Jim, I use a regular 1/4" bit to do mine on the router table. I quit doing it on the router table because I was getting blow out from the router bit. You will do better with a box joint TS blade. As far as I know, there is no such thing as a box joint router bit.
https://www.amazon.com/Freud-20T-Jo...78&sr=8-1&keywords=freud+box+joint+cutter+set
https://www.amazon.com/Freud-20T-Jo...78&sr=8-1&keywords=freud+box+joint+cutter+set