Patent ID: 7977155

Claim:
A method of forming an integrated circuit structure, the method comprising: providing an interposer wafer comprising: first bonding conductors on a first side of the interposer wafer; and second bonding conductors on a second side of the interposer wafer opposite the first side, wherein the second bonding conductors are electrically coupled to the first bonding conductors through routing connections in the interposer wafer; providing a die comprising solder bumps thereon; applying a compound underfill onto the first bonding conductors of the interposer wafer, wherein the compound underfill comprises an underfill material and a flux material, wherein the flux material is hydrophobic, and wherein at least portions of the first bonding conductors are buried in the compound underfill; aligning the die to the interposer wafer and pressing the die against the compound underfill, so that the solder bumps on the die penetrate the compound underfill and contact the first bonding conductors; reflowing the solder bumps; curing the compound underfill; applying the compound underfill onto the die after the step of reflowing; and bonding an additional die onto the die.