According to industry sources, ATI decided to delay the production of 80nm chips at TSMC because the yields aren't good enough.
TSMC declined to comment on the report, citing customer confidentially, while ATI stated that its migration schedule to 80nm for 2006 has not changed, and it still plans to begin manufacturing on 65nm process technology in 2007.
The sources indicated that ATI originally planned to produce its graphics chips (RV560, RV570, RV505 and RV535) scheduled for release in the third quarter of this year using 80nm process technology. However, due to TSMC not being able to improve its yield rates, ATI will use 90nm node to manufacture the mid-range RV560 and RV570 chips.
More details over at DigiTimes. Originally, the Radeon X1900 was slated to be a 80nm chip but this changed to 90nm because of bad yields.