Z-axis Thermal Expansion of FR4

[spartangirl]

I have found a value of 4.5% CTE(Coefficient of Thermal Expansion) in the z-axis for FR4. How do I use this to figure out what the change in length would be of a PCB over a tempertaure range?

Any help would be greatly appreciated.

 

[IRstuff]

You don't. You need to get the Cte for the in-plane expansion. The material has different properties in that direction.

TTFN

 

[spartangirl]

IRstuff,

It is in the thickness of the board that I am concerned about. Does that CTE make sense for this direction?

Thanks!

 

[47gandalf]

So are you trying to find out what the change in THICKNESS will be for this board over a temperature range?

If so, your data indicates a thermal coefficient of expansion of 0.045 inches per inch per degree Celsius (assumed temperature scale as you didn't state), or 0.045 millimeters per millimeter per degree Celsius.

Those would be changes from the thickness dimension at a known temperature, presumably room temp, or about 25 C, as specified by the board fabricator. So a negative change with cold (decrease in temperature) and a positive increase in thickness with a rise in temperature.

Does that help?