1. Field of the Invention
The present invention generally relates to the field of semiconductors. In particular, the present invention relates to an improved method of assembling a true Chip Scale Package (CSP).
2. Discussion of Related Art
Semiconductors are materials that have characteristics of insulators and conductors. In today's technology, semiconductor materials have become extremely important as the basis for transistors, diodes, and other solid-state devices. Semiconductors are usually made from germanium or silicon, but selenium and copper oxide, as well as other materials are also used. When properly made, semiconductors will conduct electricity in one direction better than they will in the other direction.
Semiconductor devices and integrated circuits (ICs) are made up of components such as transistors, and diodes, and elements such as resistors and capacitors linked together by conductive connections to form one or more functional circuits. Interconnects on an IC chip serve the same function as the wiring in a conventional circuit.
Wire bonding is a method used to attach very fine metal wire to semiconductor components in order to interconnect the components with each other or with package leads. One problem encountered with wire bonds is the parasitic inductance that arises, which is based on the size and length of the wire carrying electricity to the components. Wire bonds are also fragile and have limited current carrying capacity.
A flip chip is a leadless monolithic structure, containing circuit elements, which is designed to connect electrically and mechanically to a hybrid circuit. Such a connection may be, but is not limited to, a structure such as a plurality of bumps, which are covered with a conductive bonding agent and are formed on the front-side planar face of the flip chip. In one conventional flip chip mounting technique for integrated circuits, an IC chip is placed front face-down on a mounting base layer element (a substrate) and is connected to wire patterns on the base layer element using the bumps as electrical contacts and the conductive bonding agent as an adhesive. Because the flip chip mounting technique can bond a chip to a base layer element over a much shorter distance than wire bonding, an effect of parasitic inductance can be reduced. Also, the thicker bumps are less fragile than wires and can conduct greater amounts of current. Therefore, some flip chips can be mounted onto a circuit base layer element with limited or even no need for wire bonding, and flip-chip mounting is drawing increasing interest as a mounting technique for high-frequency integrated circuits.
Conventional methods of producing flip-chip packages, however, involve singulating an individual IC chip from a wafer and attaching the singulated IC chip to a substrate. Such individual processing of a single IC chip is highly inefficient in that it is both time-consuming and expensive. Another problem associated with the individual mounting of a singulated IC chip onto a substrate is the difficulty of balancing a single IC chip (e.g. IC chip 10) on a single, central row of bumps (e.g. bumps 5), as illustrated in
A method of producing a chip scale package according to an exemplary embodiment of the present invention comprises mounting all array of two or more IC chips on a substrate and dicing the array, attached to the substrate, into individual chip scale packages, each package including only one IC chip.
A method of producing a chip scale package according to another exemplary embodiment of the present invention comprises providing a wafer and dicing the wafer. The wafer comprises a plurality of IC chips and the wafer is diced into a plurality of chip arrays, each array comprising two or more IC chips. After dicing, each array is mounted on a substrate and then each array, attached to the substrate, is diced into individual chip scale packages, such that each package includes only one IC chip. Each array may comprise a 2×2, 3×3, or 4×4 matrix of IC chips.
A method of producing a chip scale package according to yet another exemplary embodiment of the present invention comprises providing a wafer and dicing the wafer. The wafer comprises a plurality of IC chips, each comprising a plurality of bond pads aligned on an upper surface of the IC chip and a plurality of conductive bumps formed on the plurality of bond pads. The wafer is diced into a plurality of chip arrays, each array comprising two or more IC chips. Each array is then dipped in flux material so that flux material adheres to the bumps on the IC chips of the array. Each array is then mounted on a substrate so that the bumps align with corresponding solder pad openings on an upper surface of the substrate, and so that the flux material adheres the bumps to the solder pad openings. Then, the IC chips of each array are reflowed, thereby melting the bumps and establishing a joint between the IC chips and the substrate. The IC chips, the bumps, and the substrate are then cleaned to remove residual flux material. Then, the IC chips are under fill encapsulated by injecting encapsulation material into a gap between the IC chips and the substrate. Solder balls are formed on the under surface of the substrate, conductively connected to the bumps. The array, attached to the substrate, is diced into individual chip scale packages, each package comprising only one IC chip.
These and other features, aspects, and advantages of the present invention will become better understood % with reference to the following description, amended claims, and accompanying drawings, which should not be read to limit the invention in any way, in which:
The present invention will be explained in further detail with reference to the accompanying drawings.
Each IC chip 101, includes a plurality of bond pads 104 formed on a top surface thereof. The bond pads 104 are applied through conventional printed circuit technology. A bump 105 (see e.g.,
According to the present exemplary embodiment, a conventional IC wafer, such as wafer 200, is diced into separate chip arrays, (Step S2,
After a wafer is diced into chip arrays 100, each array, comprising multiple IC chips, is fixedly attached to a substrate 300, as illustrated in
In order to attach the array 100 to the substrate 300, the array 100 is first flipped so that the bumps 105, disposed on the upper face of the IC chip can be mounted to the substrate 300 (Step S3,
As shown in
After the array 100 is flipped, the array 100 is dipped in a flux material such that some amount of the flux adheres to the bumps 105. (Step S4,
Once the array 100 is mounted on the substrate 300 (Step S5,
After the flux cleaning step, the IC chips 101A, 101B, 101C, and 101D of the array 100 are encapsulated, as shown in
The under fill encapsulation material 401 strengthens the final package, helping to prevent shock or vibration from causing the electrical connections between the IC chips 101A, 101B, 101C, and 101D and the substrate 300 to sever. The under fill encapsulation also protects the connections from moisture and contamination.
The under fill encapsulation material 401 is dispensed at one or more sides of the gap between the IC chips 101A, 101B, 101C, and 101D and the substrate 300 and flows by capillary action until it fills the gap and surrounds each of the bumps 105. A low-viscosity under fill encapsulation material can be used to flow into the gap quickly enough to allow for high-speed production.
As an alternative to under fill encapsulation materials, and as would be understood by one of still in the art, a molding compound that is adapted to flow easily can be applied directly around the array 100 in
Once the array 100 and the substrate 300 have been encapsulated, as described above, solder balls 501, as shown in
After the solder balls 501 have been formed on the under surface of the substrate, the entire arrangement is subjected to saw singulation, isolating each of the IC chips 101A, 101B, 101C, and 101D, as shown in
An exemplary individual true CSP, resultant from the above-described process, is illustrated in
Although the above exemplary embodiments and aspects of the present invention have been described, it will be understood by those skilled in the art that the present invention should not be limited to the described exemplary embodiments, but that various changes and modifications can be made within the spirit and scope of the present invention.
This application claims the benefit of the co-pending U.S. Provisional Application No. 60/526,082 filed on Dec. 2, 2003, and incorporated herein by reference.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/IB2004/004394 | 12/2/2004 | WO | 00 | 8/14/2008 |
Number | Date | Country | |
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60526082 | Dec 2003 | US |