I am not beting exact on the actual thickness of the Ni/Au as its not
specified in the board report, only that the outer serfaces are plated to
1oz, part of that plating will be copper when the via and through hole
connections are made.

The manufacturers report only states the plate thickness, not the proportion
of Ni/Au to Cu.

j.


-----Original Message-----
From: Brad Velander [mailto:[EMAIL PROTECTED]]
Sent: 04 April 2002 20:00
To: 'Protel EDA Forum'
Subject: Re: [PEDA] WANTED: PCB Expert (Off Topic)


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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