FR4 CTE vs Steel screw/nut CTE

[dmsang]

New to the forum . . .
I am wondering how a .093 thk FR4 board Z direction CTE would compare to a steel screw CTE.

The issue is that there is a heatsink bolted to a .093 FR4 board using a steel shoulder screw and nut.

Any ideas what the CTE mismatch between the bolted joint and FR4 Z direction might be (per C) ?

THanks !

 

[felixc]

FR4 expands more than metal for sure. I always use starlocks or loctite when I screw heatsinks on boards.

 

[itsmoked]

I have never seen anyone care about it.. I never have and have had no problems even with .125 boards. Feeling seems to be that the FR4 will deform(flow) sooner-than-later relieving the compression stresses. Most do use starwashers though as mentioned by felixc.