Patent ID: 6222277
Filing Date: 2001-04-24
Classification: H01L,H05K,Y02P

Abstract:
A method for forming an interconnection attaching a semiconductor device to a printed circuit board comprising:providing a semiconductor device;attaching a first plurality of balls formed of a first solder alloy on the bottom surface of the semiconductor device whereupon the balls project downwardly from the bottom surface, the first plurality of balls sized to be effective to support the weight of the semiconductor device;attaching a second plurality of balls formed of a second solder alloy on the bottom surface of the semiconductor device whereupon the balls project downwardly from the bottom surface, the second solder alloy having a liquidus temperature lower than the first solder alloy liquidus temperature;providing a printed circuit board having a top surface and a bottom surface, the printed circuit board also having a plurality of solder wettable pads disposed on the top surface of the printed circuit board, the semiconductor device and the printed circuit comprised of material taken from the same group of materials such that the coefficient of thermal expansion for the materials comprising the semiconductor device and the printed circuit board are approximately equal;placing the semiconductor device over the printed circuit board such that the each one of the first and second plurality of solder balls of the semiconductor device is positioned above a corresponding one of the plurality of wettable pads on the printed circuit board;heating the semiconductor device, the printed circuit board, the first and second pluralities of solder balls to a temperature that is above the liquidus temperature of the first solder alloy and below the liquidus temperature of the second solder alloy, such that each of one of the second plurality of solder balls flows on the corresponding wettable pad of the printed circuit board, and such that the during the heating the first plurality of solder balls remain solid to prevent collapse of the first plurality of solder balls; andcooling the ball grid array and the printed circuit board to solidify the second solder alloy to complete attachment of the semiconductor device and the printed circuit board.