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January 1999

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Subject:
From:
"Leslie O. Connally" <[log in to unmask]>
Reply To:
Leslie O. Connally
Date:
Wed, 6 Jan 1999 09:05:43 -0600
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text/plain
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text/plain (71 lines)
Hi Ed,

        We have been in the blind via plating technology for almost 2 decades
now and have had some success.  With Blind vias you come up against what is
known as a 'Faraday Cage Effect'. This effect prevents the equal exchange of
ions in the bottom of the hole, and is more pronounced at higher current
densities. When electroplating, even with Periodic Reverse plating, you can
expect only about 50% throw in the bottom of the hole. In the early '80s we
were plating 5 & 6 mil blind vias with about 80% throw in the bottom of the
hole
(1 mil on the surface and 0.8 mil in the bottom), but we were doing it with
electroless copper. We had to periodically bump the panel to insure release of
Hydrogen which could get entrained in the via and prevent plating. Now there
are vibrators that can do that for you. With electroless, the plating is much
slower, so the Ions in the hole have the time to be replaced, and mass transfer
is improved. The 'effective current density' (my reference) is very low and
therefore the surface of the panel dosen't tend to rob so many copper ions from
the hole.

I hope that this is of some help and doesn't sound like so much
'gobble-te-gook'.

Regards,
Les
>  From: "Eltek Ltd. - Process Engineering" <[log in to unmask]>, on
>  1/6/99 7:46 AM:
>  Hi technetters ,
>  I sent this meesage on 31 of December . Probably most of you were out of
>  e-mail due to new year . This is the second trial .
>  What are the  existing and working technologies for electrolytic copper and
>  tin lead plating of blind vias , laser drilled ?
>  We are testing now making tests with   0.2 mm diameter , 0.3 mm deep laser
>  drilled vias . The stage of permanganate desmear and electroless copper
>  plating was performed in vertical line without special efforts . We tried
>  different current densities in vertical electrolylic stage , but we got very
>  poor copper distribution along the wall : 20 microns in the upper part , 5
>  microns on the bottom and on the lower part of the wall . We just presume ,
>  tha the same problem will be for tin-lead stage of pattern plating .
>  Best regards and Happy New Year 1999 !
>  Edward Szpruch
>  Eltek Ltd - Israel
>  e-mail :  [log in to unmask]
>
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