Conventional electroplating from aqueous solutions, as opposed to molten
salt and organic solutions, inherently and instantly creates oxides,
hydroxides etc with non-nobel metals such as Si, Ti, Cr, Al, Ni etc. Thus,
the subsequent plating process takes place on such oxidized substrate. From
that point on the quality of plating depends on many factors including
uniformity of oxide, ahesion of oxide to substrate as well as to the plated
metal, conductivity of oxide etc. That is why it is always good to minimize
the risk of substrate oxidation and have a seed layer such as Au or Cu (Cu
oxide if formed in water is week and can be easily reduced with adequate
plating procedure).

----- Original Message -----
From: "Ravi Shankar" 
To: 
Sent: Thursday, January 08, 2009 1:33 AM
Subject: [mems-talk] Au electroplating on Al substrate


> Hi Denis Petrov,
>
>               I came across a similar situtation before and yes, Au
> was not electroplated on to the Aluminum substrate... in my
> experiment, a sulfite based Au plating solution was used, and even
> after 1 hour,   au was not plated on al substrate... i guess it may be
> becos of adhesion related issues, since Au was getting plated on Cr
> substrate (however, surafce quality of plated gold on Cr substrate was
> poor).... interested to know the exact reason, if anyone can explain..