Semiconductor device manufacturing: process – Packaging or treatment of packaged semiconductor
Reexamination Certificate
2000-01-19
2001-05-01
Niebling, John F. (Department: 2812)
Semiconductor device manufacturing: process
Packaging or treatment of packaged semiconductor
C438S126000, C438S127000
Reexamination Certificate
active
06225144
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a method and machine for underfilling an assembly to form semiconductor package. The invention is particularly useful for, but not necessarily limited to, flip chip semiconductor packages having an inverted die mounted to a substrate.
BACKGROUND ART
Ever increasing requirements for reducing the size of packaged semiconductor devices has led to the development of several different types of semiconductor packages. Generally speaking, reduced sizes of semiconductor devices use an inverted die that is directly attached to a substrate to thereby increase the density of external connections that are provided within the perimeter of the package.
One such package is known as a flip chip semiconductor package and sometimes comprises a flexible tape substrate with a pattern of runners with corresponding outer portions that are made available for interconnection to, for example, a printed circuit board. An inverted die is mounted to the substrate and the runners are soldered to pads on the die. With this package a relatively high density of runners can. be formed on the flexible substrate to provide a higher density of external connections. The flip chip semiconductor package with a flexible tape substrate is becoming a popular alternative to the conventional more rigid substrate packages. Currently, flip chip semiconductor packages are manufactured such that after the die is mounted to the flexible substrate to form an assembly. The assembly is preheated then an underfill material is dispensed onto the assembly in a heated dispensing zone. The underfill then starts to flow into a gap between the substrate and die. The assembly remains stationary in the dispensing zone to allow the underfill to be drawn into the gap by the effects of capillary action. The assembly is then conveyed to a cooling zone heat is removed from the assembly and the underfill material at least partially solidifies. The assembly is later reheated to cure the underfill and form the completed semiconductor package. However, in order to increase production rates, the assembly may be prematurely removed from the heated dispensing zone and the underfill may not have been completely drawn into the gap by the effects of capillary action. Alternatively, if the assembly is kept stationary in the heated dispensing zone until the underfill have been completely drawn into the gap, then this unnecessarily increases the time to manufacture underfilled semiconductor packages.
SUMMARY OF THE INVENTION
It is an object of the present invention to overcome or alleviate at least one of the problems associated with prior art underfilling of assemblies to form semiconductor packages.
According to one aspect of the invention there is provided a method for underfilling an assembly to form a semiconductor package, the method including the steps of:
preheating an assembly including a substrate with at least one semiconductor die mounted thereto;
dispensing an underfill material onto the substrate whilst heating the assembly, said heating providing for said underfill to flow into a gap between said substrate and said semiconductor die; and
postheating the assembly immediately after said dispensing to provide for a continuous flow of said underfill into said gap, wherein during said step of postheating said assembly continuously moves along a conveyor.
Suitably, said step of postheating may be for a duration of at (east thirty seconds after the step of dispensing.
Preferably, the method may further include the steps of:
cooling said underfill; and subsequent curing of said underfill.
Preferably, said method may be further characterised by said substrate being a flexible tape.
Suitably, said method may be further characterised by said assembly continuously moving during the steps of preheating, dispensing and postheating.
Preferably, said method may be further characterised by said assembly continuously moving during the steps of cooling and subsequent curing.
According to another aspect of the invention there is provided a machine for underfilling an assembly to form a semiconductor package, said machine including:
a conveyor for continuously conveying an assembly past at least some zones of said machine, said assembly including a substrate with at least one semiconductor die mounted thereto;
a preheating zone;
a dispensing zone for dispensing an underfill material onto the substrate whilst heating the assembly, said heating providing for said underfill to flow into a gap between said substrate and said semiconductor die; and
a postheating zone for postheating the assembly immediately after said dispensing to provide for a continuous flow of said underfill into said gap.
Suitably, said postheating zone and conveyor may provide for a postheating duration of at least thirty seconds after the step of dispensing, said postheating being at substantially the same temperature as that of said dispensing zone.
Preferably, the machine may be coupled by said conveyor to a cooling zone and subsequent curing zone for curing of said underfill material.
REFERENCES:
patent: 5784261 (1998-07-01), Pedder
patent: 5930598 (1999-07-01), Wille et al.
patent: 6015722 (1999-07-01), Banks et al.
patent: 6046076 (2000-04-01), Mitchell et al.
Chua Han Yang
How James Boon Hua
Ling Nee Seng
Yuan Peter Zhihua
Jones Josetta I.
Macnak Philip P.
Motorola Inc.
Niebling John F.
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