Comments on Is it allowed to skip a pin to increase creepage distance?
Parent
Is it allowed to skip a pin to increase creepage distance?
From IEC-62368 for signals below 30kHz the creepage distance for pollution degree 2 and material group IIIa,IIIb (FR-4 boards are IIIa) at 40V is specified to be 1.1mm. We have a connector that has many BGA pads, and the copper-to-copper distance is 0.635mm:
Putting a slit between is not an option, the only way I could see is to add coating after assembly that would allow to use values for pollution degree 1, which would be 0.16mm, quite a drastic reduction.
One of the engineers mentioned that leaving a pin floating in between also counts towards increasing creepage, but I am not sure about that. The definition of creepage that is used in standard:
Creepage is the shortest path between two conductive parts measured along the surface of a solid insulating material
It would imply that it does not matter if the pin in between is floating or not, but on the other hand, how would the voltage be defined if one of the pins is floating? The voltage could be anything between those two pins! In my mind the pin would have to be physically removed from the connector body for this to be valid, and the pad removed from PCB.
Can anyone comment on the validity of such interpretations of creepage? If you have experience with other standards please share it, IEC is just where I got the numbers from.
Post
[ If this is a certification and compliance matter, then you should run your question and your findings by your test lab, certifying body, specialist safety reviwer. ]
Gaps on either side of a floating pin count towards creepage. I've seen it done when Molex KK 396 connector carries mains AC voltage. The distance between adjacent didn't satisfy creepage requirement. We changed the connector from 2-pin to 3-pin with the middle pin floating.
[...] the only way I could see is to add coating after assembly that would allow to use values for pollution degree 1, which would be 0.16mm, quite a drastic reduction.
Underfill under BGAs is an established process. Even if you have voids, the sealed space under the connector could give you pollution degree 1.
I've also seen underfill for high voltage insulation too. It was an analog mux for ultrasound. ±100V excitation pulses went through it.
1 comment thread
1 comment thread