Problems to solve
HP engineers still face a number of tricky engineering hurdles. Inkjet printers deposit ink on paper. What HP is proposing is to reuse the fluid, which will likely mean building a tiny reservoir into the processor die itself and then engineering a circulation system of some sort. A far more serious problem is one of fluid thermodynamics, far away from HPs traditional expertise in electrical engineering. Inkjet printers use the finest mist possible to increase resolution. But if the fluid is too fine, the particles wont have enough momentum to actually overcome the rising heated air from the chip, said Ratnesh Sharma, also a member of HPs technical staff. Worse still, heavier droplets will actually pool on the chips surface. While the drops will initially cool the chip, the pool actually serves as an insulator, again allowing the heat levels to rise. Researchers said that HP will likely use some sort of inductive fluid, not water, which wont short out any electrical connections."Its like taking a shower in the morning and saying let me get more water on my nose and ears instead of a constant stream of water," Patel said. Finding a chip to apply the technology to is another problem. While HP co-designed the Itanium processor and its own PA-RISC architecture, the company is phasing out its proprietary lines and buying Intels chips instead. HP might not be able to convince Intel to ship it bare processor dice, allowing it to add its own cooling package, executives admitted. Instead, the technology might be more practical in laser diodes, used in optical communications, they said. Sensing the patterns of heat is difficult as well. HPs software engineers can only predict so much. Processors today are typically monitored by a single thermal diode embedded in the chip. HPs system could require several, although they would also need their own I/O pins in the chips package. "What we need is real data," Bash said. However, design engineers havent traditionally made thermal issues a priority. In an HP chip, "we had to fight to just get one (diode)," he said. "They screamed."
In addition, if the thermal density pattern on a chip varies, then the cooling must change as well. HPs Sharma demonstrated a system by which different micronozzles in the cartridge pulsed a fine mist over different areas of the chip. The individual droplets are picoliters in size.