It's probably an old drawing...in those days most sn/pb was first
electroplated and then reflowed (fused, which is actually, technically
incorrect as the sn/pb had already been 'fused' in solution) using hot oil
or some form of heated fluorohydrocarbon (not so much anymore with the green
laws).

The fused sn/pb will provide a flatter surface than HASL.

Franklin



-----Original Message-----
From: Stadem, Richard [mailto:[log in to unmask]]
Sent: Tuesday, September 20, 2005 7:52 AM
To: [log in to unmask]
Subject: [TN] Fused tin lead plating versus HASL

Hi, folks
I have a pwb fab drawing that calls out fused tin-lead plating or solder
coating. I know that the solder coating is HASL, but what is fused
tin/lead? My understanding is that it is a tin/lead coating that is
applied to the bare pwb using a reflow oven process. Does this provide a
flat surface of tin/lead? If my only choice of finish is tin/lead, which
process is better in terms of flatness and solderability? I have a
fine-pitch BGA that is going to be assembled on this pwb.

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