Pablo Mesa asked:

>    Can anyone tell me the IPC prefered pad size for bottom side SOT23
>packages?

My advice to you is use an infinitely small pad.

No matter what pad size we use, we get opens trying to wave solder those
damn SOT 23 diodes. This is one of my biggest chronic solder defects on
some older designs which refuse to die.

Start yelling now to have them put on the top and reflowed with paste,
everyone I know has problems with wavesoldering LED's.

If the IPC pad or any variation thereof will help, please tell me, too. I'm
sure the pads (0.050" x 0.037") we use are larger than the IPC
recommendation, which generally increases the volume of solder for the
joint, but we still get too many opens. Our pads look like this:

 __      __
|  |    |  |
|__| __ |__|
      |
   0.045"       ----> solder direction
     _|_
    |  |
    |__|

Motorola recommends a rectangular pad 0.035" x 0.031", which I believe
would  work well for paste print/reflow.


good luck,


Jerry Cupples
Interphase Corporation
Dallas, TX
http://www.iphase.com/