I have a DB25 I/O connector, thru-hole. The pins connect to an SMT MCU, which I want to protect from ESD, specifically IEC 61000-4-2. I want to use SMT Zener diodes to protect the pins.
I am considering various layouts. I imagine the optimal layout would have the diodes between the DB25 and the MCU. In this way, an ESD event can be shunted to ground before it gets to the MCU
MCU <-> Diodes <-> DB25
However, I would like to take advantage of the thru-holes in the DB25 to simplify routing and reduce the number of vias that I would need. However, in doing so, the diodes will end up on the "other side" of the DB25.
MCU <-> DB25 <-> Diodes
Is this a bad idea? I'm slightly concerned about whether a sufficiently fast ESD strike could "split up" and reach the MCU before the diodes begin fully conducting.
If this is the case, would it be mitigated if the MCU <-> DB25 traces were run on bottom-layer, while DB25 <-> Diodes traces were on the top layer? Would the added vias between the MCU and DB25 encourage the ESD current to go through the diode instead?