How to create traces that don't touch for a four by four non matrix keyboard grid
Traces that need to cross on a circuit board are most often handled by using plated through via holes that can jump traces from one side to the other. 

If you build your key pad out of tact switches like these they are designed to often have pairs of their terminals shorted across in the switch body. This can perform an automatic trace jump capability for a trace that can pass under the switch body on the circuit board.