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electrically conductive adhesives


Rob

#32826

electrically conductive adhesives | 23 February, 2005

Hi,

Does anyone have any experience of using electrically conductive adhesives, including info on the following?

1) Autodispensing/screen printing 2) Curing temps/profiles 3) Quality/conductivity of joint 4) Product recommendations

Our customer wants to use it instead of solder paste on some LED's - is this viable?

Cheers,

Rob.

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Indy

#32828

electrically conductive adhesives | 23 February, 2005

Hi Rob, I had tried printig anisotropic conductive adhesive as a replacement for solder paste. Following were my finding.

Adv: - curing temp is around 120-150C as compared to 217C (Pb-free) solder. - good electrical conductivity, since it is usually filled with silver particles. - not much cleaning is required coz no flux is used.

Dis Adv: - recommended printing by supplier was 8 inch/sec. I thought it was too fast. Though when I tried it at that speed it gave good deposition. - I did see lot of briding and slump at all print speed. Low or high.

you might want to have a look at this site too..

http://www.electronicsweekly.com/Article7412.htm

Cheers Indy

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Rob

#32852

electrically conductive adhesives | 24 February, 2005

Hi Indy,

Thanks very much for the info - very helpful. Was there any particular adhesive that stood out?

Cheers,

Rob.

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#32853

electrically conductive adhesives | 24 February, 2005

We have done some work with conductive adhesives. The main lesson is: They do not adhere well to solder. * For components, a silver-palladium or gold end termination is recommended. * For substrates, gold over nickel should work well.

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Rob

#32856

electrically conductive adhesives | 24 February, 2005

Thanks Dave,

From what I remember a lot of components went away from Silver Palladium to "base metal" terminations because of the difficulties in continuation of supply & stability of price. (Something about being mined in Chechnia or the Congo?)

We were planning on immersion Silver for the board finish - hopefully that should bond well with the Silver particles in the adhesive. (A lot of PCB houses over here appear to be standardizing on this finish to replace HASL due to the ROHS regulations). Substrate is Aluminium.

Cheers,

Rob.

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#32868

electrically conductive adhesives | 24 February, 2005

Rob: Why aren't the board houses over there going to lead-free HASL [not that HASL is the most wonderful thing on the planet]?

What's the price delta on an unit basis for a x-HASL, now imm Ag board?

Anyhow back to the point, so, you're proposing to: * Paste, reflow, maybe clean the pads where this LED would attach. * Mix a pot of epoxy and dab some on the LED pads. * Mount and fixture the LED. * Cure the epoxy.

If that's the case, we don't see this epoxy stuff conducting well, returning to our earlier point in this thread.

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Rob

#32918

electrically conductive adhesives | 28 February, 2005

Hi Dave,

Was planning on skipping the paste step & screen printing the adhesive straight onto the pad, then placing the component into the glue & curing. (Board has LEDs only)

Regarding the lead-free HASL issue - not entirely sure on the board manufacturers part, but we've always had far better results with Au, & even better with Ag - especially on fine pitch & BGA's. Price difference between Silver & HASL is about 3 or 4% from memory.

Thanks for your help,

Rob.

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#32920

electrically conductive adhesives | 28 February, 2005

You'll be able to tell pretty soon if this will work. * Our bet is the epoxy will corrode the silver. * Another concern is that you're not fusing the silver to the copper.

Why not ask the imm silver suppliers: * Alpha Level Silver [ http://www.alphametals.com ] * Mac Dermid Sterling [ http://www.macprintedcircuits.com/final ] * Uyemura International Corp [ http://www.uyemura.com ] Presa RGA-14

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Rob

#33003

electrically conductive adhesives | 2 March, 2005

Hi Dave,

Thanks for the info, it will be helpful. Planning on trying it on a number of finishes, and have arranged for some samples of the adhesive - Loctite 3880 to start with.

Have discovered something important already though - why not many people use it - a small matter of approx. $170 for a 30ml tube!!!!!!!

Cheers,

Rob.

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