At 15:53 23/01/97 -0600, you wrote:
>
>We received this via fax at the IPC office and are forwarding to technet
>for comment. Can anyone help?
>
>Regards
>Dave Bergman, IPC
>
>Statement of Process Problem
>
>We are fabricating a 10 layer multilayer PWB with a 0.025" thick solid copper
>heatsink (12" x 18") in its center, with 5 layers on each side. This PWB has
>been previously fabricated using a conventional multilayer layup methodology
>with all layers assembled and then laminated in one package. We experienced a
>low yield rate. It was attributed to shorts caused by bubbles that formed
>within the drilled holes of the heatsink.
>
>We are currently experimenting with changing the production process to
>laminate the PWB in two stages - first completely fill the holes in the
>heatsink with prepreg, inspect and Second - layup the layers as usual. The
>heatsink undergoes pattern hole drilling, sanding and black oxide surface
>preparation treatment. The heatsink is assembled in the following package in
>the Multilayer Lamination Room: steel (12" x 18") lamination plate, aluminum
>sheet, 1 sheet tedlar release, 1 sheet each of 1080 prepreg, 2 sheets each of
>106 prepreg, heatsink, 2 sheets each of 106 prepreg, 1 sheet each of 1080
>prepreg, 1 sheet tedlar release, 1 aluminum sheet, steel lamination plate.
>The package undergoes lamination in a sealed vacuum "turkey" bag attached to
>a vacuum bag pulling 30" hg, in a Wabash single opening lamination press for
>30 minutes at 375 deg. F & 4500# total force. Upon visual inspection, the
>heatsink/pregreg package exhibited bubbles in every drilled hole. It this the
>result of resin starvation in the holes?
>
>
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>
>
We are successfully producing p.c.b. with buried heatsink (0.3 m"m x 2),
First we are laminating the heatsink with special prepreg from ARLON, to
allow as fill all the clearances in the heatsink and later final lamination.
(Contact with Mr. Harvy Beaman at ARLON).
Sh. Shalev
Eltek Ltd - Israel
Tel 972 3 9395050
Fax 972 3 9309581
E-mail : [log in to unmask]
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