Semiconductor device manufacturing: process – Packaging or treatment of packaged semiconductor – Encapsulating
Reexamination Certificate
2001-08-30
2003-04-22
Cuneo, Kamand (Department: 2827)
Semiconductor device manufacturing: process
Packaging or treatment of packaged semiconductor
Encapsulating
C438S108000, C438S124000, C438S126000, C438S613000, C228S180100, C228S180210, C228S180220
Reexamination Certificate
active
06551863
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to semiconductor manufacturing, and more specifically to methods and apparatus for applying an encapsulant to a flip chip.
Typically, in flip chip packaging, one or more integrated circuits (IC) chips are mounted on a substrate to form an electronic substrate. Solder balls (also known as solder bumps), which are mounted on the electrical connection pads of the flip chip are aligned with the corresponding electrical connection pads on the substrate. The flip chip and the substrate are then heated to cause the solder to melt (or “reflow”) and wet the electrical connection pads of the substrate. The substrate and flip chip are then cooled to solidify the solder thereby forming the desired electrical connections.
As with any IC chip mounted on a substrate surface, differences in the thermal expansion coefficients between the chip and the surface can cause stress and fatigue in these connections as the substrate is subjected to further heat/cool cycles during subsequent processing. A common method of reducing this stress, and providing better adhesion, is to fill the gap between the chip and the mounting surface with a suitable polymeric underfill resin.
Furthermore, IC chips mounted on substrates are frequently coated with a polymeric encapsulation resin to protect the IC chip from outside contamination and mechanical stress. However, separate application of the underfill and the encapsulant requires extra process steps. Additionally, the encapsulant may not be compatible with the underfill.
Known methods which apply the underfill and the encapsulant simultaneously typically require extra steps for masking the electrical contact area of the solder balls or else require etching steps to remove encapsulant from these areas. Therefore, a method for simultaneously underfilling and encapsulating an IC chip without masking or removal steps is desirable.
BRIEF SUMMARY OF THE INVENTION
In one preferred embodiment, the invention is a method for encapsulating and underfilling a lip chip, the method comprising the steps of: providing a flip chip having projections of conductive material on one side of the flip chip, the projections having a proximate end attached to the flip chip and a distal end opposite the proximate end; immersing the flip chip in a polymer bath, wherein the polymer bath covers the flip chip and part of the projections up to a point between the proximate end of the projection and the distal end of the projection; removing the flip chip from the polymer bath such that a coating of polymer adheres to the flip chip and the part of the projections covered by the polymer bath to form a coated flip chip having the distal ends of the projections uncoated; applying ultraviolet light or heat (e.g., IR radiation) to the coated flip chip such that an outer layer of the coating cures to form a skin-cured flip chip; placing the skin-cured flip chip on a substrate board to form an assembly; heating the assembly such that: (i) the conductive material forms an electrical junction between the flip chip and the substrate; (ii) the polymer from the polymer coating on the flip chip underfills and encapsulates the flip chip; and, (iii) the polymer from the coating cures.
In another preferred embodiment, the invention is a method for encapsulating and underfilling a flip chip, the method comprising the steps of: providing a flip chip having projections of conductive material on one side of the flip chip, the projections having a proximate end attached to the flip chip and a distal end opposite the proximate end; providing a pick-up tip, the pick-up tip having indentations corresponding to the projections on the flip chip, wherein the indentations are in fluid communication with a vacuum source; positioning the pick-up tip in contact with, or close proximity to, the flip chip such that the indentations align with and partially cover the projections; applying a vacuum through the indentations such that the flip chip is secured to the pick-up tip; repositioning the pick-up tip such that the flip chip secured to the pick-up tip is immersed in a polymer bath, wherein the polymer bath covers the flip chip and part of the projections up to a point between the proximate end of the projection and the distal end of the projection; removing the flip chip from the polymer bath such that a coating of polymer adheres to the flip chip and the part of the projections covered by the polymer bath to form a coated flip chip having the distal ends of the projections are uncoated; applying ultraviolet light or heat (e.g., IR radiation) to the coated flip chip such that an outer layer of the coating cures to form a skin-cured flip chip; releasing the skin-cured flip chip from the pick-up tip; placing the skin-cured flip chip on a substrate board to form an assembly; heating the assembly such that: (i) the conductive material forms an electrical junction between the flip chip and the substrate; (ii) the polymer from the polymer coating on the flip chip underfills and encapsulates the flip chip; and, (iii) the polymer from the coating cures.
In another preferred embodiment, the invention is a method for encapsulating and underfilling a flip chip, the method comprising the steps of: providing a flip chip having projections of conductive material on one side of the flip chip, the projections having a proximate end attached to the flip chip and a distal end opposite the proximate end; securing the flip chip to a pick-up tip by means of a vacuum; positioning the pick-up tip such that the flip chip attached thereto is partially immersed in a polymer bath to a level between the proximate end and the distal end of the projections; removing the flip chip from the polymer bath such that a coating of the polymer remains in contact with the flip chip such that the distal ends of the projections are uncoated; applying ultraviolet light or heat (e.g., IR radiation) to the coated flip chip such that an outer layer of the coating cures to form a skin-cured flip chip; releasing the skin-cured flip chip from the pick-up tip; placing the skin-cured flip chip on a substrate board to form an assembly; heating the assembly such that: (i) the conductive material forms an electrical junction between the flip chip and the substrate; (ii) the polymer from the polymer coating on the flip chip underfills and encapsulates the flip chip; and, (iii) the polymer from the coating cures.
In another preferred embodiment, the invention is a method for encapsulating and underfilling a flip chip, the method comprising the steps of: providing a flip chip having projections of conductive material on one side of the flip chip, the projections having a proximate end attached to the flip chip and a distal end opposite the proximate end; providing a pick-up tip, the pick-up tip having indentations corresponding to the projections on the flip chip, the indentations in fluid communication with a vacuum source; positioning the pick-up tip in contact with, or close proximity to, the flip chip such that the indentations align with and partially cover the solder balls; applying a vacuum through the indentations such that the flip chip is secured to the pick-up tip; repositioning the pick-up tip such that the flip chip secured to the pick-up tip is partially immersed in a polymer bath such that the immersed chip is fully wetted by the polymer, the flip chip being immersed to a point such that the pick-up tip and the distal ends of the projections extend above the polymer bath, wherein the polymer bath is ultrasonically vibrated and the polymer bath has a viscosity sufficiently high such that the polymer bath is not pulled above the desired immersion point by the vacuum securing the flip chip to the pick-up tip; removing the flip chip from the polymer bath such that a coating of the polymer remains in contact with the flip chip such that the distal ends of the projections are uncoated; applying ultraviolet light or heat (e.g., IR radiation) to the coated flip chip such that an outer layer of the coating cu
Jiang Tongbi
Johnson Farrah J.
Cuneo Kamand
Micro)n Technology, Inc.
Whyte Hirschboeck Dudek SC
Zarneke David A.
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