Electroplated Cu thickness distribution offers some  challenges for the 
manufacturer. 
 
Examples:
    *   Hi aspect ratio holes require a "high throw" bath so as not  to 
over plate the entry and the exit to the hole. Throwing power is the ratio  
between thickness in the middle of the hole as compared to the entry or  
surface of the hole. A 100 % throw means the entry and the middle of the  hole are 
of the same thickness. A bath at 50% throw will plate 2 mils on the  
surface to achieve 1 mil in the middle of the hole. The higher the aspect  ratio 
the greater the challenge. 
    *   Isolated Traces or pads: these are high current density  areas, as 
compared fro example to a larger ground plain area (low current  density). 
Current distribution is a function of the pattern being  plated.
If we combine the 2 examples meaning a high aspect ratio hole  (> 10 :1) 
with uneven surface pattern  (large ground plain area and  isolated 
traces/pads) and a 50% throwing bath, you could easily see 4 -5 mils of  plating in 
the isolated areas.
 
What is the answer?
 
The designer could help by minimizing incidents of extreme  isolation; or 
add dummy lines or pads around the isolation.
The  manufacturer must use a high throw bath for these challenging parts. 
He must optimize his plating cell configuration.
He has to plate these parts at lower current density for a  longer time 
(example (12 ASF for 100 minutes or less for longer).
 
Restricting an upper limit for plating is a reasonable  approach if the 
higher thickness is problematic. The question is where do you place the upper 
limit? )0.0025" may be too  restrictive for challenging parts as stated above 
and 0.005 is way too  high.
 

Best Regards  
George Milad
Nat'l Accts Mgr for Technology
Uyemura International  corp
516 901 3874








In a message dated 3/1/2012 6:55:13 A.M. Eastern Standard  Time, 
[log in to unmask] writes:

Hello  all - We call out a minimum of .001 inches of copper plating on the 
walls of  our holes in our standard fabrication notes.  We don't mention any 
min or  max on exposed lands and lines. We recently received a board that 
upon  cross-section analysis we discovered it had an additional .005 inches 
of  copper plated up on the top and bottom of the board.  We are considering  
listing a maximum in our drawing notes as follows:  "PLATING PROCESS  SHALL 
NOT PRODUCE MORE THAN AN ADDITIONAL .0025 INCHES OF COPPER ON EXPOSED  
LANDS AND LINES."  Anyone have any comments or suggestions for us?   Thanks in 
advance.  





______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask] 
______________________________________________________________________