Pad spacing is just one element to consider. Your pad spacing is determined by the pitch (center to center distance between the leads). There are several good resources to find the appropriate pitch per device. Search the archives here or refer to the manufacturers spec for each device.
Secondly, you must consider paste volume. Even with the most perfect pad design, you can still get bridging if you put too much paste on the pads. Again, search the archives for references or use IPC-7525 "Stencil Design Guidelines"
Third - you need a solder mask dam between pads (especially critical for fine pitch, under 16 mils).
Fourth - a reflow profile that gets hot too quick can cause paste to wick up the leads and create bridging.
Fifth - paste print alignment is critical, the paste deposit must be centered on the pads. Use 10X magnification to see if you have good alignment. Offset printing will encourage the paste to bridge, jump across the solder dam, even if all other process attributes are perfect.
You must consider all of the 5 basics described above before you can determine what is the root cause of your bridging.
Please describe your process in more detail if you still need more help.
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