I'm in my last year of an MS in Mechanical Engineering and considering a PhD. I've noticed some companies (Google, Microsoft Research, Apple) offer PhD programs or sponsor PhD students. What are the trade offs between an industry sponsored PhD and a traditional academic one? My main concern is that an industry PhD might limit my research freedom and make it harder to go into academia later. On the other hand the pay difference is huge (industry PhDs often get full salary vs academic stipend). Anyone have experience with this?