Both Altera and Xilinx were on TSMC. Altera wanted an Edge over Xilinx, at the time Intel was committing ( on paper ) to their Custom Foundry. Altera switched and bet to Intel Custom Foundry. Nothing ever worked out with Intel Custom Foundry because they were not used to working with others on Foundry Process. Intel thought the problem was with Altera not being part of company and they had too much cash so they might as well buy them for better synergy. And it did, getting internal access seems to have ( on paper or slides ) speed things up with product launches and roadmap, until they hit the Intel 10nm fiasco.