DigiTimes reports both NVIDIA and Qualcomm are approaching other foundries as a second source for 28nm production due to the tight supply of 28nm capacity at TSMC:
The reported tight supply of chips built using TSMC's 28nm process technology is likely to drive Nvidia and Qualcomm toward other foundries as a second source, industry sources have revealed. Nvidia has begun sampling its chips on Samsung Electronics' 28nm process technology, the sources indicated. The GPU vendor contracts only TSMC to manufacture its products at present.
Also acknowledging the tightness of TSMC's 28nm manufacturing capacity, Qualcomm has approached United Microelectronics (UMC) and Globalfoundries for additional capacity, the sources observed.
TSMC reportedly is having yield problems with its 28nm nodes causing the difficulty in ramping up the process capacity. There is also speculation that the foundry had been trying to control the availability of its 28nm capacity as insufficient yield rates would affect its gross margin performance.