The SMT Plus book has at least 10 different SOT-23 footprints.

Measured from outer edges of the pads:

For reflow:
  Smallest:  2.54mm x 1.65mm
  Largest:    3.45mm x 3.05mm

For wave solder:
  3.48mm x 2.82mm


John Williams


----- Original Message -----
From: "Ian Wilson" <[EMAIL PROTECTED]>
To: "Protel EDA Forum" <[EMAIL PROTECTED]>
Sent: Monday, August 12, 2002 5:14 PM
Subject: Re: [PEDA] Philips Wave and Reflow Footprints(Ex:IPC Footprint
Standards)


> As an example:
>
> The SOT23 reflow footprint takes up 3.3x3 mm while the wave takes up
4.5x4.6mm.
>
> The IPC standard has a 8x8!! placement courtyard. Like, yeah right.
Someone
> tell me this is a typo - at that size I may as well us a TO-92.
>
> Taking the distance of the outer edge of a pad on one side of the SOT-23
to
> the outer edge of the other pad (the IPC Z dimension):
>
> Philips Reflow: 2.7mm
> My footprint: 2.95 mm
> IPC: 3.6mm
> Philips Wave: 4mm
>
> In high density layouts what are you going to use?  (Actually, I am a bit
> timid going as low as the Philips reflow footprint as it feels mighty
small
> when you see it -it is not easy to hand solder.  But the point about
reflow
> footprints being able to be made very small is clear.  My footprint has
> been in use for many years, on many boards, assembled by many
manufacturers
> without any issues.)
>
> Also, if you have a look at the Philips wave footprint
>
http://www.semiconductors.philips.com/acrobat/packages/footprint/FOOTPRINT-S
OT23.pdf
>
> You can see that the single pad is very wide.  This is different from the
> old data I have from the early to mid 90's so they have updated it.  Also,
> I think they have changed the preferred wave direction - I think it used
to
> be in the other direction.  I am not sure I like the new wave footprint
but
> maybe it heats the device more evenly or something.
>
> Ian
>




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