Stock material or miscellaneous articles – All metal or with adjacent metals – Composite; i.e. – plural – adjacent – spatially distinct metal...
Reexamination Certificate
1998-12-21
2001-01-30
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
All metal or with adjacent metals
Composite; i.e., plural, adjacent, spatially distinct metal...
C428S675000, C428S929000, C219S137510, C219S137510, C257S738000
Reexamination Certificate
active
06180265
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to surface-mount integrated circuit devices. More particularly, this invention relates to surface-mount integrated circuit devices configured for electrical connection by wire bonding, and to a method by which wire bond pads on such a device are modified to yield flip chip solder bump pads that enable the device to be flip-chip mounted to a conductor pattern.
BACKGROUND OF THE INVENTION
A flip chip is generally a monolithic semiconductor device, such as an integrated circuit (IC), having bead-like terminals formed on one of its surfaces. The terminals, usually in the form of solder bumps, serve to both secure the flip chip to a circuit board and electrically interconnect the chip circuitry to a conductor pattern formed on the circuit board. Flip chip technology is compatible with a variety of circuit board types, including ceramic substrates, printed wiring boards, flexible circuits, and silicon substrates. The solder bumps are typically located at the perimeter of the flip chip on electrically conductive bond pads that are electrically interconnected with the circuitry on the flip chip. Due to the numerous functions typically performed by the microcircuitry of a flip chip, a relatively large number of solder bumps are often required. The size of a flip chip is typically on the order of about thirteen millimeters per side, resulting in the solder bumps being crowded along the perimeter of the flip chip. As a result, flip chip conductor patterns are typically composed of numerous individual conductors that are often spaced apart about 0.1 millimeter or less.
Flip chips are widely used in the electronics industry as a result of their compact size and their characteristic of being directly attached to substrates without additional packaging. Another process for directly attaching an IC device to a substrate is by the wire bonding process. Such an IC device has a number of bond pads that are wire bonded to bond pads of a complementary conductor pattern on the substrate to which the device is being attached. The bond pads on the IC device are typically aluminum or an aluminum-base alloy for various known processing and performance-related reasons. The wire is often gold, which will bond well with the aluminum bond pad if the bonding operation is properly performed.
Though wire-bonded ICs are widely used, flip chips are generally smaller, less expensive to mount, and more versatile, being suitable for a wider variety of electronic products than are chip-and-wire ICs. Consequently, there has evolved a demand for flip chip bumping and attachment of surface-mount devices that were originally designed for attachment by wire bonding. Several alternatives have been contemplated for this conversion process. One example is illustrated in
FIGS. 1A through 1C
, which show an IC device
10
on which a wire bond pad
12
has been formed. The bond pad
12
is conventionally formed of aluminum or an aluminum-base alloy, and is therefore susceptible to corrosion if left exposed. Consequently, a passivation layer
16
overlies the surface of the device
10
, with a square-shaped opening
14
being formed in the passivation layer
16
to expose an interior region of the bond pad
12
. However, the exposed region of the bond pad
12
is too large for forming a solder bump for flip-chip mounting the device
10
. In particular, any attempt to form a solder bump on the exposed region of the bond pad
12
would yield a solder bump having inadequate height and a tendency to short with adjacent solder bumps.
Therefore, the process of
FIGS. 1A-1C
further entails depositing a second passivation layer
18
on the bond pad
12
and the original passivation layer
16
, and then developing a circular-shaped opening
20
in the second passivation layer
18
, as shown in FIG.
1
B. This step generally can be performed by spinning an organic dielectric material on the substrate
10
, photolithographically developing the opening
20
using known methods, and then curing the dielectric material. The opening
20
shown in
FIG. 1B
is sized and shaped to enable the deposition of a controlled amount of solderable material
22
on that portion of the bond pad
12
re-exposed by the opening
20
, the result of which is illustrated in FIG.
1
C. The solderable material
22
forms a bond pad that enables solder to be deposited and reflowed to form a suitable solder bump (not shown).
Though the process represented in
FIG. 1A through 1C
yields a suitable bond pad for a flip chip solder bump, the requirement for an additional passivation layer
18
and a masking operation to form the opening
20
represent a significant impact on processing costs and scheduling.
In view of the above, it would be desirable if a process were available that enabled wire bond pads to be converted to flip chip solder bump pads, but that avoided the cost and processing disadvantages of additional masking operations.
SUMMARY OF THE INVENTION
It is an object of this invention to provide a method for converting an aluminum wire bond pad to a flip chip solder bump pad, so as to enable an IC device originally configured for wire-bonding attachment to be mounted using a flip chip attachment technique.
It is a further object of this invention that such a method does not entail an additional masking operation.
It is another object of this invention that such a method yields a bond pad structure that protects the original aluminum wire bond pad.
In accordance with a preferred embodiment of this invention, these and other objects and advantages are accomplished as follows.
According to the present invention, there is provided a method for forming a solder bump pad, and more particularly converting a wire bond pad of a surface-mount IC device to a flip chip solder bump pad, such that the IC device can be flip-chip mounted to a substrate. As such, the process of this invention generally entails an aluminum wire bond pad on a substrate, with at least a portion of the wire bond pad being exposed through a dielectric layer on the substrate. A nickel layer is then deposited on the portion of the wire bond pad exposed through the dielectric layer. The nickel layer is selectively deposited on the exposed portion of the wire bond pad without use of a masking operation, such as by an electroless deposition technique. The nickel layer completely overlies the aluminum wire bond pad, and therefore protects the bond pad from oxidation due to exposure. Thereafter, a solderable material is deposited on the nickel layer, such that the solderable material forms the solder bump pad. The solder bump pad is formed to cover only a limited portion of the nickel layer, and its shape is tailored to achieve the required geometric characteristics for a solder bump subsequently formed thereon.
As described above, the process of this invention yields a flip chip solder bump pad from a wire bond pad without requiring an additional passivation layer or masking operation to properly size and shape the solder bump pad. Accordingly, this invention avoids the significant impact on processing costs and scheduling that these additional steps would incur, while achieving the accuracy and integrity required for flip chip bonding techniques.
Other objects and advantages of this invention will be better appreciated from the following detailed description.
REFERENCES:
patent: 4950623 (1990-08-01), Dishon
patent: 5137845 (1992-08-01), Lochon et al.
patent: 5268072 (1993-12-01), Agarwala et al.
patent: 5310701 (1994-05-01), Kaussen et al.
patent: 5376584 (1994-12-01), Agarwala
patent: 5542174 (1996-08-01), Chiu
patent: 5856705 (2000-05-01), Ting
patent: 5923955 (1999-07-01), Wong
patent: 5989993 (1999-11-01), Zakel et al.
patent: 6066551 (2000-05-01), Satou et al.
patent: 97/18584 (1997-05-01), None
Delco Electronics Corporation
Funke Jimmy L.
Jones Deborah
Savage Jason
LandOfFree
Flip chip solder bump pad does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Flip chip solder bump pad, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Flip chip solder bump pad will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2544985