US 6,245,595 B1 · Techniques for wafer level molding of underfill encapsulant

Abstract

A method and apparatus for forming a layer of underfill encapsulant on an integrated circuit located on a wafer are described. As a flip chip, the integrated circuit has electrically conductive pads, most of which have a solder ball attached thereto. Most of the solder balls have been flattened in order to provide an enlarged solder wetting area. A layer of underfill encapsulant is injected onto the integrated circuit under pressure to form a layer of underfill encapsulant that is then pre-cured. The integrated circuit is mounted to a substrate and the substrate and the integrated circuit are electrically coupled by a solder reflow operation which also finally cures the underfill encapsulant.

Claims15

Dependent claims

A method for forming a layer of underfill encapsulant on an integrated circuit having an active surface that includes electrically conductive pads selected ones of which have a solder ball bonded thereto, comprising:

flattening a portion of most of the solder balls;
forming a pre-cured layer of underfill encapsulant having a dual stage curing chemistry that includes a pre-cure stage and a final cure stage on the active surface of the integrated circuit such that the flattened solder ball is covered by the pre-cured encapsulant in such a manner that the flattened portion is substantially free of the pre-cured encapsulant;
and
reflowing the flattened solder balls so as to final cure the underfill encapsulant during the final cure stage such that there are substantially no voided regions between the substrate and the flip chip integrated circuit such that there is substantially no segregation of the layer of underfill encapsulant.

1 more element

A method for forming a layer of underfill encapsulant on an integrated circuit having an active surface that includes electrically conductive pads wherein selected ones of the pads each have a solder ball connected thereto, comprising:

flattening the solder balls by,
placing a resilient film coplanar to the active surface and in direct contact with the solder balls, and
providing a force to the resilient film normal to the active surface so that the solder balls are flattened in such a way that a solder ball footprint corresponding to the flattened solder balls is substantially enlarged thereby increasing available solder wetting area;
forming the layer of underfill encapsulant having a dual stage curing chemistry that includes a pre-cure stage and a final cure stage on the active surface of the integrated circuit, wherein a flattened portion of the solder balls remain substantially free of encapsulant by,
providing a mold having a mold cavity portion suitably arranged to receive the wafer and the encapsulant;
placing the wafer and the resilient film in the mold cavity portion;
clamping an enclosing portion of the mold on to the mold cavity portion thereby enclosing the wafer and the film in the mold cavity portion;
injecting the underfill encapsulant under pressure into the mold cavity, pre-curing the injected underfill encapsulant during the pre-cure stage;
and
reflowing the solder balls so as to final cure the underfill encapsulant during the final cure stage such that there are substantially no voided regions in the layer of underfill encapsulant.

7 more elements

Dependencies are inferred from the claim text.

Techniques for wafer level molding of underfill encapsulant

Life of this patent

Techniques for wafer level molding of underfill encapsulant

Life of this patent

Abstract

Claims15