Hi Edward:
     
     Sorry for the late response.
     
     Your inquiry is quite interesting.  Lowering your ASF to 10 may put a 
     strain on your brightner system as some go out of control at that 
     current density over a long period of time.  Lowering your ASF is sure 
     to improve the throwing power, especially on those 10:1 aspect ratio 
     panels.  However, to improve surface distribution you must get the 
     anode/cathode distance further apart.  If space is a factor as you 
     mentioned, you may consider using smaller diameter anodes and more of 
     them.  Make sure to keep your voltage high enough as again, you may 
     imbalance your brightner and loosen your anode film.  Good luck!


______________________________ Reply Separator _________________________________
Subject: Pattern plating considerations
Author:  [log in to unmask] at corp
Date:    3/19/97 4:57 AM


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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