Depends on the climb rate i.e. power versus weight, and operating ceiling.
If it can climb at 3000fpm, and has TKS props, and can climb at that rate all the way to say 20k feet, it won't get a chance to pick up much ice. You just need to avoid doing this in CBs etc
For most practical planes that would tend to imply turboprop engines though and most of those are pressurised for marketing reasons.