>We are attempting to attach a nickel-plated copper heatsink to a 10
>layer PWB per a set of manufacturing drawings that only states that "the
>heatsink shall be attached with prepreg".  It does not call out a
>pressure, temperature, cycle time, or a type of prepreg.  We have
>assumed that we would need a "low-flow" type of prepreg.  We have tried
>some sample cards with a low-flow prepreg (PC-GF 108V by Westinghouse
>Fortin) that we have on hand;  we have had good registration of the
>heatsink to card, but the adhesion has not been as good as we would have
>liked, and the heatsink seems to have been pressed "into" the board (you
>can feel the outline of the heatsink on the backside of the card).  We
>ran the press at the lowest possible pressure we can for our press (15
>lbs).

>We are looking for suggestions from anyone who has experience with
>laminating heatsinks to PWBs.

Sounds like too low a pressure for that noflow. The noflow goes bad a little
quicker than normal prepreg too. If you can do vacuum try 75 psi with fresh
noflow; cool in the press. What is the heatsink thickness?


Tom Waznis

Hallmark Circuits Inc., Lam Eng.

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