Is it possible that maybe on planet Mars the iron was the computer chassis while titanium and aluminum alloy was the main material used in circuits?
Sure. It's also possible that it's a planet sized golf ball build by a race of cosmic, golf obsessed hamsters. That said, until there's any reason to assume so (such as a label), there's no reason to assume so.
Is there enough evidence right now to run out the possibility that computers or electrical circuits or semiconductors existed on Mars?
Well, since we only mapped a very small portion of the surface, and not with the best instruments, there's no evidence available for the absence of decomposed ancient computers of unknown composition, make and style. There's no evidence of absence of donuts a million years ago on Mars either.
Why is steel or iron never mentioned at all in the construction of PCB's or hook up wire?
Bad parameters for those tasks. Bad conductivity, solderability and a host of other problems. Basically, you try to go with what's best based on a lot of parameters. You COULD probably build electronics using iron instead of copper, with great sacrifices, but there's no reason at all to do so.
Is it possible that something can be done to prevent rust in the manufacturing of PCB with iron traces? Everything is plated or covered in conformal coating anyway.
Sure, you can plate it with things, coat it in whatever you wish, make corrosion resistant alloys.