It's a while since I followed Ag glasses, [they had only a narrow
application]. I recall they got as low as 220-230c claimed, but recall also
some reported loss of properties.
Mike
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steven Creswick
Sent: Tuesday, June 04, 2013 12:19 PM
To: [log in to unmask]
Subject: Re: [TN] Conductive epoxy to install SMT parts
Mike,
I seem to recall that many of the 'cure'/sintering temperatures for the Ag
glasses were in the 250-310°C, at their lowest. Were developments made that
allowed them to come down below that?
Steve C
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Mike Fenner
Sent: Tuesday, June 04, 2013 6:45 AM
To: [log in to unmask]
Subject: Re: [TN] Conductive epoxy to install SMT parts
HI Inge
Attached is an old presentation (early 1990's) on conductive adhesives,
which you might like to add to your Dropbox archive. Technically it has
stood up remarkably well, so is still a good primer for solder engineers. I
apologise though for its garish appearance.
Silver glasses seem to have fallen from the mainstream (together with
ceramic packages and so on). Sod's Law now says someone more informed will
say opposite.
They were a seemingly obvious candidate to revisit as a Pb-free, Au-free
alternative to high Pb content die attach solders, but were set aside again
as the glass component could not be made lead free.
Best Wishes
Mike
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Inge Hernefjord
Sent: Monday, June 03, 2013 10:26 PM
To: [log in to unmask]
Subject: Re: [TN] Conductive epoxy to install SMT parts
.........................................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..............................."
I learned that the hard way by much embarrassment and pain....
Q: is Silver glass discussed and reviewed? I used that in a Space
application for its low outgassing and resistance against high operation
temp as well as high electric conductivity
Inge
On 1 May 2013 15:16, 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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