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 Late 80s and even 90s papers would be outdated as materials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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