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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