Abstract:
A method is disclosed for producing a brush-like heat exchanging structure on a semiconductor device chip. A given amount of ferromagnetic powder is distributed uniformly in an electroless plating bath. Completed semiconductor device wafers are placed at the bottom of the bath, the rear wafer surfaces facing upward. An array of poles of a single electro-magnet is placed immediately below each wafer, each pole registering with a respective chip position on the wafer. The ferro-magnetic powder is permitted to settle on the rear surfaces of the wafers and then current is applied to each electro-magnet attracting substantially equal amounts of ferro-magnetic powder toward each magnet pole. This results in the erection of brush-like structures of ferromagnetic particles on the rear surfaces of the wafer opposite the individual poles. The bath temperature is then raised to the required operating temperature for electroless plating while each electro magnet remains energized. A uniform deposit of electroless metal transforms the brush-like structures into rigid heat exchangers firmly attached to each wafer at the chip locations. The wafers are then diced to yield individual chips each having its own heat exchanging structure.