Forming solder balls on substrates
AssigneeWstp, LLC
InventorsJohn MacKay, Tom Molinaro
Life of this patent
Estimating the term…
Abstract
A mask (stencil) having cells (openings) is disposed on a surface of a heater stage, and is then filled (printed) with solder paste. Then a substrate is assembled to the opposite side of the mask. Then the solder paste is reflowed. This may be done partially inverted. Then the mask is separated from the substrate, either before or after cooling. Solder balls are thus formed on the substrate, which may be a semiconductor wafer. A biased chuck urges the substrate into intimate contact with the mask. A method for printing the mask with solder paste is described. Methods of forming high aspect ratio solder bumps (including balls and reflowable interconnect structures) are described.
Claims11
Method for forming solder bumps on a substrate having a plurality of pads on a surface thereof, comprising:
- providing a mask having a first surface and a second surface, and a plurality of cells extending from the first surface at least partially through the mask to the second surface thereof;
- filling the cells with solder paste;
- disposing a substrate in a chuck assembly;
- disposing the mask on a surface of the substrate with the first surface of the mask adjacent to the surface of the substrate;
- urging the substrate into positive contact with the mask by allowing the substrate to flex under pressure so as to maintain substantially intimate contact between the first surface of the mask and the surface of the substrate;
- applying a pressure plate to the second surface of the mask with sufficient force to capture the cells between the plate and substrate and to limit mask warping during solder reflow;
- reflowing the solder paste;
- and
- separating the substrate from the mask.
Dependencies are inferred from the claim text.