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Subject:
From:
Yuan-chia Joyce Koo <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Yuan-chia Joyce Koo <[log in to unmask]>
Date:
Fri, 29 Apr 2016 18:06:20 -0400
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text/plain (284 lines)
agree, pad printing might be better for small feature.
   jk
On Apr 29, 2016, at 2:24 PM, Mike Fenner wrote:

> Generally speaking out of the pot adhesives are easier to apply  
> than T3 -T4
> powder size solder pastes in terms of rheology and so on, essentially
> because the particle size of the filler is much smaller, and the  
> chemistry
> is more ink like. This is not counting the open time restraints of  
> course. I
> think I would be looking hard at alternatives to squeegee printing.  
> [Multi
> dot/bed of nails] transfer printing would be slight less wasteful  
> and easier
> to maintain a consistent process. Dispensing is good. 36-2 was top  
> material
> in its day, but later materials are now much better and I would  
> expect them
> to be more production friendly.
>
> -- 
> Regards
>
> Mike
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Ioan Tempea
> Sent: Friday, April 29, 2016 6:33 PM
> To: [log in to unmask]
> Subject: Re: [TN] Stencil printing of conductive epoxy
>
> Thanks Steve,
>
> Good points, pretty much in line with what I was anticipating.
>
> Best regards,
>
> Ioan
>
> -----Message d'origine-----
> De : Steven Creswick [mailto:[log in to unmask]]
> Envoyé : Friday, April 29, 2016 1:28 PM
> À : 'TechNet E-Mail Forum'; Ioan Tempea
> Objet : RE: [TN] Stencil printing of conductive epoxy
>
> Ioan,
>
> Please consider that my experience comes from a hybrid  
> microelectronics
> background and not from an SMT perspective, and in-general, we did not
> attempt to print/stencil less than a 10 mil feature size.  You are  
> in a
> different ballpark altogether at 4 mil.  Using solder and (scary) flux
> within a hermetic enclosure was akin to committing a sin because of  
> the
> ionics brought to the party.  That's not to say that power hybrids  
> didn't
> use solder, but we tended to use reducing atmospheres and fluxless
> approaches.
>
> I was thinking of the old Ablebond 36-2 (which is no longer  
> available).  Its
> minimum advertised cure temp was in the 130-150°C range, but yes,  
> we kept it
> in the 160-165°C range.  It was a great material, but was ionically  
> too
> 'dirty' to meet the TM 5011 requirements.
>
> The material properties of the material squeegeed onto the  
> substrate will
> change as well.  First things I can recall are tack and 'wetting'
> characteristics.
>
> My experience with low temp cure materials was there marked lack of  
> thermal
> stability, so in most applications requiring 125-165°C operational  
> life, we
> just couldn't use them.  Even for automotive (80°C) applications we  
> stuck
> with our higher temp favorites.
>
> Dispensing would result in less exposed air-time, but would definitely
> present issues of its own.
>
> Could you use a low temp solder alloy like Bi or In?
>
> I find it very hard to come up with a concise answer to your last  
> question.
> I remember stenciling 8-10 mil dots for Read/Write head e-blocks  
> back in the
> day, but we also found ways to dispense it quicker.  Adhesive would  
> have
> been a piece of cake!  My gut reaction is to say that the adhesive  
> will
> generally always be easier because one does not have the potential for
> solids/flux segregation, and the adhesive is 'more homogeneous' and  
> not a
> bunch of balls suspended in viscous medium (it's just much much  
> smaller
> flakes and spheres suspended within an organic medium...   :-)  )   
> Does that
> align with your thoughts?
>
> Most adhesives, unless specifically developed with the intent of
> screen/stencil printing (I think that is the key parameter here),  
> just don't
> have the required open-time properties that most solder pastes  
> would have.
> Pitting an adhesive solely intended for screen printing against a  
> solder
> paste would be a much better match/comparison.  With some of the  
> new vehicle
> systems and carriers nowadays, I'm thinking it could be a  
> reasonable toss-up
> as to which is better.  I'm sure there are some techies that can  
> provide
> much better insight than I.
>
> Steve C
>
>
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Ioan Tempea
> Sent: Friday, April 29, 2016 12:44 PM
> To: [log in to unmask]
> Subject: Re: [TN] Stencil printing of conductive epoxy
>
> Thanks Steve,
>
> I've seen it coming!
>
> I have an interesting curing temperature constraint, need to stay  
> below 80
> C. Honestly, I haven't been able to find too many epoxies that  
> would comply.
> If the Ablestik you mention is the one I know, it normally requires  
> 2 hours@
> 160 C to properly cure.
> I guess it will cost a lot in terms of scrapped chemical, but the  
> only way I
> see is to lay the epoxy on the stencil, quickly print a certain  
> quantity of
> products and discard the epoxy on the stencil as soon as it loses its
> properties. Then clean the stencil and start over.
>
> Process wise, how did you find epoxy printing compared with solder?  
> Is it
> more consistent? The area ratio constraint for stencil apertures,  
> is it more
> relaxed when dealing with epoxies?
>
> Thanks,
>
> Ioan
>
> -----Message d'origine-----
> De : Steven Creswick [mailto:[log in to unmask]]
> Envoyé : Friday, April 29, 2016 12:22 PM À : 'TechNet E-Mail  
> Forum'; Ioan
> Tempea Objet : RE: [TN] Stencil printing of conductive epoxy
>
> Ioan,
>
> With only a 4 hour pot life, you won't have much screen life at all.
>
> As the adhesive gets wiped across the stencil, and large surfaces  
> of the
> adhesive get exposed to the air, its properties will change quickly.
>
>
> For example, I used to use a single part Ablestik material that had  
> a 7 day
> pot life!!  We only allowed its use on a stencil/screen printing  
> application
> for 8 hrs before we discarded it.  You could detect the rheological  
> changes,
> even then.
>
>
> If you need to attain and maintain that kind of print geometry, I  
> recommend
> you search for another adhesive with a much longer pot life...
>
> Alternatively, they do make some really small dispense needles, but  
> with the
> short pot life I still think you have a challenge in front of you
>
> Steve C
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Ioan Tempea
> Sent: Friday, April 29, 2016 9:29 AM
> To: [log in to unmask]
> Subject: [TN] Stencil printing of conductive epoxy
>
> Dear Technos,
>
> I need to stencil print 4 mil in diameter, as thick as possible,  
> dots of the
> Epotek E4110-PFC, see
> http://www.epotek.com/site/administrator/components/com_products/ 
> assets/file
> s/Style_Uploads/E4110.pdf
>
> What is your experience with this material?
> Any suggestions regarding stencil design/squeegee material/printing  
> program
> parameters?
>
> Thanks,
>
> Ioan Tempea, P. Eng.
> Manufacturing Engineer, Satellite Systems
>
> [cid:[log in to unmask]]
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