When depaneling boards with break-away tabs, you must use a fixture to
evenly distribute the breaking forces. Not to do so will most certainly
cause adverse effects on the board. In addition, the tab design should
minimize the forces requried, but maintain the panel in a rigid form for
processing.

What does all this mean? There are many methods for designing strength into
a tab. A series of small drilled holes in the tab, will aid in breaking and
keep the panel rigid. 

regards,

Gary Ferrari
Tech Circuits