# Component case size and spacing for ESD protection circuit

As im searching for TVS diodes, I see a 30KV rated diode array has pins RIGHT next to each other. Aren't they so close that a spark can easily jump between pins??

I read a few time that you need a certain case size for protection components so that Sparks don't jump the components, yet I see 30KV rated bidirectional TVS diodes with a 0402 case size!

I need to make my protection circuit as compact as possible and as high rated as possible. I'm having a hard time finding component size, and spacing guide. Anyone can help? Thanks!

• Somewhat facetious: The TVS diodes are there to prevent the energy from going further 'downstream'. They do that by going conductive at high voltages. Any sparking along the outside is great as all that energy no longer has to go through the diodes. Oct 9, 2019 at 12:24
• I guess that does make some sense. But do you know of any guides or recommendations for other component spacing? I was going to do series resistor --> cap --> TVS --> series resistor --> cap --> input. Should I remove the ground copper pour under each component? These protected inputs are just monitoring switch closures. Recognition time isn't important Oct 9, 2019 at 12:34
• Smaller packages for TVS are actually an advantage, since they have lower inductance. Helpful hint: don't thwart this advantage (with any size TVS) by attaching it with long signal/ground lines. Best practice is to have one pad on the signal line (so that no signal can get onto the board without passing that pad) and the other on the shortest possible path to the ground plane...and the TVS as close to the entry point as possible, so the ESD can't arc to another node before getting to the TVS. If you're going to put a guard at the door, you make sure all visitors have to go past the guard. Oct 9, 2019 at 15:04
• Right, I understand this, but id need to lower and slow the power entering the TVS, I will have a series high pulse resistor with parallel high voltage capacitor before TVS. My main concern is arch jumping across resistor rather than through it. Is there a case code and distance I should maintain between input terminal, resistor and capacitor? Oct 9, 2019 at 15:10

As you can see, at a 30kV test voltage, the current through the device will be approximately 30kV/300$$\\Omega\$$= 91A, which typically corresponds to Ipp (peak pulse current) in the datasheet. For example a 3.0SMCJ20AQ with a standoff voltage of 20V will clamp an Ipp of 92.6A to less than 32.4V. So, for example, a voltage regulator with an absolute maximum input voltage of 35V should be protected in the test situation.