Since the year 2000, Würth Elektronik has series produced thin TWINflex 
4-layer microvia circuit boards on aluminium heat sinks in various shapes and sizes for automotive applications, e.g. transmission control.
The highlights of this heat sink technology:
- specified for ambient temperatures of -40°C to +125°C
- thin circuit board for good heat conduction and high cycle stability
- heat sink applications offer optimised thermal management
- different heat sink thicknesses possible
- aramide epoxy in the core for CTE control or FR4 material
- the buildup layers are RCC with high Tg epoxy or FR4 prepreg material
- photosensitive solder-stop, surface chem. Ni/Au
- suitable for Al wire bonding- conductor tracks and separations 6 mil or 5 mil- staggered thermal microvias
- high component density, and also high wiring density possible- low thermal resistance
- blind and buried microvias possible possible across 4 layers
- individual shapes possible