Does my son apply for Business Visa?

I have been living in China since last two years on employment work permit. My son has completed his 12 std and his X type one was converted to L type. Before he leaves for his under graduation abroad starting Feb 2014 he would like to do an internship while we are in Shanghai. Does he need to convert his L type to F type if he wants to work as an intern? Does he need to exit PRC to apply for a F type one? Can he extend his F type one for more than 3 months while he is in shanghai?