Method of underfilling an integrated circuit chip

Details Method of underfilling an integrated circuit chip Method of underfilling an integrated circuit chip

1999-05-17

2002-12-17

Ortiz, Angela (Department: 1732)

Plastic and nonmetallic article shaping or treating: processes

Mechanical shaping or molding to form or reform shaped article

To produce composite, plural part or multilayered article

C264S272170, C029S841000, C425S116000, C425S812000

Reexamination Certificate

active

06495083

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to an integrated circuit chip mounting system and more particularly, to an integrated circuit chip package and a method of electrically connecting and mounting integrated circuit chips to a substrate.
BACKGROUND OF THE INVENTION
Flip chip technology is well known in the art for electrically connecting an integrated circuit chip to an integrated circuit substrate or package. Formation of one type of flip chip involves forming solder bumps on electrical interconnection pads on the active or front side of a semiconductor chip. The chip with solder bumps is then inverted onto a laminate substrate with the solder bumps aligned with metal circuits provided on the substrate. The solder bumps on the chip are then soldered to the metal pads on the substrate by melting the solder in a reflow furnace. A solder joint is formed by the reflowing of the solder between the semiconductor chip and the substrate. After the chip has been attached to the substrate by the reflow soldering process, narrow gaps are present between the solder bumps.
The substrate is typically comprised of a ceramic material or a polymer composite laminate, while the chip is formed of silicon. Due to these different materials, there is a mismatch in the coefficient of thermal expansion between the semiconductor chip and the substrate on which the chip is mounted. During temperature cycling the semiconductor chip and substrate expand and contract at differing rates. Accordingly, the soldered joints between the semiconductor chip and the substrate will have a tendency to fail because of the coefficient of thermal expansion mismatch. In addition, because of the very small size of the solder joints, the joints are subject to failures.
The strength of the solder joints between the integrated circuit chip and the substrate are typically enhanced by underfilling the space between the semiconductor chip and the substrate and around the solder joints. The underfill material is typically a polymer adhesive which reduces stress on the solder joints.
The conventional method of underfilling includes dispensing the underfill material in a fillet or bead extending along two or more edges of the chip and allowing the underfill material to flow by capillary action under the chip to fill all the gaps between the semiconductor chip and the substrate. The solder bumps create a very narrow gap between the semiconductor chip and the substrate which is about 0.002-0.005 inches (0.051-0.127 mnm). Therefore, the underfill material which is capable of flowing through these narrow gaps contains only a small amount of filler material because the filler material will prevent the underfill material from flowing easily into the gaps. This type of underfill material with a low amount of filler material has an extremely high mismatch of coefficient of thermal expansion with the semiconductor chip, the solder bumps, and the substrate. Accordingly, it would be desirable to use an underfill material having more filler and thus, less of a thermal expansion coefficient mismatch with the substrate and chip.
An example of an integrated circuit chip
100
which has been attached to a substrate
102
by solder balls
104
and underfilled by a conventional method is illustrated if
FIGS. 3 and 3
a
. The underfill material
106
has been drawn into the spaces between the solder balls
104
by capillary action to fill the air spaces between the integrated circuit chip
100
and the substrate
102
.
The use of capillary action to suck the underfill material into the gap between the integrated circuit chip and the substrate takes between 5 and 20 minutes, depending on many factors including the size of the chip and the underfill material used. Another drawback of the conventional underfilling method is the occurrence of voids in the underfilling material.
Accordingly, a need exists for an underfilling method for completely filling the spaces between an integrated circuit chip and a substrate which can reliably underfill at a faster rate than known methods.
SUMMARY OF THE INVENTION
An integrated circuit chip package according to one aspect of the present invention includes an integrated circuit chip having an active surface with interconnection pads disposed thereon, and a substrate having a first surface with bonding pads substantially corresponding to the interconnection pads of the integrated circuit chip and a second side having a plurality of solder pads electrically interconnected with the bonding pads. A vent hole extends from the first side to the second side of the substrate, and is positioned beneath the integrated circuit chip when the chip is mounted on the substrate. A plurality of solder bumps electrically connect the interconnection pads of the integrated circuit chip with the bonding pads on the first side of the substrate. A molded underfill material is molded around the integrated circuit chip. The molded underfill material surrounds the solder bumps between the integrated circuit chip and the substrate and extends into the vent hole in the substrate.
A further aspect of the present invention relates to a method of underfilling an integrated circuit chip which has been electrically interconnected to a substrate. The method includes the steps of placing the integrated circuit chip and substrate within a mold cavity, injecting a mold compound into the mold cavity, underfilling a space between the integrated circuit chip and the substrate with the mold compound by the pressure of injection of the mold compound into the mold cavity, and allowing air to escape from between the integrated circuit chip and the substrate during underfilling through a vent in the substrate.
The present invention addresses the deficiencies of known underfilling methods by underfilling faster and more reliably than the known methods. In addition, the present invention forms an encapsulated integrated circuit chip package and performs underfilling in the same step.


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