Patent Application
20110057741
The present invention relates to a device and method for interfacing between an integrated circuit and a waveguide and, more particularly, but not exclusively to providing an interface that is efficient at radio and mm-wave frequencies.
A problem arises as to how to create a low loss interface between a millimeter-wave RFIC and a wave-guide.
Current IC production techniques allow a number of types of mechanical structures that can be used to interface IC signals. In order to drive a signal in and out of a wave-guide the mechanical structure needs to comply with specific electromagnetic requirements. In order to drive a millimeter-wave signal between the IC signal interface and the wave-guide's own interface, another mechanical structure is required, the structure having its own electromagnetic requirements in order to drive the electromagnetic signal with minimal loss of signal power.
The difficulty existing today is that the known interfacing techniques still dissipate the signal's power and are relatively complicated and costly to implement. The systems in use today for connecting the integrated circuit to the PCB are wire bonding and tape automatic bonding. Wire bonding uses gold, aluminium or copper wires to connect an IC to a substrate. The bonding is flexible and tolerant of thermal expansion and is also relatively cheap. Parasitic effects such as skin effect resistance, radiation loss, mutual coupling between bonding wires, and wire inductances are however present, and difficult to control or model.
Tape automated bonding (TAB) uses patterned metal leads to connect between IC and substrate. An IC is first attached to an inner rim of the patterned leads using gold, aluminium or solder bumps. The attached IC is then mounted on the substrate.
TAB technology can be highly automated, is very precise and allows for gang bonding—meaning that all leads are bonded simultaneously. However the metal leads are of non-uniform width and are closely spaced, leading to electrical characteristics which are difficult to predict or model. TAB technology is also relatively expensive.
U.S. Pat. No. 7,109,122 is an example of the kind of interface according to the current art which still dissipates signal power.
US Patent Application Publication No. 2008/0266196 deals with details of a conventional waveguide feed mechanism.
According to one aspect of the present invention there is provided a low-loss interface between a mm-wave integrated circuit and a waveguide. The interface is constructed by:
providing a surface having a contact location for the integrated circuit and a waveguide location for fixing a waveguide thereon;
providing a transmission line extending along the surface from the contact location substantially to the waveguide location and extending into the waveguide location as a waveguide feed;
providing a plurality of connection bumps on a surface of the mm-wave integrated circuit; and
connecting the mm-wave integrated circuit to the surface at the contact location through the connection bumps, such that a first of the connection bumps connects a signal output of the mm-wave integrated circuit to the transmission line, thereby providing the low loss interface.
In an embodiment, the plurality of connection bumps are connection bumps of a flip chip interconnection system.
In an embodiment, the mm-wave integrated circuit comprises an interface for a transmission line on a lower surface thereof, and wherein the signal output is a signal output of the transmission line.
In an embodiment, a waveguide location comprises a cavity for receiving the waveguide.
An embodiment may involve constructing a waveguide backshort around the cavity to reflect energy into the waveguide.
An embodiment may comprise constructing the waveguide backshort from a metal casing over the surface.
In an embodiment, the transmission line is mounted on a millimeter wave substrate, and wherein a ground connection to the mm-wave integrated circuit is made through the millimeter wave substrate to another of the connection bumps.
In an embodiment, the transmission line is mounted on a millimeter wave substrate and comprising implementing the cavity as part of the millimeter wave substrate.
The cavity may be plated.
According to an aspect of the present invention there is provided a low-loss interface between a mm-wave integrated circuit and a waveguide, comprising:
a surface having a contact location for the integrated circuit and a waveguide location for fixing a waveguide thereon;
a transmission line extending along the surface from the contact location substantially to the waveguide location and extending into the waveguide location as a waveguide feed;
a plurality of connection bumps on a surface of the mm-wave integrated circuit providing a connection between the mm-wave integrated circuit and the surface at the contact location, such that a first one of the connection bumps connects a signal output of the mm-wave integrated circuit to the transmission line, thereby providing the low loss interface.
According to a further aspect of the present invention there is provided a method of manufacturing a connection for a waveguide to a PCB, comprising:
printing on a low loss substrate a feed, the feed being an extension of a transmission line;
cutting a cavity under said feed;
providing a metal plating around said cavity;
laminating the low loss substrate onto the PCB after said metal plating has been provided, such that said metal plating extends between said laminated layers about said cavity to a first extent about said cavity,
placing a metal cap over the substrate, the metal cap being electrically connected to the metal plating, and
placing the waveguide in contact with the cavity such that the cavity forms a continuation with the waveguide.
The method may comprise connecting said metal cap to said metal plating using vias, the vias being within said first extent.
In an embodiment, the waveguide is for carrying a signal of a predetermined wavelength and an alternative to the use of vias is to provide a shoulder is added to said metal cap, said shoulder being a quarter of the predetermined wavelength.
The waveguide may be for carrying a signal of a predetermined wavelength and the PCB may then be a quarter of the predetermined wavelength.
Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The materials, methods, and examples provided herein are illustrative only and not intended to be limiting.
The word “exemplary” is used herein to mean “serving as an example, instance or illustration”. Any embodiment described as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments and/or to exclude the incorporation of features from other embodiments.
The word “optionally” is used herein to mean “is provided in some embodiments and not provided in other embodiments”. Any particular embodiment of the invention may include a plurality of “optional” features unless such features conflict.
Implementation of the method and/or system of embodiments of the invention can involve performing or completing selected tasks manually, automatically, or a combination thereof. This refers in particular to tasks involving the RFIC itself.
The invention is herein described, by way of example only, with reference to the accompanying drawings. With specific reference now to the drawings in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the preferred embodiments of the present invention only, and are presented in order to provide what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice.
In the drawings:
The present embodiments comprise the use of flip chip style interconnection bumps from an underside ground-signal-ground interface of an RFIC to a microstrip transmission line to link via a waveguide feed to a waveguide, thereby providing an efficient interface between the RFIC and the waveguide. The connection bump is located over the ground-signal-ground signal output of the RFIC and over the microstrip transmission line and forms a connection therebetween. The dielectric overlap between the RFIC and the PCB may be minimized.
The principles and operation of an apparatus and method according to the present invention may be better understood with reference to the drawings and accompanying description.
Before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments or of being practiced or carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein is for the purpose of description and should not be regarded as limiting.
Reference is now made to
A transmission line 24 extends along the surface from contact location 20 to waveguide location 22. The transmission line extends into the waveguide location 22 as a waveguide feed 26. The waveguide feed, as an extension of the microstrip transmission line, may be, or may be based on, a conventional monopole feed.
Connection bumps 28 and 30 are part of a flip chip connection system and are located on the contact side of the RFIC 10. The connection bumps make a connection between the RFIC 10 and the surface at contact location 20. The connection is direct and there are no intervening wires. The bump height may be minimized, in order to avoid detuning effects and to have low parasitic inductance. One of the connection bumps 28 connects a signal output 32 of the mm-wave integrated circuit 10 to transmission line 24, thus providing the low loss interface.
That is to say, the RFIC interface is based on flip chip style interconnection bumps. The microwave signal transmission line comprises three bumps organized in a Ground-Signal-Ground structure. The Ground-Signal-Ground structure is very natural for implementation of analogue circuitry inside the RFIC and yields a transmission line with characteristic impedance of between 100 and 170 Ohm and typically at about 150 Ohm at a physical length in a typical range of 30-80 μm and in particular about 40 μm.
The same Ground-Signal-Ground structure implemented using wire-bonds may create a transmission line with the same characteristic impedance but with a physical length in the range of 200-400 μm and most typically 300 μm. The reduced length of the transmission line using flip-chip may enable a much simpler matching structure using the present embodiments.
The RFIC interface can also be of a balanced nature, meaning be based on two complementary signal lines.
As mentioned above, the connection bumps are part of a flip chip interconnection system, and the chip 10 may be packaged or unpackaged. The flip chip connections allow for wafer level packaging so that the resulting structure does not have to be sealed.
Flip chip connections provide short and stable connections. Nevertheless, the use of flip chip connections is not straightforward, and issues arise that include parasitic reactance at the bump interconnection, a detuning effect on the RFIC circuits and excitation of parasitic substrate modes.
The number of connection bumps is preferably minimized in order to reduce mutual coupling effects.
The bump diameter and dielectric overlap indicated by arrow 51 in
The waveguide location 22 comprises a cavity 34 which extends into the PCB 14 and the ground layer 16, and serves for receiving the waveguide 12. The walls of the PCB around the cavity may be plated with plating 36, which is a continuation of the ground layer 16.
An alternative technique, based on having a PCB thickness of quarter of a wave-length, allows the cavity to be either plated or unplated.
The waveguide location may further comprise a waveguide backshort 38 around the cavity to reflect energy into said waveguide. The backshort 38 may be constructed from a metal casing 40 extending from the PCB surface. The metal casing 40 may be connected to the ground layer 16 via connection 41 through the millimeter wave substrate 18 and preferably back to the ground layer 16.
The transmission line is mounted, that is typically printed, on millimeter wave substrate 18. Reference is now made to
RFIC 10 may have numerous connection bumps, of which only 2 are illustrated. These are respectively located over the ground and signal outputs of the ground-signal-ground interface that is provided on the underside of the RFIC 10. The underside of the RFIC, showing the ground-signal-ground interface, is as illustrated in
As explained, the bump 28 that is located over the signal output is electrically connected to the microstrip transmission line 24.
A ground connection is made from the ground 42 of the chip ground-signal-ground interface (shown in
The cavity 34 may be a part of or extend into the millimeter wave substrate, with the ground layer and millimeter wave substrate being cut away from within the cavity.
Arrow 51 illustrates the dielectric overlap between the RFIC 10 and the microwave transmission line 24. The dielectric overlap is preferably minimized in order to reduce reflection.
Other types of possible waveguide-feeds include a tapered-slotline-probe. The probe may be based on a balanced drive and a radiating-slot, and thus eliminate the need for the back-short 38.
A method of construction of the embodiment of
Connection bumps 28 and 30 are part of a flip chip connection system and are located on the contact side of the RFIC 10. The connection bumps make a connection between the RFIC 10 and the surface at contact location 20. The connection is direct and there are no intervening wires. The bump height may be minimized, in order to avoid detuning effects and to have low parasitic inductance. One of the connection bumps 28 connects a signal output 32 of the mm-wave integrated circuit 10 to transmission line 24, thus providing the low loss interface. Ground plane 50 surrounds the transmission line 24 so that in this embodiment, no tunneling is required.
Vias 41 connect the ground plane 50 to the metallic coating around the waveguide, as shown in greater detail with respect to
One purpose of the structure of the present embodiment is to provide cost reduction in the construction of an efficient interface.
To this end, the wave-guide interface serves to facilitate a transformation from the CPWG structure to the waveguide, which waveguide has metallic walls. In order to have a low-cost implementation of such a transformation medium, the implementation thereof is based on the same substrate holding the RFIC and the CPWG. The transformation medium is composed of the following:
A transmission line 24 is thus provided between the RFIC interface and the wave-guide interface. In order to have a low-cost transmission line implementation the structure of the present embodiment may be based on a single layer of low-loss, soft or organic laminates such as Rogers 4350B, or Taconic reinforced by low-cost FR4 material. Such material of course does not participate in the electromagnetic signal path. The selected wave-guide structure is a Grounded-Coplanar-Waveguide (CPWG). The Ground-Signal-Ground native structure of the top layer of the CPWG makes it an ideal candidate for interfacing the RFIC microwave ports. The grounded part of the CPWG enables the separation between the electromagnetic signal path and the FR-4 reinforcement section. Another advantage of the CPWG is its low radiation losses compared to regular micro-strip structures.
Another type of transmission line that can be used is a slot-line. The slot line is advantageous in that it has lower propagation loss.
Reference is now made to
In accordance with the embodiments of
printing a feed onto a low loss substrate a feed, the feed being an extension of a transmission line;
cutting a cavity underneath the feed into the PCB structure;
providing a metal plating around the cavity walls;
laminating the low loss substrate onto the PCB after the metal plating has been provided, thus ensuring that the metal plating extends between the laminated layers around the cavity. This is followed by placing a metal cap over the substrate. The metal cap may then be electrically connected to the metal plating. This is followed by placing the waveguide in contact with the cavity such that the cavity forms a continuation with the waveguide.
The metal cap may then be connected to the metal plating using vias which are located within the radius of the laminated layers. The vias ensure electrical conduction between the metal cap and the metal plating to provide a continuous ground layer.
The combination of flip-chip connections, microstrip or CPWG transmission line and waveguide feed may provide a significant reduction in power loss as compared with conventional designs. The combination is also easier to simulate than conventional designs. In particular the use of connection bumps helps to minimize parasitic reactance and radiation and reflection losses at the interface.
It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable subcombination.
Although the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims. All publications, patents, and patent applications mentioned in this specification are herein incorporated in their entirety by reference into the specification, to the same extent as if each individual publication, patent or patent application was specifically and individually indicated to be incorporated herein by reference. In addition, citation or identification of any reference in this application shall not be construed as an admission that such reference is available as prior art to the present invention.
