Method and apparatus for immersion cooling or an electronic board

Liquid heat sink apparatus for cooling electronic components mounted on a printed circuit board, comprising:

• (a) a cold plate mounted opposite said electronic components and substantially parallel to said printed circuit board;
• (b) means for containing a liquid coolant between said printed circuit board and said cold plate;
• (c) said liquid coolant contained between said printed circuit board and said cold plate and in thermal contact with said printed circuit board said electronic components mounted thereon, and said cold plate,
• wherein said cold plate is maintained a distance d from said electronic components sufficient to provide a Rayleigh number of at least 1700 in the equation ##EQU4## where g is the acceleration of gravity, .beta. is the volumetric coefficient of expansion of said liquid coolant, T.sub.1 is the temperature of said cold plate, T.sub.2 is the temperature of the component to be cooled, .nu. is the kinematic viscosity of said liquid coolant, and .alpha. is the thermal diffusivity of said liquid coolant;
• (d) means for maintaining said cold plate said distance d from said printed circuit board, comprising a sealed housing supporting said cold plate and surrounding said printed circuit board and attached thereto to thereby provide a sealed space for maintaining said liquid coolant herein;
• and
• (e) said sealed housing including means for accommodating expansion of said liquid coolant during thermal cycling.