Thanks all
found lots of info a MatWeb
Guy,  the Hysol 3126 is one way conductivity
I got the Masterbond whitepaper and reviewing it ...


On Wed, May 1, 2013 at 9:16 AM, Watson, Howard A <[log in to unmask]> wrote:

> Eva,
>
> I was also researching conductive epoxies and found a paper here:
> http://www.masterbond.com/whitepaper/electrically-conductive-adhesives
> I had to register to access it. I don't endorse this company in any way,
> but maybe this paper will help you in some way.
>
> Good luck!
>
> Howard A. Watson
>
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Eva J
> Sent: Tuesday, April 30, 2013 4:20 PM
> To: [log in to unmask]
> Subject: Re: [TN] Conductive epoxy to install SMT parts
>
> Thank you very much
>
> Indeed it is a difficult situation with limited solutions for our specific
> application.
>
> Onward TechNet Soldiers!
> Eva J
>
>
> On Tue, Apr 30, 2013 at 5:07 PM, Mike Fenner <[log in to unmask]> wrote:
>
> > Well the basic laws of physics and chemistry haven't changed. The
> > plethora of papers at that time does identify the issues very well and
> > explain what is needed. The reason for that burst of effort was that
> > Ag conductives - iso or anisotropic - were seen as a possible
> > alternative process in the light of the looming lead ban.
> > I was involved in such a project (at a somewhat low level technically,
> > more marketing orientated). Our conclusions were the same as most
> > others. First that at least three breakthroughs would be needed to
> > have anything like a drop in adhesive replacement for solder. Second
> > that the use of adhesive interconnects would continue to grow, but by
> > designing for adhesives not by designing an adhesive to be a solder.
> > The lead ban would just tilt the balance of choice slightly more away
> > from solders. We do still solder of course.
> > Overall the issues now are the same as then. They are better addressed
> > in newer products by a number of sequential incremental developments
> > in process and in in-service performance. Newer products can have snap
> > cure schedules which give comparable thermal exposure in processing,
> > maybe less. They can contain oxide reduction additives, and corrosion
> > inhibitors and so on to increase reliable conductive bond life and
> > maintain mechanical integrity.
> > Conductivity is still relatively poor. Thermoplastics do overcome one
> > of the biggest draw backs which is reparability but not without
> > performance costs.
> > So modern products can be closer to solders in service and may well be
> > good enough, but this is conditional on component surfaces being
> > optimised for bonding not soldering. Process parameters will also need
> > to be adjusted for the way the products behave. For example what you
> > print is what you get, so No self alignment and so on.
> > It may be that you could use a low temp soldering process, if not then
> > of course use adhesives, but do speak with suppliers to obtain optimum
> > product and process conditions. Keep in mind that each
> > adhesive/process will be application specific, so by and large you
> > can't just switch to an other suppliers functional equivalent as you
> > can with solders, you will need to revalidate.
> >
> >
> > Regards
> >
> > Mike Fenner
> > Bonding Services & Products
> > M: +44 [0] 7810 526 317
> > T: +44 [0] 1865 522 663
> > -----Original Message-----
> > From: TechNet [mailto:[log in to unmask]] On Behalf Of Eva J
> > Sent: Monday, April 29, 2013 1:59 PM
> > To: [log in to unmask]
> > Subject: Re: [TN] Conductive epoxy to install SMT parts
> >
> > Conductive epoxy is being considered as an electrical and mechanical
> > bond since the component can not withstand reflow temperatures. The
> > future application will be an ENIG finish on PCB with gold finish on
> > the component termination. Late 80s and even 90s papers would be
> > outdated as materials have changed. So no one is aware of recent
> > papers regarding conductive epoxy?
> >
> > Thanks
> > Eva
> >
> >
> > On Sun, Apr 28, 2013 at 7:41 PM, Mike Fenner <[log in to unmask]> wrote:
> >
> > > It's not totally clear why you want to adhesive bond instead of solder.
> > Are
> > > you looking to adhesive bond special devices to otherwise assembled
> > boards?
> > > There maybe ways to solder using repair techniques for example.
> > > If you wish to use adhesives you will need to consider conditions of
> > > use, service life, and in production surfaces to be bonded as well
> > > as max process temp and time. These will be different from solders.
> > > Generally adhesive bonds are not as strong as solder, and in
> > > non-hermetically sealed
> > packages
> > > service life can be shorter (but maybe sufficient in either case).
> > > As already said epoxies do not bond well to tin or tin based alloys.
> > > Gold is also a low energy surface and will give low bond strengths
> > > with
> > adhesives.
> > > So bond strength could be an issue, this is in addition to any
> > > problems that might arise from the Ag:Sn interface. Some suppliers
> > > do claim to have addressed the long term conductivity issues.
> > > Do keep in mind that whereas adhesives can be classified into
> > > generic types, (epoxies, silicones, acrylates etc) they are all
> > > supplier unique within that classification. This means you will need
> > > to check or verify product performance claims with every supplier.
> > > [This is not like solder pastes where although flux chemistry may be
> > > supplier specific, a solder alloy
> > such
> > > as Sn63 is not.]
> > > You will need to observe the cure schedules in the supplier data
> > > sheets, treating them as minimum times/temps at the bond line or the
> > > product will not develop data sheet properties.
> > >
> > > Regards
> > >
> > > Mike
> > >
> > >
> > > -----Original Message-----
> > > From: TechNet [mailto:[log in to unmask]] On Behalf Of Steven Creswick
> > > Sent: Thursday, April 25, 2013 3:31 PM
> > > To: [log in to unmask]
> > > Subject: Re: [TN] Conductive epoxy to install SMT parts
> > >
> > > Eva,
> > >
> > > You should ask the formulator for this information.  Really attempt
> > > to
> > nail
> > > them down and get them to provide real, and detailed data - one real
> > > live part types.
> > >
> > > In general, it is quite difficult to get most adhesives to adhere to
> > > the diverse surfaces finishes presented in SMD work, at temperatures
> > > that the SMD assembler [and components] will tolerate.  Making it
> > > more flexible is only one factor to consider.
> > >
> > > Mechanical, thermal, or other environmental stresses typically
> > > quickly
> > show
> > > the weak links.
> > >
> > >
> > > Side note - if "cured" over the weekend, I suspect that it is more
> > > of a humidity cure RTV than an "epoxy" based system.  Do you smell
> > > acetic acid [vinegar] during cure?  = bad idea.  Or do you smell more
> of an alcohol?
> > =
> > > okay.  Silicones have a nasty way of tending to migrate to places
> > > you
> > don't
> > > really want them to go... switches, connectors,
> > >
> > > Can your production live with a 48-72 hr cure?
> > >
> > > I would be sure to ask the formulator whether the material has an
> > > epoxy backbone, or a silicone backbone so that I could get a better
> > > grasp of
> > its
> > > mechanical properties.  I am assuming that if it is a silicone,
> > > under normal conditions, it will already be above its Tg, and
> > > therefore already in it 'high expansion' state.  I also make the
> > > generalization that it will
> > remain
> > > flexible until down in the -20 to 0°C range [subject to the
> > > specifics of the material]
> > >
> > > Steve C
> > >
> > > -----Original Message-----
> > > From: TechNet [mailto:[log in to unmask]] On Behalf Of Eva J
> > > Sent: Thursday, April 25, 2013 10:01 AM
> > > To: [log in to unmask]
> > > Subject: [TN] Conductive epoxy to install SMT parts
> > >
> > > I am looking for guidance on conductive epoxy selection for
> > > components on PCBs. I heard that there is a formulation of
> > > conductive epoxy with
> > silicone
> > > as a filler that is more flexible. Do you know of any studies or
> > > evaluations available on conductive epoxy for electronics?
> > >
> > > We attached a 4 pin LGA component that has gold finish terminations
> > > to a HSAL finished PCB. We syringe dispensed the conductive epoxy to
> > > the land pattern. Optically machine placed part and allowed the
> > > conductive epoxy
> > to
> > > cure over the weekend.
> > > During environmental stress test ( hot / cold cycling) one joint
> failed.
> > > All of the LGAs were removed and what we found is the component came
> > > off way to easily.
> > >
> > > I would like to continue using conductive epoxy to mount special
> > > application
> > > SMD's: however reliability is a concern. Any words of wisdom?
> > >
> > >
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