The present invention generally relates to packaging of semiconductor chips. In one aspect it relates more particularly to an integrated circuit chip electrically connected to a substrate in a flip-chip configuration.
Integrated circuit devices typically include a semiconductor die or chip that is assembled in a package. A package typically has a substrate portion to which the chip is electrically connected. Usually the substrate is larger than the chip and has larger terminals, leads, or electrical contact points than that of the chip to allow for ease of electrically connecting a packaged chip onto a circuit board (e.g., while assembling a circuit board for a system). One such package configuration is a flip-chip package.
An example of a conventional flip-chip package 20 is shown in
One of the purposes of the underfill material 30 is to more evenly distribute the stresses between the chip 22 and the substrate 24 to reduce the stresses experienced by the solder bumps 26, solder bump joints, and/or circuitry layers above/below solder joints. Such stresses are caused, at least in part, by different coefficients of thermal expansion between the chip 22, the solder bumps 26, and the substrate 24 (i.e., coefficient of thermal expansion mismatch). The chip 22 is typically made from a silicon wafer, the substrate 24 is typically made from organic material having copper lines and vias extending therein, and the solder bumps 26 are typically made from a metal compound having a low melting point, for example. Thus, temperature changes (e.g., during use of the chip 22) cause stress on the solder bumps 26 connecting the chip 22 to the substrate 24 due to the different rates of material expansion/contraction between the chip 22 and the substrate 24. The underfill material 30 may also act as an adhesive to help retain the chip 22 to the substrate 24 so that not just the solder bumps 26 are holding the chip 22 in place. This further reduces stress exerted on the solder bumps 26.
Fabricating and assembling a flip-chip package using solder bumps, e.g., as described above, can be more expensive than other methods of attaching a chip to a substrate (e.g., wire bonding). Also, connections using wire bonding are often stronger than connections using solder bumps. Furthermore, many manufacturing facilities already have wire bonding machines. However, wire bonding is typically not suited for flip-chip configurations, and flip-chip configurations are preferred by some manufacturers. Hence, it would be desirable to provide a way to attach a chip to a substrate using a wire bonding machine and using a flip-chip configuration.
The problems and needs outlined above may be addressed by embodiments of the present invention. In accordance with one aspect of the present invention, a semiconductor chip package is provided, which includes an integrated circuit chip, a chip contact pad, a stud, and a substrate. The chip contact pad is formed on a first side of the chip. The stud is formed on the chip contact pad. The stud is formed from wire using a wire bonding machine. The stud has a partially squashed ball portion bonded to the chip contact pad. The stud also has an elongated portion extending from the partially squashed ball portion. The substrate includes a first layer of insulating material, a well, a first conductive material, and a second layer. The first layer of insulating material is on a first side of the substrate. The well is formed in the first layer and opens to the first side of the substrate. The well has a bottom. The first conductive material at least partially fills the well. The second layer has conductive trace lines formed therein. The first conductive material is electrically connected to at least one of the trace lines. The stud is partially embedded in the first conductive material to form an electrical connection between the chip and the substrate. The first side of the chip faces the first side of the substrate.
In accordance with another aspect of the present invention, a method of forming a semiconductor chip package is provided. This method includes the following steps described in this paragraph, and the order of steps may vary. An integrated circuit chip is provided. The chip includes a chip contact pad formed on a first side of the chip. A wire in a wire bonding machine is provided. A tip of the wire has a ball-shaped portion. The ball-shaped portion of the wire is wire bonded onto the chip contact pad with the wire bonding machine. The ball-shaped portion becomes partially squashed during the wire bonding. The wire is severed so that an elongated portion of the wire remains extending from the partially squashed ball-shaped portion to form a stud. A substrate is provided, which includes a first layer of insulating material, a well, a first conductive material, and a second layer. The first layer of insulating material is on a first side of the substrate. The well is formed in the first layer and opens to the first side of the substrate. The well has a bottom. The first conductive material at least partially fills the well. A second layer has conductive trace lines formed therein. The first conductive material is electrically connected to at least one of the trace lines. At least part of the elongated portion of the stud is immersed into the first conductive material to form an electrical connection between the chip and the substrate. The first side of the chip faces the first side of the substrate.
In accordance with still another aspect of the present invention, a semiconductor chip package is provided, which includes an integrated circuit chip, a chip contact pad, a stud, a substrate, and a support member. The chip contact pad is formed on a first side of the chip. The stud is formed on the chip contact pad. The stud is formed from wire using a wire bonding machine. The stud has a partially squashed ball portion bonded to the chip contact pad. The stud has an elongated portion extending from the partially squashed ball portion. The substrate includes a first layer of insulating material, a well, a conductive liner, a first conductive material, and a second layer. The first layer of insulating material is on a first side of the substrate. The well is formed in the first layer and opens to the first side of the substrate. The well has a bottom. The conductive liner at least partially lines the well. The first conductive material at least partially fills the well. The second layer has conductive trace lines formed therein. The first conductive material is electrically connected to at least one of the trace lines via the conductive liner. The support member extends from the first layer of the substrate between the chip and the substrate. The stud is partially embedded in the first conductive material to form an electrical connection between the chip and the substrate. The first side of the chip faces the first side of the substrate. The chip is at least partially supported by the support member.
The foregoing has outlined rather broadly features of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures or processes for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.
The following is a brief description of the drawings, which illustrate exemplary embodiments of the present invention and in which:
Referring now to the drawings, wherein like reference numbers are used herein to designate like elements throughout the various views, illustrative embodiments of the present invention are shown and described. The figures are not necessarily drawn to scale, and in some instances the drawings have been exaggerated and/or simplified in places for illustrative purposes only. One of ordinary skill in the art will appreciate the many possible applications and variations of the present invention based on the following illustrative embodiments of the present invention.
The chip contact pads 42 may be made from any of a variety of appropriate materials, including for example (but not limited to): gold, aluminum, nickel, palladium, tungsten, copper, or combinations thereof. The studs 40 may be made from any of a variety of appropriate materials, including for example (but not limited to): gold, silver, copper, aluminum, lead, tin, solder, and combinations thereof. The wire bonding machine may or may not use ultrasonic energy during bonding, depending at least in part on the materials used for the chip contact pads 42 and the studs 40. It is preferred to use gold for the studs 40 and gold as the outermost, exposed material of the chip contact pads 42 (hence, a gold-on-gold bond). One of the advantages of using gold for the studs 40 and for the chip contact pads 42 is that it may allow for bonding at a low capillary force; thus lowering stress exerted on the chip 22 during bonding. Reducing stress on the chip is becoming a growing concern where weak, low-k dielectric materials are implemented into the chip structure, for example. Also, a gold-on-gold bond may reduce or eliminate the need for using ultrasonic energy and/or high heat to form a bond between the stud 40 and the chip contact pad 42, which may be advantageous as well. In such case where the forces exerted on the chip 22 are lowered by using a gold-on-gold bond, for example, the chip contact pads 42 may be moved to the center portion of the chip 22 as well; thus allowing for the placement of chip contact pads 42 at any or almost any location on the first chip side 44. This may allow for more chip contact pads 42 per chip area and/or more spacing between chip contact pads 42.
Still referring to
The first substrate layer 48 may be made from any of a variety of appropriate materials, including (but not limited to): organic material (e.g., as commonly used in low cost substrates), ceramic, fiberglass, resin, plastic, polymer, and combinations thereof, for example. The conductive liner 58 may be made from any of a variety of appropriate materials, including (but not limited to): metal, copper, silver, gold, aluminum, titanium, tantalum, or combinations thereof, for example. In a preferred embodiment, the wells 54 have copper liners 58 formed in organic material.
The first conductive material 60 may be any of a variety of appropriate materials, including (but not limited to): solder, conductive adhesive, conductive polymer material, metal compounds, or combinations thereof, for example. If solder is used for the first conductive material 60, it is preferably an ultra fine pitch solder that allows for pitches of less than 90 μm, for example. Such ultra fine pitch solder may be screen printed into the wells 54, for example. Another preferred solder is Super Solder™ by Harima Chemicals, for example, which may have a combination of Sn, RCOO—Cu, RCOO—Ag, and flux. However, many other suitable solders are available and may be used as well in an embodiment of the present invention. In
When a conductive adhesive (e.g., conductive polymer material) is used as the first conductive material 60 in the wells 54, it may be deposited into the wells 54 and the studs 40 may be inserted into the first conductive material 60 before it cures, for example. In a preferred embodiment, the conductive adhesive may remain uncured until it is treated to provide adequate time for inserting the studs 40. Such treatment may be provided by heating the adhesive, adding another chemical to the adhesive, exposing the adhesive to a certain gas or environment, or combinations thereof, for example. However, in other embodiments, the conductive adhesive may simply cure over a specified period of time. In a preferred embodiment, the conductive adhesive retains a specified amount of flexibility after curing to allow for slight movement of the stud 40 therein for relieving thermal stress, for example. In this or other embodiments, including those with solder as the first conductive material 60, flexibility may also be provided by the wire stud 46 spanning between chip 22 and substrate 24. The flexibility provides relief from stress caused by, e.g., different CTE of the different materials.
When the chip 22 is electrically connected to the substrate 24, as shown in
After the studs 40 are inserted into the first conductive material 60 in the wells 54 to interconnect the chip 22 with substrate 24, an underfill material 30 may be provided between the chip 22 and the substrate 24, as shown in
Focusing again on the substrate 24 of
Vias 68 extend to a second side 70 of the substrate 24 and are filled with a second conductive material 72 (e.g., metal), as shown in
Note in
Referring to
In a preferred configuration, the chip 22 rests on and is at least partially supported by the support members 80. The use of support members 80 may be advantageous in situations where the studs 40 do not have consistent lengths. Also, by having the chip 22 rest on the support members 80, the distance between the chip 22 and the substrate 24 may be controlled by the height of the support members 80 rather than the length of the studs 40 and/or the depth of the wells 54. In the example configuration shown in
The height of, shape of, placement, and number of support members 80 may vary for an embodiment of the present invention, as will be apparent to one of ordinary skill in the art. Also, the depth and width (or diameter) of the wells 54 may vary for an embodiment of the present invention. The cross-section shape of the wells 54 may vary as well, including (but not limited to) being round, oval, square, rectangular, or with rounded corners, for example. And, the wire size, ball size, and stud length may vary for an embodiment of the present invention. As an illustrative example, the wells 54 may have a depth of about 200 μm and a diameter of about 100 μm, the studs 40 may have a wire diameter of about 50 μm and a length of about 300 μm, and the support members 80 may have a height of about 150 μm. Hence, in such case, the space between the first chip side 44 and the first substrate side 50 may be about 150 μm, the tips of the studs 40 will be about 50 μm from the well bottoms 56, and about 150 μm of the stud 40 will be immersed in the first conductive material 60 (assuming the first conductive material 60 fills the well 54 after inserting the stud 40 in this case), for example. In other embodiments, the studs 40 may have a length between about 50 μm and about 300 μm, and a wire diameter between about 30 μm and about 50 μm, for example.
The amount of the first conductive material 60 placed in each well 54 may vary so that the well 54 is filled, less than filled, or overflowing with the first conductive material 60 after inserting the studs 40. If the first conductive material 60 overfills a well 54 after the insertion of a stud 40 therein, the excess portions of the first conductive material 60 will likely cling to and wet the sides of the studs 40 above the substrate surface; thus avoiding the spreading of excess portions of the first conductive material 60 across the first substrate side 50, which may cause unwanted shorts. Thus, such wetting or wicking of the studs 40 with the first conductive material 60 may be a preferred and advantageous feature of the design. In a preferred embodiment, the first conductive material 60 just fills a well 54 (see e.g.,
In a preferred embodiment, the substrate may be a low-cost substrate 24 having a thicker first substrate layer 48 with wells 54 formed therein (e.g., rather than bump landing pads), for example. Also, in other embodiments (not shown), the substrate 24 may be a configuration other than BGA, such as a substrate 24 with pins or leads extending from the second substrate side 70 or other sides of the substrate, for example. With the benefit of this disclosure, one of ordinary skill in the art will realize many other variations on substrate designs while incorporating the bottomed wells 54 for an embodiment of the present invention. Also, the placement and array configuration of the chip contact pads 42 (and thus the studs 40) on a chip 22 may vary widely, as will be apparent to one of ordinary skill in the art.
Another advantage of an embodiment of the present invention is that stress concentrations normally experienced at solder joints in a solder bump configuration (see e.g.,
Although studs 46 are shown and described in the first and second embodiments of
Although embodiments of the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods, and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed, that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.