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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
>
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