Seal ring structure for radio frequency integrated circuits

Details Seal ring structure for radio frequency integrated circuits Seal ring structure for radio frequency integrated circuits

2001-08-22

2003-03-25

Niebling, John F. (Department: 2812)

Semiconductor device manufacturing: process

Packaging or treatment of packaged semiconductor

C438S637000

Reexamination Certificate

active

06537849

ABSTRACT:

BACKGROUND OF THE INVENTION
(1) Field of the Invention
The invention generally relates to an encapsulation process used in semiconductor manufacturing and, more particularly, to a method of encapsulation that improves isolation of radio frequency (RF) signals in the fabrication of integrated circuits.
(2) Description of Prior Art
As integrated circuit (IC) speeds increase, seal rings have been incorporated into the device encapsulation in order to reduce radio frequency (RF) interference and signal cross coupling. The seal ring is grounded or connected to a signal ground such as a DC supply line to eliminate the effect of interference. The seal ring may be part of the device packaging scheme; in this case a conductive lid is typically connected to the seal ring. Specific to this invention, the seal ring may be incorporated into the IC substrate fabrication and may include a conductive covering over the substrate.
FIG. 1
shows in exploded view a method where the seal ring is incorporated into the device package. A substrate
10
made of ceramic material, for example, has an integrated circuit die
12
attached by a conductive epoxy or eutectic bond. The die
12
is electrically connected to the substrate
10
using bond wires (not shown). A conductive seal ring
14
is attached and grounded by internal connections (not shown). The package is sealed using a lid
16
to prevent penetration by contaminants and moisture.
FIG. 2
shows a top view of an IC die
20
where a seal ring
22
is incorporated. A plurality of bonding pads
24
are shown which may be either signal inputs or outputs, or DC supply and ground. A portion of the circuit containing RF circuits
26
is shown. One problem with this method is that signals from the bonding pads
24
may be capacitively coupled to the seal ring
22
. This may result in unwanted signal interference appearing at one of the signal input or output bonding pads
24
. In addition, interference may be coupled to the RF circuit
26
resulting in signal distortion.
Other approaches employing seal rings exist. U.S. Pat. No. 5,717,245 to Pedder teaches a system using a dielectric multi-layer substrate where RF interference is reduced by grounding certain areas and encapsulating the substrate within a conductive seal ring. U.S. Pat. No. 6,028,497 to Allen et al. teaches a system where RF signals are passed through a network of holes in the base plate of the module. The holes each consist of a conductive pin surrounded by, but electrically isolated from, a conductive cylindrical shroud, thereby forming a coaxial connection. A compartmentalized seal ring attached to the top of the module segregates different circuit areas of the module. U.S. Pat. Nos. 5,864,092 and 6,105,226 to Gore et al. teach methods employing a leadless chip carrier package where a grounded conductor protrudes between input and output signal pads thereby preventing interference. U.S. Pat. No. 5,998,245 to Yu teaches a method where ESD protection is incorporated into a seal ring structure on an IC die. U.S. Pat. No. 6,028,347 to Sauber et al. teaches a method where a portion of the seal ring is formed in trenches in the semiconductor surface. An encapsulating plastic covering over the surface fills the trenches thereby preventing movement of the cover and reducing stresses due to thermal expansion.
SUMMARY OF THE INVENTION
A principal object of the present invention is to provide a method that reduces cross coupling between circuits and pads in an integrated circuit.
Another object of the present invention is to provide a method that prevents cross coupling between circuits caused by the seal ring in an integrated circuit.
These objects are achieved by using a method where a seal ring is formed by stacking interconnected metal layers along the perimeter of the integrated circuit (IC). Discontinuities are formed in the seal ring encapsulating different sections of the IC. There are no overlaps between discontinuities in the seal ring thus isolating signals utilized on different sub-circuits within the IC. To further reduce unwanted signal coupling, the distances between the seal ring and both signal pads and circuits are enlarged. Electrical connection is made between the deep N-well and the seal ring to encapsulate the substrate and minimized signal coupling to the substrate.


REFERENCES:
patent: 5717245 (1998-02-01), Pedder
patent: 5831330 (1998-11-01), Chang
patent: 5864092 (1999-01-01), Gore et al.
patent: 5981384 (1999-11-01), Juengling
patent: 5998245 (1999-12-01), Yu
patent: 6028347 (2000-02-01), Sauber et al.
patent: 6028497 (2000-02-01), Allen et al.
patent: 6054376 (2000-04-01), Balakrishnan
patent: 6105226 (2000-08-01), Gore et al.
patent: 6420208 (2002-07-01), Pozder et al.

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