Hi Pankaj,
You are not providing complete information, which leads me to believe that 
you do ot have complete understanding of the issues involved.
You say: "...we find the tin plated PCB has much more oval shaped joint then 
gold plated...[on] the oval shape pad[s]...[with the] same reflow profile."
You thus indicate you get different reflow wetting. What you do not indicated 
is what is underneath either the tin or the gold plating. I would suspect 
that you have copper under the Sn plating and nickel under the Au plating. 
It takes significantly more heat to get good dissolution of Ni in Sn than Cu; 
thus, you need a higher reflow temperature [~15°C] for reflow soldering to Ni.

Werner Engelmaier
Engelmaier Associates, L.C.
Electronic Packaging, Interconnection and Reliability Consulting
7 Jasmine Run
Ormond Beach, FL  32174  USA
Phone: 904-437-8747, Fax: 904-437-8737
E-mail: [log in to unmask], Website: www.engelmaier.com 

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