Ingemar
Good to hear you're out there. Unfortunately, I don't have any such paper.
The issue you bring up is basic metal-Si (Schottky barrier diode)
semiconductor physics...not a focus to most of those in the PWB world. You
can read about this in almost any solid-state physics book. Typical voltages
to overcome the barrier can be as high as 0.5-1.0V, although it depends on
the doping level and other related stuff. Silver epoxy can be a bit more
complicated because it forms a very thin sulfuric (I think, if not it's
oxide) coating (from reacting to air and the epoxy resin) that acts like an
insulator that get's broken down easily, but can affect the Schottky
interfacial properties. Under these situations, you have various values of
Schottky barriers (think of it as a distribution of resistor values with a
critical turn-on voltage). Because the metal-Si interface is dictated by
charge carrier density and that this density is exponential with both
temperature and doping, it gets very squirrelly (for you non-english
speaking folks..."weird").
There is also the situation where the Si is doped such that you form Ohmic
contacts (your standard contact resistance), which also has some variation
in values, but not as severe in affecting electronic current because the
charge density does not vary significantly.
In short, if you are looking into this, avoid non-wire bonded or metal
bumped Si devices. Look into IEEE journals in the mid-80's or look at
recent work in anisotropic conductive adhesives in flat panel displays
papers of the 90's. Call Hitachi Chemical (they are the big supplier) or 3M
(they have products out there and probably a lot of publications/patents)
for information on the adhesive electrical properties. Lastly, when I think
of RF, I track down contacts at Teradyne (think military).
Good luck
Carey
-----Original Message-----
From: Ingemar Hernefjord (EMW) <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Date: Monday, February 14, 2000 2:19 AM
Subject: [TN] GHz and filled adhesives
>Gidd Moerning all,
>I have something that may be too far from PWB, but I dare try: who knows
about noise in metal filled adhesive joints? Many years back people found
that the conducting mechanism in thin silver epoxy joints reminds of that in
semiconductors, i.e. you have something like a diode, but very small
forward current drops and hardly measureable reverse blocking, anyway, it
may cause noise. Unfortunately, I have lost the article and the guy who made
research in this issue (possibly IBM, Raytheon, HP... was american I'm
sure). Anyone out there with experience from this field and RF-noise?
>txs in advance
>Ingemar Hernefjord
>Ericsson Microwave Systems
>
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