Chip scale surface mount packages for semiconductor device...

Semiconductor device manufacturing: process – Packaging or treatment of packaged semiconductor – Making plural separate devices

Reexamination Certificate

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C438S114000, C438S460000, C438S462000, C438S464000, C438S465000, C438S928000

Reexamination Certificate

active

06316287

ABSTRACT:

BACKGROUND OF THE INVENTION
After the processing of a semiconductor wafer has been completed, the resulting integrated circuit (IC) chips or dice must be separated and packaged in such a way that they can be connected to external circuitry. There are many known packaging techniques. Most involve mounting the die on a leadframe, connecting the die pads to the leadframe by wire-bonding or otherwise, and then encapsulating the die and wire bonds in a plastic capsule, with the leadframe left protruding from the capsule. The encapsulation is often done by injection-molding. The leadframe is then trimmed to remove the tie bars that hold it together, and the leads are bent in such a way that the package can be mounted on a flat surface, typically a printed circuit board (PCB).
This is generally an expensive, time-consuming process, and the resulting semiconductor package is considerably larger than the die itself, using up an undue amount of scarce “real estate” on the PCB. In addition, wire bonds are fragile and introduce a considerable resistance between the die pads and the leads of the package.
The problems are particularly difficult when the device to be packaged is a “vertical” device, having terminals on opposite faces of the die. For example, a power MOSFET typically has its source and gate terminals on the front side of the die and its drain terminal on the back side of the die. Similarly, a vertical diode has its anode terminal on one face of the die and its cathode terminal on the opposite face of the die. Bipolar transistors, junction field effect transistors (JFETs), and various types of integrated circuits (ICs) can also be fabricated in a “vertical” configuration.
Accordingly, there is a need for a process which is simpler and less expensive than existing processes and which produces a package that is essentially the same size as the die. There is a particular need for such a process and package that can be used with semiconductor dice having terminals on both their front and back sides.
SUMMARY OF THE INVENTION
The process of fabricating a semiconductor device package in accordance with this invention begins with a semiconductor wafer having a front side and a back side and comprising a plurality of dice separated by scribe lines. Each die comprises a semiconductor device. A surface of the front side of each die comprises a passivation layer and at least one connection pad in electrical contact with a terminal of the semiconductor device. The back side of each die may also be in electrical contact with a terminal of the semiconductor device.
The process comprises the following steps: forming a first metal layer in electrical contact with the connection pad, a portion of the first metal layer extending laterally beyond an edge of the die; attaching a cap to the front side of the wafer; cutting through the semiconductor wafer from the back side of the wafer in the scribe line area to form a first cut, the first cut having a first kerf W
1
and exposing a part of the first metal layer; forming a nonconductive layer on the back side of the die; forming a second metal layer, the second metal layer having a first section extending over the nonconductive layer and being in electrical contact with the first metal layer; and cutting through the cap in the scribe line area to form a second cut having a second kerf W
2
that is less than the first kerf W
1
, the second cut leaving in place an area of contact between the first and second metal layers.
In many embodiments, the process also includes forming a second section of the second metal layer in electrical contact with the backside of the semiconductor wafer, the first and second sections of the second metal layer being electrically insulated from each other. The process may also include grinding, lapping or etching the back side of the semiconductor wafer to reduce the thickness of the wafer after attaching the cap to the front side of the wafer.
In one aspect, the invention includes a process for making an electrical connection between a first location on a first side of a semiconductor die and a second location on a second side of the semiconductor die. The process commences while the die is a part of a semiconductor wafer. The process comprises forming a first metal layer extending laterally from the first location on the first side of the die to an area of the wafer beyond an edge of the die; attaching a cap to the first side of the wafer; cutting through the semiconductor wafer from the second side of the wafer to expose a part of the first metal layer; forming a second metal layer extending laterally from the second location on the second side of the die and along an edge of the die to a region of contact with the first metal layer beyond the edge of the die; and cutting through the cap while leaving intact the region of contact between the first and second metal layers.
This invention also includes package for a semiconductor device. The package comprises a cap having a width X
1
; a semiconductor die containing a semiconductor device, the die being attached to the cap with a front side of the die facing the cap and a back side of the die facing away from the cap, the die having a width X
2
that is less than X
1
; a connection pad in electrical contact with the semiconductor device, the contact being located between the die and the cap and having a width no greater than X
2
; a first metal layer in electrical contact with the connection pad, a first portion of the first metal layer being located between the connection pad and the cap and a second portion of the first metal layer extending laterally beyond an edge of the connection pad; a second metal layer having first and second sections, the first section of the second metal layer being in contact with the second portion of the first metal layer, the second section being in electrical contact with the backside of the wafer, the first and second sections of the second metal layer being electrically insulated from each other.
In yet another aspect, this invention includes a package for a semiconductor device comprising a semiconductor die containing a semiconductor device, a first side of the die comprising a connection pad; a cap attached to the first side of the die, an edge of the cap extending laterally beyond an edge of the die; a first metal layer in electrical contact with the connection pad, the first metal layer extending laterally and terminating in a first flange beyond an edge of the die; and a second metal layer extending from a second side of the die and along an edge of the die and terminating in a second flange beyond the edge of the die, the second flange being in contact with the first flange.
Semiconductor packages according to this invention do not require an epoxy capsule or bond wires; the substrate attached to the die serves to protect the die and acts as a heat sink for the die; the packages are very small (e.g., 50% the size of molded packages) and thin; they provide a very low on-resistance for the semiconductor device, particularly if the wafer is ground thinner; they are economical to produce, since they require no molds or lead frames; and they can be used for a wide variety of semiconductor devices such as diodes, MOSFETs, JFETs, bipolar transistors and various types of integrated circuit chips.


REFERENCES:
patent: 5270261 (1993-12-01), Bertin et al.
patent: 5753529 (1998-05-01), Chang et al.
patent: 5757081 (1998-05-01), Chang et al.
patent: 5767578 (1998-06-01), Chang et al.
patent: 5888884 (1999-03-01), Wojnarowski
patent: 5998238 (1999-12-01), Kosaki
patent: 6153448 (2000-11-01), Takahashi et al.
patent: 6159767 (2000-12-01), Eichelberger
patent: WO 98/19337 (1998-05-01), None
Lawrence Kren, “The Race For Less Space”, Machine Design, Jul. 8, 1999, pp. 86-89.
Patrick Mannion, “MOSFETs Break Out Of The Shackles Of Wirebonding”, Electronic Design, Mar. 22, 1999, vol. 47, No. 6, pp. 1-5.

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