Schottky Diode Device with Aluminum Pickup of Backside Cathode
An integrated circuit package includes a semiconductor chip having a passivation layer forming the top surface of the semiconductor chip and a metal pad formed on the passivation layer and a discrete electronic device having a first terminal formed on a first surface and a second terminal formed on a second surface opposite the first surface of the discrete electronic device where the first surface of the discrete electronic device is attached to the metal pad using a conductive adhesive structure. The semiconductor chip and the discrete electronic device are encapsulated in an encapsulation material. An electrical connection is formed between the metal pad and one of a bond pad of the semiconductor chip or a package post of the integrated circuit package. In one embodiment, the metal pad is an aluminum pad and a metal line connects the metal pad to a bond pad of the semiconductor chip.
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This application is a divisional of application Ser. No. 11/087,913, filed Mar. 22, 2005, entitled “Schottky Diode Device with Aluminum Pickup of Backside Cathode” of the same inventors hereof, which application is incorporated herein by reference in its entirety.
FIELD OF THE INVENTIONThe invention relates to discrete Schottky diode devices with backside cathode contact and, in particular, to a method for providing backside pickup of the backside cathode contact of a discrete Schottky diode device.
DESCRIPTION OF THE RELATED ART Step-up converters, or boost converters, are known in the art and operate by taking a DC input voltage and regulating a higher DC output voltage.
Most boost converters require a Schottky diode coupled between the switch output node SW terminal of the boost converter IC and the output voltage VOUT node. In most cases, a user needs to buy a discrete Schottky diode separate from the boost converter IC and assembles the discrete Schottky diode on the PC board next to the boost converter IC. Having to use a discrete Schottky diode is undesirable as it is expensive and awkward for the user. The discrete Schottky diode also takes up valuable PC board space.
In portable applications, there is a trend by manufacturers (such as cell phone manufacturers) to minimize the number of components on their PC board. One solution to reducing component count is to integrate the discrete Schottky diode on-chip but an on-chip Schottky diode is not a very cost-effective solution. This is because building a discrete Schottky diode only requires a low number of processing steps but if the Schottky diode is built within the IC chip the a large number of additional processing steps is required and large silicon area is needed to implement the integrated Schottky diode. Therefore the cost of integrating the Schottky diode is inflated.
SUMMARY OF THE INVENTIONAccording to one embodiment of the present invention, a method for forming an integrated circuit package where the integrated circuit package includes a semiconductor chip having a passivation layer and a discrete electronic device is disclosed. The discrete electronic device includes a first terminal formed on a first surface and a second terminal formed on a second surface opposite the first surface of the discrete electronic device. At least one of the first and second terminals of the discrete electronic device is electrically coupled to the semiconductor chip. The method includes forming a metal pad on the top surface of the passivation layer of the semiconductor chip, attaching the first surface of the discrete electronic device to the metal pad using a conductive adhesive structure to form an electrical connection between the first terminal of the discrete electronic device and the metal pad, forming an electrical connection from the metal pad to one of a bond pad of the semiconductor chip or a package post of the integrated circuit package, and encapsulating the semiconductor chip and the discrete electronic device to form the integrated circuit package.
In one embodiment, the metal pad is an aluminum pad and the conductive adhesive structure includes a conductive epoxy.
According to another aspect of the present invention, an integrated circuit package includes a semiconductor chip having a passivation layer forming the top surface of the semiconductor chip and a metal pad formed on the passivation layer and a discrete electronic device having a first terminal formed on a first surface and a second terminal formed on a second surface opposite the first surface of the discrete electronic device where the first surface of the discrete electronic device is attached to the metal pad using a conductive adhesive structure. The semiconductor chip and the discrete electronic device are encapsulated in an encapsulation material. An electrical connection is formed between the metal pad and one of a bond pad of the semiconductor chip or a package post of the integrated circuit package.
In one embodiment, the metal pad is an aluminum pad and a metal line connects the metal pad to a bond pad of the semiconductor chip.
The present invention is better understood upon consideration of the detailed description below and the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
In accordance with the principles of the present invention, a method for forming a chip-on-chip integrated circuit package uses a metal pickup formed on the top surface of a semiconductor chip for electrically contacting the backside electrode of a discrete electronic device. The electronic device can thus be mounted on the top surface of the semiconductor chip so that each can be electrically coupled to the other while being assembled inside the same integrated circuit package. The backside electrode of the discrete electronic device can be electrically coupled to the semiconductor chip or to a package post by the use of a bond wire attached to the metal pickup. The metal pickup is typically an aluminum pad formed on the topmost insulating layer of the semiconductor chip. The backside electrode of the discrete electronic device can also be electrically coupled to circuitry of the semiconductor chip by coupling the metal pickup to metal layers formed on semiconductor chip.
In one embodiment, the electronic device is mounted on an aluminum pad formed on the top surface of the semiconductor chip where the aluminum pad forms the metal pickup of the backside electrode of the electronic device. Electrical connection to the backside electrode of the electronic device can then be made through the aluminum pad. The method of the present invention simplifies the manufacturing of the discrete electronic devices by eliminating the need to bring the backside electrode to the top surface and enables compact assembly of discrete electronic device on a semiconductor chip by direct physical mounting and electrical connection of the electronic device on the semiconductor chip.
In one embodiment, the discrete electronic device is a discrete Schottky diode and the semiconductor chip is a boost converter integrated circuit. The discrete Schottky diode is mounted on the top surface of and above the passivation layer of the boost converter integrated circuit. An aluminum pad is formed on the top surface of the passivation layer of the boost converter integrated circuit to be used as the backside pickup of the backside cathode terminal of the discrete Schottky diode. The anode electrode of the Schottky diode is formed on the topside of the Schottky diode device and is electrically coupled to the switching output terminal (SW) of the boost converter integrated circuit, such as through a bond wire. The cathode electrode of the Schottky diode is formed on the backside of the Schottky diode device and is electrically connected to the aluminum pad functioning as the backside pickup of the cathode terminal. Electrical connection to the cathode terminal can then be made through the aluminum pad.
In this manner, the discrete Schottky diode is physically and electrically coupled to the boost converter integrated circuit to form a fully integrated boost converter IC package. Moreover, the discrete Schottky diode can be incorporated in a chip-on-chip fashion into the package of the boost converter IC without increasing the package size of the boost converter IC because the discrete Schottky diode merely occupies space previously occupied by the packaging encapsulation material.
In one embodiment, a bond wire is attached to the aluminum pad directly to provide the necessary electrical connection of the backside electrode. For example, the aluminum pad can be electrically connected to a package post through the bond wire. In another embodiment, the aluminum pad is electrically connected to a bonding pad on the semiconductor chip through a metal line. A bond wire can then be coupled to the bonding pad for providing electrical connection of the aluminum pad and the backside electrode of the Schottky diode. The topside anode terminal of the discrete Schottky diode can be electrically connected to either a bonding pad of the semiconductor chip or a package post of the package through a bond wire.
By using a backside cathode terminal, the size of the discrete Schottky diode device can be reduced as structures for bringing a cathode contact to the topside of the Schottky diode is eliminated. Such structures, such as N+ sinkers, require additional fabrication steps and additional silicon area. The discrete Schottky diode in accordance with the present invention can be made using very little silicon area and with fewer fabrication steps than an on-chip Schottky diode. In one embodiment, the discrete Schottky diode is formed using only eight masking steps.
Furthermore, by mounting the Schottky diode directly on the top surface of the boost converter integrated circuit to form a fully integrated IC package, a separate discrete component is eliminated in the application of the boost converter and valuable PC board space is saved. Furthermore, the aluminum pad is formed on the passivation layer of the boost converter integrated circuit and can be formed on top of active circuitry of the boost converter integrated circuit so that no additional silicon space is required for mounting the discrete Schottky diode device.
In the following description, the chip-on-chip integrated circuit packaging method is applied to a discrete Schottky diode device for connecting the backside cathode of the Schottky diode to an aluminum pick-up on a boost converter integrated circuit. The chip-on-chip integrated circuit packaging method can also be applied to other discrete electronic devices, particularly those that include a vertical device structure and therefore inherently incorporate device terminals on the backside of the electronic devices (hence, the backside electrodes). Instead of bringing an electrical connection of the backside electrode to the topside of such electronic device, backside pickup of the backside electrode can be advantageously exploited to reduce the size of the electronic device and to facilitate chip-on-chip mounting for components reduction. For example, the chip-on-chip integrated circuit packaging method can be applied to VDMOS devices for providing backside body pickup and NPN or PNP transistors for providing collector pickup. One of ordinary skill in the art, upon being apprised of the present invention, would appreciate that the chip-on-chip integrated circuit packaging method of the present invention can be applied to a wide range of electronic devices for utilizing the backside electrode pickup method to facilitate chip-on-chip mounting.
Furthermore, in the present description, the semiconductor chip or integrated circuit chip to which the discrete electronic device is attached can be any type of integrated circuit chips. The exact configuration or make up of the integrated circuit chip is not critical to the practice of the present invention.
In the embodiment shown in
Schottky diode 102 is a discrete device including an anode electrode on the top surface 102a of the diode and a cathode electrode formed on the bottom surface 102b. The backside of Schottky diode 102 is attached to metal pad 106, such as by conductive adhesive 104. Thus, metal pad 106 is electrically connected to the cathode terminal of Schottky diode 102 and forms the backside pickup of the cathode electrode of the Schottky diode. In other words, metal pad 106 functions as the backside cathode of the Schottky Diode.
Converter chip 108, with Schottky diode 102 mounted thereon, is attached by a die attach 112 to a die paddle 114 in a conventional manner.
By encapsulating Schottky diode 102 in the same package material 110 of converter chip 108, the height of the package is not increased as the Schottky diode merely displaces package material above the converter chip. The thickness of discrete Schottky diode can be made as thin as possible during the fabrication process by thinning the backside of the wafer on which the Schottky diodes are formed. In this manner, converter IC 100 is formed including an integrated discrete Schottky diode, thereby reducing the overall component count in applications employing the converter IC.
When Schottky diode 102 is attached to metal pad 106 and mounted on top of converter chip 108 as shown in
Another advantage of using a metal line extension to connect metal pad 106 to bond pad 150 is that the metal pad can now be connected directly to the underlying circuitry of converter chip 108. This electrical connection method is useful in applications when the backside electrode does not need to be brought out of the IC package 110. In this manner, electrical connection to the backside electrode contacted by metal pad 106 can be made to the circuitry of the converter chip without relying on a bond wire connecting the metal pad to a package post to enable a connection back to the underlying converter chip. Of course, in some applications, bond pad 150 can be a “dummy” bond pad not connected to any circuitry of the underlying converter chip and is merely provided to facilitate the wire bonding process of the packaged integrated circuit.
The discrete Schottky diode used in the boost converter integrated circuit in the above description can be fabricated using a variety of diode structure.
Referring to
Aluminum layer 22 forms the anode terminal of Schottky diode 20 while the N++ substrate 34 forms the backside cathode terminal of the Schottky diode.
In one embodiment, the conductive adhesive structure includes a tri-metal layer with conductive epoxy only. The gold layer is not used. In another embodiment, the conductive adhesive structure includes gold with an eutectic die attach. In other embodiments, soft-solder can also be used in place of the epoxy or the eutectic. Other die attach methods, such as ultrasonic, welding, or thermocompression, can also be used to implement the conductive adhesive structure.
In the above descriptions, the metal pad on which the discrete electronic device is mounted is described as a aluminum metal layer formed using one of the metallization layer of the fabrication process used to form the underlying integrated circuit. In other embodiments, the metal pad can be formed using gold or the metal pad can be gold covered. For instance, in one embodiment, the metal pad is formed using a layer of electroless nickel/gold on top of an aluminum layer.
Furthermore, in the above descriptions, the chip-on-chip integrated circuit packaging method is applied to attach one discrete electronic device to an underlying integrated circuit. In other embodiments, the chip-on-chip integrated circuit packing method can also be used to attach two or more discrete electronic devices to an underlying integrated circuit. The two discrete electronic devices can share a common metal pad and therefore have a common backside electrode or the two discrete electronic devices can each be provided with separate, isolated metal pads.
The chip-on-chip integrated circuit packaging method of the present invention provides many advantages. In particular, the method of the present invention provides an optimal solution to the problem of connecting a discrete electronic device to an associated integrated circuit. As described above, it is sometimes not desirable to integrate the electronic device onto the associated integrated circuit as such on-chip integration may require large amount of silicon space and additional fabrication process steps to build the on-chip electronic device. Large amount of silicon space is usually required for devices where the backside terminal needs to be brought up to the topside. On the other hand, it is also undesirable to use a separately packaged discrete electronic device as the discrete electronic device takes up valuable PC board space and increase the component count for the system.
When the chip-on-chip integrated circuit packaging method of the present invention is applied, a discrete electronic device can be “embedded” within the packaging of the associated integrated circuit, thereby avoiding the complexity of integrating the discrete electronic device on-chip while providing an integrated solution to reduce component count and use of PC board space.
The above detailed descriptions are provided to illustrate specific embodiments of the present invention and are not intended to be limiting. Numerous modifications and variations within the scope of the present invention are possible. The present invention is defined by the appended claims.
Claims
1. An integrated circuit package comprising:
- a semiconductor chip having a passivation layer forming the top surface of the semiconductor chip and a metal pad formed on the passivation layer;
- a discrete electronic device having a first terminal formed on a first surface and a second terminal formed on a second surface opposite the first surface of the discrete electronic device, the first surface of the discrete electronic device being attached to the metal pad using a conductive adhesive structure; and
- an encapsulation material encapsulating the semiconductor chip and the discrete electronic device,
- wherein an electrical connection is formed between the metal pad and one of a bond pad of the semiconductor chip or a package post of the integrated circuit package.
2. The integrated circuit package of claim 1, wherein the electrical connection is formed between the metal pad and a first bond pad of the semiconductor chip and the semiconductor chip further includes a metal line connecting the metal pad to the first bond pad.
3. The integrated circuit package of claim 2, wherein the first bond pad connects to circuitry of the semiconductor chip.
4. The integrated circuit package of claim 1, wherein the electrical connection is formed between the metal pad and a first package post of integrated circuit package using a bond wire.
5. The integrated circuit package of claim 1, further comprising a second electrical connection formed using a bond wire from the second terminal on the second surface of the discrete electronic device to one of a bond pad of the semiconductor chip or a package post of the integrated circuit package.
6. The integrated circuit package of claim 1, wherein the metal pad comprises an aluminum pad.
7. The integrated circuit package of claim 1, wherein the conductive adhesive structure comprises a conductive epoxy.
8. The integrated circuit package of claim 1, wherein the conductive adhesive structure comprises a gold layer formed on the first surface of the discrete electronic device and a conductive epoxy layer formed on the gold layer for attaching to the metal pad.
9. The integrated circuit package of claim 8, wherein the gold layer is doped with 0.1% arsenic.
10. The integrated circuit package of claim 1, wherein the discrete electronic device comprises one of a Schottky diode, a VDMOS device, an NPN transistor and a PNP transistor.
11. The integrated circuit package of claim 1, wherein the first surface of the discrete electronic device is roughened using a coarse wheel grinder.
12. A boost converter integrated circuit package comprising:
- a boost converter integrated circuit having a passivation layer forming the top surface of the boost converter integrated circuit and a metal pad formed on the passivation layer;
- a discrete Schottky diode having an anode terminal formed on a topside and a cathode terminal formed on the backside of the Schottky diode, the backside of the discrete Schottky diode being attached to the metal pad using a conductive adhesive structure; and
- an encapsulation material encapsulating the boost converter integrated circuit and the discrete Schottky diode,
- wherein a first electrical connection is formed between the metal pad and a first bond pad of the boost converter integrated circuit, thereby electrically connecting the cathode terminal to the first bond pad and a second electrical connection is formed using a bond wire between the anode terminal on the top side of the Schottky diode and a package post of the integrated circuit package.
Type: Application
Filed: Feb 16, 2007
Publication Date: Jun 21, 2007
Applicant: MICREL, INC. (San Jose, CA)
Inventors: Chuck Vinn (Milpitas, CA), Martin Alter (Los Altos, CA)
Application Number: 11/676,066
International Classification: H01L 23/52 (20060101);