Paul,

I was addressing aging, or material oxidation over time, as both foil and resin degrade to a point
they no longer maintain effective bond. I sure agree you are right as hole wall plating is a big
part of another equation.

Epoxy material Tg's have increased (not to the point of polyimide or BT), but Z axis expansion rates
remain at about 40-60 ppm/degree C. for them all. If hole plating quality is not acceptable, failure
occurs during thermal stress/shock. This especially is true considering tensile and elongation, or
ductility variablities. With some new/old plating chemistries, ductility may be reduced but remain
acceptable for blind, buried, or micro vias (with numerically small aspect ratios), as examples.

Many board shops are able to manage processes to the extent 20-30% elongation (with 40,000 lbs.
tensile strength) is possible and often achieved - depending on chemistry. This works well for high
aspect ratio holes no matter the material type - except some Teflon types with very high expansion
rates. These and other obvious factors have been addressed many times on this forum, as you know,
such as various plating types, "throwing capabilities," current management, chemistries, etc..

And on it goes,

Earl Moon

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