Hi Steve,

That's a large size question!!  First, a mechanical engineer is going to have
to determine how stiff is stiff, related to your board.  This all depends on
the board size, weight distribution and intended performance environment
(vibration, shock, etc.)

One of the important items during board layout is to locate the heavier
components adjacent to card guides or unit housing structure.

Some of the options open to you include:
1] using a bonding material which is compliant and allows the board and
stiffener to expand at different rates with only minimum distortion;
2] using a stiffener material which closely matches the TCE of your board, or
visa versa;
3] adding a stiffening core;
4] using stiffeners which are mechanically attached, without adhesives;
5] thickening the board laminate structure.

Be cautious of adding stiffeners and cores which add to the thermal mass of
the board and have an adverse affect on your soldering processes.  Also be
cautious of thickening the basic board - Z axis expansion of some of the lower
Tg laminates can result in separated pads.

I can be reached at 256.882.4536, if necessary.

Regards - Kelly

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