Our Process Engineering group was recently asked to evaluate a pad 
geometry for a standard SOT-23 transistor package.  The issue which 
brought us into this was poor placement and soldering capabilities.

Our DFM guide states the distance from the top edge of the two bottom 
pads to the bottom edge of the top pad to be 0.060" (0.040"w x 0.060"l pads.  
Center to center dimension of 0.100').  The Motorola recommended pad  spec.
 for the component states the same area between the pads should be 0.044"
 (.035"l x 0.031"w pad - center to center from top pad to bottom two 
pads is 0.079"). 

The SOT is placed  bottom side and  processed with centered double glue
 dots, convection cured and wave soldered. Our DFM states the recommended pads
from Motorola are for screen printing solder paste and reflow applications. 
I believe our DFM has the pads are too far apart regardless of the 
process. 

The question is for bottom side, glue, wave solder applications what 
pad geometries have been successful for SOT-23's? 

Side note: They have also stated that by elongating the pad from 
0.060' to 0.080" for wave solder applications they get better wetting to the
leads? Ever heard of this being done?

Regards,
Jim
Process Quality Engineer

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