I sent this to the wrong address - apologies. What laminate are you using? I have some data on the Z-axis expansion of several common laminate material. My company was recommended to go with the following speicfication for FR-4 on a Flight compatible piece of hardware: Use HTE (ehich is class 3) copper foil for conductive layers, 1.5 micron PTH wall thickness of copper with 12-30% elongation, 45k-55k PSI tensile strength. Some also specify a Nickel coating on the PTH barrels after copper plating for strength although we were assured that this was not necessary. This is a common specification in the aerospace industry where the product experiences large and frequent temperature cycles. The above spec was developed for a new laminate material called Non-Woven Aramid. Martin Kennett - Design Engineer, SED Systems Inc, Saskatoon, Canada. [log in to unmask]