A company called PC Power & Cooling makes a stick-on cooling fan for the 486 and Pentium processors that just happens to fit the 68040 perfectly. The fan uses a stick-on backing to attach to the chip, so you don't have to mess with little clips or spring wires. It spins on ball bearings instead of a bushing, so life expectancy is claimed to be 50,000 hours instead of the ordinary bushing fan's 5000 hours. A disk-drive power connector powers the fan. Finally, it's only .6 inches high, no more than the heat sink that comes with the A3640 processor board. PC Power & Cooling calls it by several names; the best one to use is the "PENTA-COOL 54" for the 90 MHz Pentium or the "CPU-COOL 1.9."
Some earlier versions of the fan had "corners" cast into the aluminum heat sink to better fit the 486; these versions don't fit the 68040 without modification, so ask for either of the versions above, or make sure they know that the one you're purchasing must be of the flat variety.
In the United States, you can usually save a few dollars by ordering these fans from large mail-order companies like PC Connection, but please make sure of the model and brand first.
PC Power & Cooling
5995 Avenida Encinas
Carlsbad CA 92008
(619) 931-6988 Fax