Hi Thad,

Z-axis expansion is probably going to be an issue with this board unless
you use a material with Tg>170 deg.  You can also do some things with the
plating to provide the best tensile/elongation strength possible. (Panel
plating, lower amperage, etc.) but the Z-axis expansion is the critical
factor here.

Have a good day,

Sharon

At 05:39 PM 1/30/98 CST, you wrote:
>     Currently we are designing a board thicker than normal with small
>     holes.
>
>     The board is a 10 layer board, 082" thick, and uses 13.5 mil
>     drilled/plated holes.
>
>     The board is large ~ 13 x 16" in size.  It is HASL.  During component
>     assembly it will see 2 IR processes and a  wave.  We are specifying
>     the board as IPC Class 2.  It will be used in high end computer
>     product.  Reliability is very important.
>
>     In light of the above I have several questions for this distinguished
>     group:
>
>     1.  Considering the 6 to 1 aspect ratio, using conventional FR-4 will
>     the design above have reliable plated through holes?
>
>     2.  We are considering specifying that the FR-4 be of Tg greater than
>     170 Deg C.  The hope is that this will improve hole relaibility.  The
>     problem is that this will add significant cost to the board.  Is it
>     necessary to do this?
>
>     3.  The design is dense so that we cannot grow the hole significantly.
>     We are considering permitting hole breakout of 1 mil, so that the
>     holes can be drilled larger.  Is this a reliability risk?
>
>     4.  Are there other alternatives (not so expensive) to improve hole
>     reliability?
>
>     I would appreciate any feedback.
>
>     Thanks,
>
>     [log in to unmask]
>
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