Patent ID: 8444043

Claim:
A method of bonding substrates comprising: bonding an array of solder balls to one of a first substrate and a second substrate; forming an assembly of said first substrate, said second substrate, said array of solder balls, and a thermal-mass-increasing fixture, wherein said thermal-mass-increasing fixture is in contact with at least a peripheral surface of said second substrate; wherein said second substrate has a top surface and a bottom surface, wherein said top surface is more proximal to said first substrate than said bottom surface, and said thermal-mass-increasing fixture is in contact with a peripheral portion of said top surface; placing said assembly in a furnace, wherein said first substrate and said array of solder balls are heated to a higher temperature than said second substrate and said thermal-mass-increasing fixture; cooling said assembly while said thermal-mass-increasing fixture is in contact with said peripheral surface of said second substrate, wherein presence of said thermal-mass-increasing fixture in said assembly reduces a cool-down rate of a subset of said solder balls that is located at a periphery of said array; and separating a bonded structure including said first substrate, said second substrate, and said array of solder balls from said thermal-mass-increasing fixture after cooling of said assembly.