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February 1999

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Subject:
Re: Sn composition/thickness on vertical and horizontal pads
From:
Gabriela Bogdan <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Sat, 13 Feb 1999 12:47:48 +0200
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text/plain
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text/plain (54 lines) 
etgar wrote:

> Fellow Technetters:
>
> I had been measuring solder thickness on QFPs and found out that the
> thickness on horizontal pads is slightly thicker than the vertical
> pads. I
> know this is normal specially for a Vertical Hot Air solder leveler.
> But
> what should be the limit? Also along with test, using an x-ray coating
>
> thickness measuring machine, is it normal that the tin % composition
> on the
> vertical pads lower than horizontal pads? I tried lowering the air
> knife
> pressure thinking that high temperature depletes Sn, but I got similar
> data
> on 200, 210, 220, 230 and 240 C air knife spray pressure.
>
> Garret Dimaculangan
>
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  Hi!
I experienced the same with solder thicknesses under 3 um.
More experienced Netters could explain us maybe if it is related to
intermetallic formation .
Gaby

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