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. 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