [mailto:[log in to unmask]] On Behalf Of Inge
>> Sent: Friday, July 02, 2010 10:40 AM
>> To: [log in to unmask]
>> Subject: Re: [TN] NTC: Friday quiz 11
>>
>> Hi Laides and Gentlemen,
>> time again for you to sharpen yourself after a whole week of sloppiness
>> and
>> lack of challenges. The real brainy solves both mysteries.
>> Steve, are you taking the catch? Twangggg.....
>> /Inge
>>
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--
Eric Christison
Consumer& Micro group
Imaging Division
STMicroelectronics (R&D) Ltd
33 Pinkhill
Edinburgh EH12 7BF
United Kingdom
Tel: +44 (0)131 336 6165
Fax: + 44 (0)131 336 6001
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