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"Interconnection Device for Electronic Circuits, Notably Microwave Electronic Circuits" in Patent Application Approval Process

July 16, 2014



By a News Reporter-Staff News Editor at Defense & Aerospace Week -- A patent application by the inventors DENIS, Stephane (LA BOUEXIERE, FR); LEDUC, Dominique (RENNES, FR); FORTEL, Julien (RENNES, FR); FOUIN, Patrick (VERN SUR SEICHE, FR); BRIANTAIS, Didier (ETRELLES, FR), filed on December 18, 2013, was made available online on July 3, 2014, according to news reporting originating from Washington, D.C., by VerticalNews correspondents.

This patent application is assigned to Thales.

The following quote was obtained by the news editors from the background information supplied by the inventors: "The present invention relates to applications for which electrical links are required, between different electronic circuits. After, the concept of electronic circuit should be understood in its widest sense, that is to say that an electronic circuit can take the form of an electronic module, for example a chip, a micro-electro-mechanical system, usually referred to by the acronym 'MEMS', a packaged integrated circuit, a module of single or stacked printed circuit boards, a three-dimensional module, etc. These links can electrically interlink physically uniform electronic circuits, for example chips, or even physically dissimilar electronic circuits, when the aim is, for example, to electrically link a chip with an interconnection support with a substrate, a printed circuit board, a package, etc. The signals concerned may be of fast digital or even microwave analogue nature.

"More particularly, the present invention relates to applications in which the abovementioned electrical links are intended for the transmission of electrical signals occupying a wide frequency band, and/or which are situated in high frequencies in respect of the dimensions of the links to be produced, and/or which exhibit high power levels. The signals concerned may be of analogue or digital nature. It is, for example, considered that high frequencies in respect to the dimensions of the links to be produced observe the inequality ll>3.10.sup.9/1000.f, ll representing the link length in metres, and f representing the frequency of the transmitted signal, in Hertz.

"When this inequality is not satisfied, the link produced is all the more difficult to compensate when the characteristic impedance of the interfaces is low, when the required matching level is high, and when the frequency band of interest is wide. Implanting a matching network is not always possible, either because the space available is insufficient, or because the elements to be interconnected are fixed and cannot be modified.

"In order to limit the interfering influence of the link elements, produced for example in the form of wires or tapes, the electronic circuits which have to be electrically linked are placed as close as possible to one another. The fastenings of the link elements are, for example, produced by thermocompressed or thermosonic bonding techniques. Consequently, the dimensions and the tolerances which are associated therewith and which are associated with the positioning of the elements, are reduced, to the detriment of the production costs and manufacturing output.

"This drawback is all the more critical when the assemblies concerned are complex and long chains of dimensions are involved. For example, in a relatively simple case where chips or power modules are mounted on heat dissipaters, through cavities produced in a substrate, a chain of dimensions can be defined as the sum of the distance from the pad on the substrate relative to the edge of the substrate, of the distance from the edge of the substrate to the edge of the chip or of the module, and of the distance from the edge of the chip or of the module to the land on the chip or the module. A fine tolerance associated with such a chain of dimensions is in practice feasible, but at the price of necessarily costly manufacturing and inspection methods, and at the risk of low output.

"Another problem that arises in this context is linked to the fact that it is sometimes necessary to link components in assemblies in which the latter have fixing points situated at different heights. In such cases, not only does the height difference between the components or circuits increase the link length, but also it proves difficult to produce a ground return.

"There are solutions known from the prior art, that are implemented to limit the influence of interference phenomena or the mismatching of the connections.

"A first known technique consists in using connection leads, which can take various forms. These connection leads can, for example, be through-spikes, lyres, or even flat leads mounted on the surface of printed circuits. One drawback with this technique is that it is not effective for the transmission of high frequency signals, and for the dissipation of high power levels.

"A second known technique consists in using micro-wiring comprising a plurality of conductive wires in parallel, usually two wires. Such a technique is, however, often limited by the surface area available from the lands, the surface area of which is limited by the frequency of the signals to be transmitted. It is also limited by the phenomenon of mutual inductance between the conductive wires.

"A third known technique consists in using micro-wiring comprising micro-ribbons. This technique, however, also presents the drawback of being limited by the surface area available on the lands, the surface area of which is limited by the frequency of the signals to be transmitted. Another drawback with this technique is that it is significantly more costly to implement industrially, by comparison with the abovementioned second wired technique.

"A fourth known technique consists in using conductive microballs, soldered between metallized lands of modules mounted flipped relative to one another. This technique is known by the technical name 'flip-chip'. For example, an electronic chip or a module equipped with a matrix of conductive balls--often referred to by the acronym BGA, which stands for 'Ball Grid Array'--mounted flipped on a substrate. This technique is advantageous for very high frequency links, and/or links with a very wide frequency band. However, this technique is costly to implement industrially, and requires additional steps in the process of manufacturing the devices that implement them. Furthermore, this technique presents the drawback of not being effective in terms of heat dissipation, when it is applied to monolithic electronic circuits, of chip type. It may prove effective when it is applied to modules incorporating a heat dissipater, but in such cases the technique proves overall very costly to implement industrially. This technique also presents the drawback of requiring chips or modules that are designed specifically for this type of assembly. Lastly, it presents a drawback associated with the difficulty, even impossibility, to carry out visual inspections on the links after assembly.

"A fifth known technique consists in using micro-lands, assembled directly by soldering or by bonding on electronic circuits mounted flipped relative to one another. This technique is similar to the fourth known technique using microballs, described above. For example, an electronic chip or a module equipped with a matrix of metallized micro-lands--often referred to by the acronym LGA, standing for 'Land Grid Array'--mounted flipped on a substrate. This technique also makes it possible to produce very high frequency and/or very wide band links. On the other hand, this technique is not effective for ensuring the matching of the differences in expansion coefficients between the different electronic circuits. In a way similar to the fourth technique described above, this technique presents the drawback of not being effective in terms of heat dissipation, when it is applied to monolithic electronic circuits, of chip type. It may also prove effective when it is applied to modules incorporating a heat dissipater, but at the price of very costly implementation. This technique also presents the drawback of requiring chips or modules that are designed specifically for this type of assembly. It also presents a drawback associated with the difficulty, even impossibility, of carrying out visual inspections of the links after assembly, even when some links are produced with lands which rise up on the sides, for example for modules provided with castellations, according to LGA-specific techniques.

"A sixth known technique consists in using micro-bump contacts intended for the production of links by thermocompression or by bonding. This technique makes it possible to produce very high frequency links and/or links with a very wide frequency band. However, this technique does not make it possible to ensure an effective heat dissipation. It also presents a drawback associated with the difficulty, even the impossibility, of carrying out visual inspections on the links after assembly.

"A seventh known technique consists of tape-automated bonding, usually referred to by the acronym 'TAB'. This technique is based on an electronic circuit produced on a thin and flexible substrate, the tracks of which extend beyond and are directly micro-wired to the interconnection bump contacts of the elements to be linked, for example by thermocompression or by collective soldering. This technique allows for a collective link mode, that is to say that all the connection operations for one and the same printed circuit can be carried out simultaneously. The TAB technique makes it possible, for example, to produce links with coplanar transmission lines, of ground/signal/ground type. Such lines present the drawback of being sensitive to dissymetries, of requiring a minimum of six contact points per link, of requiring ground planes of large surface area, as well as great delicacy in the production of the central line, in terms of track width and of separation from the ground lines, in order to obtain typical characteristic impedances of the order of 50.OMEGA.."

In addition to the background information obtained for this patent application, VerticalNews journalists also obtained the inventors' summary information for this patent application: "One aim of the present invention is to mitigate the drawbacks specific to the abovementioned known devices, by proposing an interconnection device for microwave electronic circuits, that can replace the known interconnection techniques, more often than not wired, or also the coplanar transmission lines of ground/signal/ground type used for the production of links according to techniques of TAB type. An interconnection device according to the invention allows for the transmission of electrical signals occupying a wide frequency band and/or situated in high frequencies with respect to the dimensions to be produced and/or exhibiting high power levels, with a high matching level.

"The present invention proposes electrically linking the electronic circuits with an element forming a transmission line of appropriate length and characteristic impedance. This approach is different from the known wired link approaches which are more localized in nature, whereas a transmission line is of distributed nature. This transmission line exhibits a characteristic impedance and in some very favourable cases, a propagation mode, that are very close to those which are exhibited at the interfaces of the electronic circuits to be linked.

"The present invention makes it possible to electrically link microwave components by providing a very wide bandwidth and/or an interconnection distance and/or a matching level superior to what can be produced via the techniques known from the prior art. For a given matching level and bandwidth, the maximum distances that can be allowed between elements to be connected with an interconnection device according to one of the embodiments of the present invention are greater than with the solutions known from the prior art. These greater distances make it possible to increase all the dimensions and most of the tolerances on the dimensions associated with the interconnection, such as, for example, the cutting accuracies and distances for the interconnected elements or the machining accuracies and dimensions for the supports.

"Because the interconnection device according to the various embodiments of the invention forms a transmission line, the performance levels --for example the insertion and matching losses--of the electrical link depend little on its length, up to the cut-off frequency of the link, which more often than not results from a spurious resonance which also involves elements that are 'peripheral' to the interconnection, such as, for example, vias and ground pads at the leads of integrated circuits of 'MMIC' (Monolithic Microwave Integrated Circuit) type or of modules. Such is not the case with known links using wires or ribbons.

"One advantage of the invention is that it makes it possible to produce electrical links of transmission line type, with dimensions that make it possible to relax the elements of a chain of dimensions, and move the lands further apart.

"Another advantage of the invention is that it makes it possible to produce interconnection devices with dimensions that are smaller than links produced with coplanar lines of ground/signal/ground type, that are less complex to assemble, and that have a lower immunity to interference phenomena.

"Another advantage of the invention is that the type of electrical link that it proposes better supports high electrical power levels compared to wired links.

"Yet another advantage of the invention is that the type of electrical link that it proposes better contains the electromagnetic fields, by comparison with wired links or with ribbon links of comparable size. This makes it possible to minimize the spurious couplings between electronic circuits arranged in proximity to one another.

"Yet another advantage of the invention is that it makes it possible to tolerate variations of dimensions associated with the possible temperature variations and with the different expansion coefficients of the materials implemented, that can typically induce relative movements of the order of a micron.

"To this end, the subject of the invention is an interconnection device for elements to be interconnected such a electronic modules or circuits, comprising at least one transmission line coupled to a ground line, the two lines being produced on a face of a dielectric substrate, the interconnection being made substantially at the ends of the transmission line and of the ground line, the device being characterized in that it is flexible over at least a part of its length situated roughly between the elements to be interconnected.

"In one embodiment of the invention, the device can also comprise at least one metallization surface forming, on the other face of the dielectric substrate at least one coupling element for reinforcing the electrical coupling between the two lines.

"In one embodiment of the invention, said part of the length of the interconnection device can be made flexible by at least one narrowing of the width of the transmission and ground lines.

"In one embodiment of the invention, said part of the length of the interconnection device can be made flexible by at least one folding of the transmission and ground lines.

"In one embodiment of the invention, the folding of the transmission and ground lines can take the form of a zigzag, in the plane containing the transmission and ground lines.

"In one embodiment of the invention, the folding of the transmission and ground lines can take the form of a bend, in the plane containing the transmission and ground lines.

"In one embodiment of the invention, the folding of the transmission and ground lines can have the form of a bend, on an axis orthogonal to the plane containing the transmission and ground lines.

"In one embodiment of the invention, said part of the length of the interconnection device can be made flexible by at least one indent of the dielectric substrate over at least a portion of the length of the interconnection device.

"In one embodiment of the invention, said part of the length of the interconnection device can be made flexible by the production of the dielectric substrate in a flexible material, over at least a portion of the length of the interconnection device.

"In one embodiment of the invention, the interconnection device can make it possible to produce an interconnection of ground/signal/ground type, the interconnection device comprising a first and a second ground lines and a transmission line, the ground and transmission lines being produced on a face of the dielectric substrate.

"In one embodiment of the invention, the dielectric substrate can be defined in such a way that its expansion constant is less than or equal to the expansion constant of the transmission and ground lines.

BRIEF DESCRIPTION OF THE DRAWINGS

"Other features and advantages of the invention will become apparent on reading the description, given by way of example, based on the appended drawings which represent:

"FIGS. 1A, 1B, 1C, respectively a plan, profile and bottom view of an interconnection device according to an exemplary embodiment of the present invention, for the interconnection of two modules elements;

"FIG. 2, a bottom view of an interconnection device according to another embodiment of the invention;

"FIGS. 3A and 3B, respectively profile and bottom views of an interconnection device according to another exemplary embodiment of the present invention;

"FIGS. 4A, 4B and 4C, respectively a plan view illustrating three elements to be interconnected, the three elements interconnected by means of an interconnection device according to an exemplary embodiment of the invention, and a bottom view of the interconnection device in this example;

"FIG. 5, a profile synoptically illustrating an interconnection device according to another exemplary embodiment of the invention;

"FIGS. 6A and 6B, respectively a plan view and a bottom view of an interconnection device for two elements according to another exemplary embodiment of the invention;

"FIGS. 7A and 7B, respectively a plan view and a bottom view of an interconnection device for three elements according to another exemplary embodiment of the invention."

URL and more information on this patent application, see: DENIS, Stephane; LEDUC, Dominique; FORTEL, Julien; FOUIN, Patrick; BRIANTAIS, Didier. Interconnection Device for Electronic Circuits, Notably Microwave Electronic Circuits. Filed December 18, 2013 and posted July 3, 2014. Patent URL: http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.html&r=2911&p=59&f=G&l=50&d=PG01&S1=20140626.PD.&OS=PD/20140626&RS=PD/20140626

Keywords for this news article include: Thales, Aerospace and Defense Companies.

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Source: Defense & Aerospace Week


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