The dimensions of the 8-pad uDFN package is a mere 2mm x 2mm x 0.5mm, and weighs a scant 8mg.
Atmel's uDFN is a surface mount plastic low-profile Chip Scale Package (CSP). It has moderate thermal dissipation. Pads are located on two sides of the package.
The largest ATtiny available in uDFN has 1KBytes Flash.
ΘJA = 96.602°C/W - "theta J A", this is the thermal resistance junction-to-ambient. Number obtained from simulation software and is meant as a guidelne only. Engineers should perform their own thermal tests to verify operation in their system.
According to Atmel. ATtiny microcontrollers in uDFN packages are available now. Pricing starts at $0.52 US @ 10Ku.
"Atmel Corporation (Nasdaq: ATML) is a worldwide leader in the design and manufacture of microcontrollers, capacitive touch solutions, advanced logic, mixed-signal, nonvolatile memory and radio frequency (RF) components. Leveraging one of the industry's broadest intellectual property (IP) technology portfolios, Atmel is able to provide the electronics industry with complete system solutions focused on consumer, industrial, security, communications, computing and automotive markets."