Hi,
I have used both same size pads and different size pads for reflow/wave
soldering and have come to the conclusion that slightly longer pads (0.5 mm)
show advantages on wave soldering compared to reflow.
This is because taller components tend to shield the footprint from the chip
wave which can lead to skipped or open joints. The longer pads help to
capture the solder and lead it into the joint.
If you are wave soldering in-line gull wing devices, then orientate them so
that each footprint/lead goes through the solder wave one after the other.
This will prevent shielding one side of the device. Extra pads at the output
end, known as 'solder thieves' will aid drainage of the molten solder and
help prevent shorts. Orientation of these devices on the reflow side is not
an issue.
My experience also says that reflow soldering inherently gives lower defect
levels so I try to design wave soldering out of the equation. Double sided
reflow and pin in hole reflow help here.
Regards
Eric Dawson

> -----Original Message-----
> From: Cathy Killen [SMTP:[log in to unmask]]
> Sent: 10 August 2001 13:48
> To:   [log in to unmask]
> Subject:      [TN] SMT Pads
>
> Hi,
> Is there a difference in SMT pad/land size at the design stage if the PCB
> is
> to be reflowed or wave soldered?
> Cathy Killen
> Training Instructor
> [log in to unmask] <mailto:[log in to unmask]>
> An Oasis of Training Excellence
> *       028 38314305
>
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