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Date: | Wed, 19 Mar 1997 08:10:55 +0200 (IST) |
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Hi Technetters !
We are in preliminary stage of design the expansion of the existing pattern
plating line ( acid copper + tin-lead ) . Most of our PCB are SMT and back
planes , up to 2.4 mm thick , 0.30 mm drilled vias , 4 - 5 mill conductors
on the outer layers . The external pattern is not equal , lot of isolated
pads and conductors . The next goal is 3.6 mm thich and 0.25 mm drilled vias
. The existing cathode - anode distance is only 4 inch . Most of the boards
are plated with current dencities in range approx. 20 ASF 60 minutes . More
complicated and with high aspect ratio : double time and half of current
dencity . Normally , we are traing to compensate uneven pattern by adding
non - functional pads on the outer layers .
Since the available space for further expansion is limited , we have to
decide which one of basic approaches should be considered :
1 ) Keep the existing cathode - anode distance , but to plate with low
current dencity ( 10 ASF ) 120 minutes .
2 ) Go to larger anode-cathode distance ( say 10 inches ) , keep the
existing plating time ( 60 minutes ) and the current dencity ( 20 ASF )
Basic points for decision :
1 ) Better surface - hole plated copper distribution in high aspect ratios
2 ) Better surface distribution to avoid overplating on isolated pads and
conductors to avoid severe overplating problems .
Your comments will be very appreciated !
Edward Szpruch
Eltek Ltd - Israel
Tel 972 3 9395050
Fax 972 3 9309581
E-mail : [log in to unmask]
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