We have seen this also.  On Cu/Ni/Au surfaces, the Ni mimicks the Cu and
the Au mimicks the Ni, so the resulting surface topography is a function
of the original Cu topography.  If the supplier can provide a uniform Cu
surface, then you stand a much better chance of yielding finished Au
metalization with uniform bondability.

Phil Yates
Nextek, Inc.

*****************************************
joef wrote:
> 
>      Besides hardness, our customer has indicated that underlying copper
>      surface topography (i.e., roughness) is a key factor - that, for
>      example, different surface prep methods prior to Ni/Au electroplate
>      (e.g., peroxide-sulfuric u-etch, persulfate u-etch, pumice w/ brushes,
>      pumice w/out brushes, even panel orientation relative to the
>      brushes!!) will affect wire bond yields.  Can anyone corroborate
>      this??  And if this theory holds, wouldn't a final pumice of the
>      plated gold surface itself improve things further?  Is there a
>      softness threshold below which an abrasive slurry could contaminate
>      the gold??
> 
>      J.Felts
>      PC World, Toronto
> 
> ______________________________ Reply Separator _________________________________
> Subject: Re: Wire Bonding
> Author:  [log in to unmask] at INET
> Date:    10/16/96 3:06 PM
> 
>      We also monitor Knoop hardness of the plated deposit from our soft
>      gold bath on a monthly basis. Knoop hardness should be under 80 knoop
>      for gold wire bonding.
> 
>      Kim
>      Hadco Ca.
> 
> 
> ______________________________ Reply Separator _________________________________
> Subject: Wire Bonding
> Author:  [log in to unmask] at SMTPLINK-HADCO
> Date:    10/15/96 7:08 PM
> 
> 
> Advice please !
> Is there a quantitative test that can be carried out on soft gold electroplate
> to qualify its suitability for wire bonding ?
>  Gold thickness and purity already to customers spec.
> Note in this instance gold is on a nickel undercoat.
> 
> Jim Douglas
> Kam Circuits
> 
> ***************************************************************************
> * TechNet mail list is provided as a service by IPC using SmartList v3.05 *
> ***************************************************************************
> * To unsubscribe from this list at any time, send a message to:           *
> * [log in to unmask] with <subject: unsubscribe> and no text.        *
> ***************************************************************************
> 
> 
> ***************************************************************************
> * TechNet mail list is provided as a service by IPC using SmartList v3.05 *
> ***************************************************************************
> * To unsubscribe from this list at any time, send a message to:           *
> * [log in to unmask] with <subject: unsubscribe> and no text.        *
> ***************************************************************************
> 
> 
> ***************************************************************************
> * TechNet mail list is provided as a service by IPC using SmartList v3.05 *
> ***************************************************************************
> * To unsubscribe from this list at any time, send a message to:           *
> * [log in to unmask] with <subject: unsubscribe> and no text.        *
> ***************************************************************************