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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