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bridging between 2 pads

steven

#18097

bridging between 2 pads | 7 November, 2001

what is ideal or minimun spacing in between 2 pads to avoid bridging? thanks

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Michael Parker

#18100

bridging between 2 pads | 7 November, 2001

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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#18106

bridging between 2 pads | 7 November, 2001

If you don�t paste / reflow solder on the pads, they will never bridge. ;-)

A design with a 0.13mm gap between pads will challenge equipment, materials, and process.

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steven

#18109

bridging between 2 pads | 7 November, 2001

sometime hand solder can cause also. no necessary have to be paste n reflow.:) now i'm facing bridging on 0402 components pads. any suggestions on spacing distance as we're going to re-design the pcb.

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#18112

bridging between 2 pads | 7 November, 2001

Consider using the following hierarchy of rules for pad design: 1. If you have a land pattern in a manufacturer�s data sheet, use it. 2. If the data sheet doesn't have a land pattern, but does have an RLP (registered land pattern) number or JEDEC number, try SM-782 and use the land pattern there, if there is one. 3. If 1 and 2 fail, use the IPC calculator [free at http://www.ipc.org] and take the heel and toe solder joint figures required from table 3.4 in SM-782. 4. If in practice later, the resultant pattern doesn't work, well, you're largely on your own [with your pals at SMTnet] to sort out a better solution.

Hint. The RLP Number for a 0402 is 1005.

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