Joint ache because of a board?

Heu!

Is it possible that my knees hurt because of board? I ride cable park and do big air tricks and high kicker hits. And I use flat board such as SS shredtown.

I doubt it.

My knees hurt a lot less after moving to a softer landing board (Ronix camber).. but my knees are shot anyway.

I went from a liquid force omega to a ronix one and kept the same bindings. The landings that used to hurt my knees and heels on the omega don't hurt on the one and the one also boosts me higher. I ride boat but it could work the same for cable. Maybe hire some different boards at your cable park if they do it and try it out

Yes, but your technique probably has more to do with it. I've ridden several boards that land terribly off big kicker tricks. Make sure wherever possible you land on edge.

If you go massive on kicker hits it will take its toll on your knees, doesnt matter what board you ride. Flex boards you can put the tail down first to soften the landing but at a certain point it just doesnt matter.

Never had knee problems until I got caught up in going massive on the kicker. Its hella fun, but it will take its toll.

I think we all have some pain in our knees lol. Over time it takes a toll. I too ride slingshots boards and they seem to ride better in a chop and smooth things out.
I also just got a new CWB with a spine that runs from tip to tail. I have only ridden it a couple times but it seems to really have solid landings and my knees haven't bothered me. That may not help you on the cable but it works for me behind the boat.

You may also wan to look at your stance and bindings they may be the culprit as well. If you are ducked out to far it can put tremendous stress on your knees and hips.

I have also be told by physical therapist and trainers to do leg workouts. You build up the muscles around the knees and hips to support them. This works believe me, after starting a leg program I have not had any problems at all.