Active solid-state devices (e.g. – transistors – solid-state diode – Housing or package
Reexamination Certificate
1999-06-17
2001-06-19
Abraham, Fetsum (Department: 2826)
Active solid-state devices (e.g., transistors, solid-state diode
Housing or package
C257S772000, C257S779000, C257S786000, C257S780000, C257S782000, C257S781000, C257S784000, C257S778000
Reexamination Certificate
active
06249044
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention pertains to semiconductor integrated circuits. This invention particularly pertains to flip chip integrated circuits, also known as flip chips. This invention more particularly pertains to light sensitive flip chips and to a flip chip structure that excludes ambient light. The manufacturing process for making integrated circuit chips is performed, not on individual integrated circuit chips, but rather on semiconductor wafers. At the present state of the art many thousands of integrated circuits may be formed on a silicon wafer whose diameter is eight inches. Each circuit is a structure that includes layers of insulator, conductor and semiconductor, each layer being patterned according to a circuit plan. Bonding pads are formed on the surface of the wafer so that each integrated circuit has bonding pads for input signals, output signals, supply voltage, and ground. The wafer is finally cut into a number of integrated circuit chips. Subsequently, each integrated circuit chip is individually processed, either being installed in an integrated circuit package, or being attached to some form of substrate.
In the manufacture of flip chips, some additional process steps are performed on the wafer, prior to the operation of cutting the wafer into individual flip chips. These process steps provide an elevated bump on each bonding pad. Typically, these raised bumps are solder bumps.
A flip chip is attached to a substrate, such as a printed circuit board, by bringing the solder bumps into contact with metal traces on the substrate and then, in one operation, reflowing the solder bumps so as to permanently attach solder bumps to traces.
FIG. 1
shows a cross section of a flip chip
10
attached to a substrate
11
. Each solder bump
12
is attached to a metal trace (not shown) on the substrate
11
. After the flip chip
10
is attached to the
10
substrate
11
, the space between the flip chip and the substrate is commonly filled with a material known as underfill
13
. The underfill material is selected for its mechanical properties so that it redistributes the mechanical and thermnomechanical stresses arising between the flip chip
10
and the substrate
11
. Thus the underfill
13
protects the flip chip
10
from mechanical damage.
In copending application Ser. No. 09/031,167 an invention is disclosed in which protection from mechanical damage is provided in a different way from that just described. A resilient protective layer is applied to the semiconductor wafer before the solder bumps are formed. After the flip chip has been attached to a substrate, the resilient protective layer protects the solder bumps and adjacent regions of the flip chip from mechanical damage arising from mechanical and thermnomechanical stresses arising between the flip chip and the substrate. The resilient layer provides protection against mechanical damage while avoiding the use of underfill. Thus the expense of providing underfill is avoided.
Now, without underfill, the circuit side of the flip chip is exposed to whatever ambient light enters the space between flip chip and substrate. Ambient light includes natural daylight and lamplight. Some flip chips can operate satisfactorily in ambient light. However, some other flip chips are so sensitive to light that their electrical characteristics are altered to an unacceptable degree. These light sensitive flip chips must be isolated from ambient light. Thus a need exists for protection for light sensitive flip chips from ambient light.
SUMMARY OF THE INVENTION
Disclosed herein is a flip chip that comprises a plurality of electrical terminals, each electrical terminal comprising a bonding pad, an under bump pad on the bonding pad, and a solder bump on the under bump pad. Each under bump pad is a portion of an under bump layer. The flip chip further comprises a light shield. The light shield is also a portion of the under bump layer. The light shield portion of the under bump layer is opaque to ambient light and is generally separated from each of the under bump portions of the under bump layer. The under bump layer includes at least one layer of conductive material, and may include multiple layers of conductive materials.
A passivation layer of mechanically resilient insulator material may be present on the wafer before the under bump layer is deposited.
A second layer of mechanically resilient insulator material may be deposited on the light shield.
Alternatively, a layer of titanium or other material that prevents wetting of the light shield by solder may be deposited on the light shield.
The light shield covers at least the light sensitive portions of the flip chip integrated circuit. The area covered by the light shield may a small fraction or a large fraction of flip chip surface.
Thus a flip chip integrated circuit is provided that has self-contained protection from ambient light and that does not require the use of backfill.
REFERENCES:
patent: 4205099 (1980-05-01), Jones et al.
patent: 4816967 (1989-03-01), Landis
patent: 5258334 (1993-11-01), Lantz, II
patent: 5496770 (1996-03-01), Park
patent: 5834844 (1998-11-01), Akagawa et al.
patent: 6022792 (2000-02-01), Ishii et al.
patent: 6034431 (2000-03-01), Goosen et al.
patent: 6049130 (2000-04-01), Housomi et al.
C4 Product Design Manual, Chapter 1—Technology Overview, Issue: A, pp. 1-5 through 1-8 (No date).
Kao Pai-Hsiang
Kelkar Nikhil Vishwanath
Abraham Fetsum
Beyer Weaver & Thomas LLP
National Semiconductor Corp.
LandOfFree
Opaque metallization to cover flip chip die surface for... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Opaque metallization to cover flip chip die surface for..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Opaque metallization to cover flip chip die surface for... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2435982