Having some issues with assemblies, I try to explain my question with some introduction.
Let's say, there's an assembly with two parts. Copper (OF / K30) and FR4. The copper part is milled from all sides extensively.
In the process both parts are mated at several points with bolts.
Later in the process the mated assembly undergoes a baking process for 48h 24h and 80°C.
We notice some deviations, the FR4 parts are dislocated along the mating plane. Those deviations might point to strong forces during the process steps between fastening of the bolts and final checks after the baking process.
K30 having a CTE of 17.7 ppm/K is not that far from FR4 (14-17 ppm/K). For my question I make the following assumptions:
- baking temperature has not crossed Tg of FR4 by accident, where CTE is known to change drastically
- alloy and FR4-type have not been exchanged accidentally
- fastening of the bolts have been performed properly and the parameters haven't changed
What process changes during manufacturing of the copper part can lead to a displacement of the mated parts during the heat treatment?
update The baking process itself is under heavy scrutiny on itself. So of course I'm interested in everything what can happen during that step as well. However my question aims on everything what can happen to the copper part before assembling it with the rest.
