But Harry,
        the query was only, why there was 1.1mils associated with the NI/Au?
Normal standards would call for 150 - 200 uinches of NI and upto 50uinches
of Au. Not 1.1mils!

Sincerely,
Brad Velander.

Lead PCB Designer
Norsat International Inc.
Microwave Products
Tel   (604) 292-9089 (direct line)
Fax  (604) 292-9010
email: [EMAIL PROTECTED]
http://www.norsat.com

See us at Booth S8155 at NAB 2002 in Las Vegas April 8 - 11.


> -----Original Message-----
> From: H. Selfridge [mailto:[EMAIL PROTECTED]]
> Sent: Thursday, April 04, 2002 10:34 AM
> To: Protel EDA Forum
> Subject: Re: [PEDA] WANTED: PCB Expert (Off Topic)
> 
> 
> Copper on a printed circuit is subject to severe oxidation 
> unless coated. 
> Cu oxides are poor electrical conductors.
> 
> Gold is a passive metal with excellent conductivity.
> 
> If you plate gold directly on copper, Au/Cu intermetallics 
> are formed that 
> cause the bond to be brittle and subject to mechanical 
> failure under stress.
> 
> Plating nickel over the copper forms a barrier that has desirable 
> intermetallic characteristics.  However, Ni also oxidizes 
> readily.  Ni 
> oxides are poor electrical conductors.
> 
> Plating Au over the Ni gives the best overall metallic 
> structure for a pcb 
> (pwb).  The Au is corrosion resistant, and has excellent 
> conductivity.  The 
> Ni barrier under the Au prevents Cu migration into the Au.  
> Ni/Au and Ni/Cu 
> intermetallics at the bonds are both hard and relatively durable.
> 
> That is half a semester in 5 lines that tells why nickel 
> plating is used 
> under gold on a pcb (pwb).

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