Patent ID: 9721919
Date: 2017-08-01
CPC Classifications: B23K,H01L

Claim:
1. A method to form solder bumps on a substrate, comprising: placing a first solder ball mask on a solder ball fixture, wherein the solder ball fixture comprises a first array of cavities and a second array of cavities formed in a surface of the solder ball fixture, wherein the first solder ball mask comprises a first array of openings aligned to the first array of cavities of the solder ball fixture; utilizing the first solder ball mask to place a first set of preformed solder balls into the first array of cavities through the first array of openings, wherein the first solder ball mask prevents the first set of preformed solder balls from being placed into the second array of cavities of the solder ball fixture; removing the first solder ball mask from the solder ball fixture, and placing a second solder ball mask on the solder ball fixture, wherein the second solder ball mask comprises a second array of openings aligned to the second array of cavities of the solder ball fixture; utilizing the second solder ball mask to place a second set of preformed solder balls into the second array of cavities through the second array of openings; removing the second solder ball mask from the solder ball fixture; placing a substrate on the solder ball fixture, wherein the substrate comprises a first array of contact pads aligned to, and in contact with, the first set of preformed solder balls disposed in the first array of cavities of the solder ball fixture, and wherein the substrate comprises a second array of contact pads aligned to, and in contact with, the second set of preformed solder balls disposed in the second array of cavities of the solder ball fixture: performing a solder reflow process while the substrate is placed on the solder ball fixture to heat the preformed solder balls and bond the first set of preformed solder balls to the first array of contact pads of the substrate and bond the second set of preformed solder balls to the second array of contact pads of the substrate; and removing the solder ball fixture from the semiconductor substrate after the solder reflow process is completed; wherein the first and second sets of preformed solder balls differ in size, wherein the preformed solder balls of the first set of preformed solder balls have a diameter D wherein the first array of cavities and the second array of cavities formed in the surface of the solder ball fixture are sized and shaped such that top portions of each of the first and second sets of preformed solder balls, which protrude from the first and second arrays of cavities past the surface of the solder ball fixture, are coplanar.