> Hello
> My first post and first question to the experts.
> I am new to the electronic game most of my experience has been in mechanical
> inspection and test.
> My question: is there a rule of thumb on material shrinkage on board
> material or a spec. Our boards are coming in with all the dimensions at
> nominal but after wave they have shrunk down to the low limit and sometimes
> below low limit. Most of our tolerances are +/- .003.
> This is giving us headaches with interference problems when we put other
> components on the boards.
> Is it normal for the boards to shrink. Our arrays are approx. 4" x 12" with
> 25 separate boards on each array.
> Thx's in advance
> Tom Oliver
> Eagle Comtronics
> [log in to unmask]


Tom,

Wait a few days and measure them again. The reflow process will dry the boards
out making them shrink. Once back in the real world they'll re absorb moisture
 from the atmosphere and expand.

If you want a quick test, measure a board, process it, measure it, put it in a
bucket of water overnight and measure it again.

Regards,



Eric Christison

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