I have fired this very challenging and hard-to-get-answer question before, but as I'm not much wiser I do it again. If anyone has the e-mail adress to James E. Morris at Binghamton, I would be glad to have it, lost it a year ago.

Now, as all know the conductivity of e.g. silverepoxy changes little around certain fill factor, let's say 70%, but below that, a dramatic change will occur, exp change and finally abrubtion in the electrical joint. At microwave freq the skin dept in silverepox and in a homogenous conductor are dissimilar, therefore, a good thumb rule is to make the silverepoxy conductor sq root of 10 thicker than the metal dito. The cause is the ratio of Ag-metal/Ag-organic, being approx. 10. A TechNet guy named Richard somwhere in the US used to apply similar  'home made'  formulas, but I have lost his identity, maybe he will see this mail and respond once more.

In RF circuits, good ground (current return) is vital for many applications where RF chips are used up to 70 GHz. If you solder the chips, there use to be no trouble, but epoxying, that's something else. Mike Joyce, Carey and many fellows know a lot of the conducting mechanisms in such matrixes, maybe I can get some pearls from them also. This was the background to my question that follows:

Anyone with praxis from silverepoxying large chip mounting and multiGHz applications? Do you have appointments on the  AC conductivity vs, inherent curing, fill factor, geometry and suppliers in the game? What are your requirements on voids and wetting percentage, meniscus and other possible factors that have paramount impact on said RF parameter (current return). Father Gilleo couldn't give very good answers, so I see one is in the few-mans-land.

If you think this topic is too far from PWB and like TechNet things, maybe I can get a knock on the door offline?

Said

Ingemar Hernefjord
Ericsson Microwave Systems

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