Laminated substrate for radio frequency device

Abstract

Laminated substrate for radio frequency device The present description relates to a laminated substrate (100) for a radio frequency device comprising successively: - a first metallic layer (110), in which is formed a first cavity (116) open at least partially on one of its sides, a feed line (400) extending in the first cavity (116), - a second metallic layer (120) in which is formed a second cavity (126) closed laterally, - a third metallic layer (130) in which is formed a third cavity (136) closed laterally, - a fourth metallic layer (140) in which is formed a fourth cavity (146) closed laterally, connection pads (500) being fixed on the fourth metallic layer (400), the second cavity (126), the third cavity (136) and the fourth cavity (146) forming a vertical RF feedthrough, a metallic plate (340) being positioned in the fourth cavity (316).Figure for the abridged version: Fig. 2A.

Description

Title of the invention: Laminated substrate for radio frequency device. Technical field

[0001] This description relates generally to substrates for electronic devices that emit and / or receive radio frequency signals. Such devices find applications, for example, in the field of automotive radar, for instance, in advanced driver assistance systems (ADAS). Previous technique

[0002] Typically, in AD AS devices, radio frequency signals (76 GHz–81 GHz) are transmitted and received by antennas. The transmission and reception delays are used to calculate the distance to the object. Then, several radars with image processing algorithms are used to identify the shape of the object. This type of system or function is called RADAR.

[0003] The devices can have several architectures. In devices with a launcher-on-package (LoP) architecture, a chip is placed on the top side of a bail grid array (BGA) substrate, itself mounted on a printed circuit board (PCB) with through-holes. An antenna guide module comprising an antenna and a waveguide is placed on the other side of the PCB.

[0004] Thus, signals can travel from the chip to the antenna module through the PCB.

[0005] To transmit a signal from the chip to the PCB, patch antennas, in the form of metal plates, are positioned on the underside of the BGA substrate and arranged to correspond with the through-holes in the PCB. They have a specific shape and size to resonate at the desired frequency. However, the RF connection through the BGA substrate and the antenna can result in both transmission loss and bandwidth loss. A shift and / or a decrease in frequencies may also be observed. A known solution to this problem is to create larger through-holes in the printed circuit board, which increases the size of the final device.

[0006] There is a need to improve signal transmission and / or increase signal bandwidth without increasing the size of the device. Summary of the invention

[0007] An embodiment overcomes all or part of the disadvantages of known devices.

[0008] One embodiment provides a stratified substrate for a radio frequency device comprising from a first main face to a second main face: - a first metallic layer in which a first cavity is formed, open at least partially on one of its sides, and a feed line, arranged coplanar to the first metallic layer and extending into the first cavity, - a second metallic layer in which a second laterally closed cavity is formed - a third metallic layer in which a third cavity, closed laterally, is formed - a fourth metallic layer in which a fourth laterally closed cavity is formed, the second cavity, the third cavity and the fourth cavity forming a vertical radio frequency pass-through in the substrate, a metallic plate being positioned at least in the fourth cavity.

[0009] According to one embodiment, an additional metal plate is positioned in the third cavity.

[0010] According to one embodiment, the additional metal plate positioned in the third cavity has different dimensions from the dimensions of the metal plate positioned in the fourth cavity.

[0011] According to one embodiment, another metal plate is positioned in the second cavity.

[0012] According to one embodiment, the first cavity, the second cavity, the third cavity and the fourth cavity have different dimensions.

[0013] According to one embodiment, the third cavity has dimensions smaller than the dimensions of the fourth cavity and larger than the dimensions of the second cavity.

[0014] According to one embodiment, the metal plate of the fourth cavity is positioned in the center of the fourth cavity.

[0015] According to one embodiment, the metal plate positioned in the fourth cavity is offset from the center of the fourth cavity.

[0016] Another embodiment provides for a radio frequency device comprising: - a stratified substrate as defined previously, - a radio frequency chip mounted on the first face of the laminated substrate, the radio frequency chip being connected to the power line, whereby the radio frequency chip is coupled to the vertical radio frequency feedthrough of the laminated substrate.

[0017] Another embodiment provides for a radio frequency signal transmission / reception system, comprising a radio frequency device as defined above, positioned on one face of a printed circuit board, an antenna module being disposed on a second face of the printed circuit board, the antenna module comprising waveguides and antennas coupled to the radio frequency device through holes passing through the printed circuit board substrate.

[0018] Another embodiment provides a method for manufacturing a laminated substrate as defined above, comprising the following steps: - deposit the second metallic layer and the third metallic layer on either side of the second dielectric layer, - to form cavities, closed laterally, in the second and third metallic layers, - deposit the first dielectric layer and the third dielectric layer on either side, respectively, of the second metallic layer and the third metallic layer, - to form the first metallic layer and the fourth metallic layer on either side, respectively, of the first dielectric layer and the third dielectric layer, - to form a cavity open on one side in the first metallic layer, and to form a cavity closed laterally in the fourth metallic layer, - position a metal plate in the cavity of the fourth metal layer, - form a power line, intended to be connected to a chip, the power line being coplanar to the first metal layer and extending into the first open cavity. Brief description of the drawings

[0019] These features and advantages, as well as others, will be described in detail in the following description of particular embodiments, given by way of non-limiting example, in relation to the accompanying figures, among which:

[0020] [Fig.1] is a schematic representation of a side view of a stratified substrate according to a particular embodiment;

[0021] [Fig.2A] and [Fig.2B] are schematic representations of a cross-sectional and side view of different stratified substrates according to two particular embodiments;

[0022] [Fig.3A], [Fig.3B], [Fig.3C], [Fig.3D] are schematic top-view representations, respectively, of the first metallic layer, the second metallic layer, the third metallic layer and the fourth metallic layer of a substrate, and [Fig.3E] is a schematic bottom-view representation of the fourth metallic layer and an oblong waveguide (for example 2.54 mm x 1 mm or 2.54 mm x 1.1 mm), according to another particular embodiment;

[0023] [Fig.4] is a schematic three-dimensional representation of a stratified substrate comprising the metallic layers of Figures 3A to 3D and the oblong waveguide of [Fig.3E];

[0024] [Fig.5A], [Fig.5B], [Fig.5C], [Fig.5D] are schematic top-view representations, respectively, of the first metallic layer, the second metallic layer, the third metallic layer and the fourth metallic layer of a substrate, and [Fig.5E] is a schematic bottom-view representation of the fourth metallic layer and an oblong waveguide (for example 2.54 mm x 1 mm), according to another particular embodiment;

[0025] [Fig.6] is a schematic three-dimensional representation of a stratified substrate comprising the metallic layers of Figures 5A to 5D and the oblong waveguide of [Fig.5E];

[0026] [Fig.7A], [Fig.7B], [Fig.7C], [Fig.7D] are schematic top-view representations, respectively, of the first metallic layer, the second metallic layer, the third metallic layer and the fourth metallic layer of a substrate, and [Fig.7E] is a schematic bottom-view representation of the fourth metallic layer and a thin oblong waveguide (for example 2.54 mm x 0.55 mm), according to another particular embodiment;

[0027] [Fig.8] is a schematic three-dimensional representation of a stratified substrate comprising the metallic layers of Figures 7A to 7D and the waveguide of [Fig.7E];

[0028] [Fig.9A], [Fig.9B], [Fig.9C], [Fig.9D] are schematic top-view representations, respectively, of the first metallic layer, the second metallic layer, the third metallic layer and the fourth metallic layer of a substrate, and [Fig.9E] is a schematic bottom-view representation of the fourth metallic layer and a thin oblong waveguide (for example 2.54 mm x 0.55 mm), according to another particular embodiment;

[0029] [Fig. 10] is a schematic three-dimensional representation of a stratified substrate comprising the metallic layers of Figures 9A to 9D and the waveguide of [Fig. 9E];

[0030] [Fig.llA], [Fig.llB], [Fig.llC], [Fig.llD] and [Fig.llE] are schematic and top-view representations of the third metallic layer of different substrates according to different particular embodiments;

[0031] [Fig.12A], [Fig.12B], [Fig.12C], [Fig.12D] and [Fig.12E] are schematic and top-view representations of the fourth metallic layer of different substrates according to different particular embodiments;

[0032] [Fig. 13A], [Fig. 13B], [Fig. 13C], [Fig. 13D] are schematic top-view representations, respectively, of the first metallic layer, of the second metallic layer, the third metallic layer and the fourth metallic layer of a substrate, and [Fig.13E] is a schematic representation, viewed from below, of the fourth metallic layer and an oblong waveguide (e.g. 2.54 mm x 1.05 mm), according to another particular embodiment;

[0033] [Fig.14A], [Fig.14B], [Fig.14C], [Fig.14D] are schematic top-view representations, respectively, of the first metallic layer, the second metallic layer, the third metallic layer and the fourth metallic layer of a substrate, and [Fig.14E] is a schematic bottom-view representation of the fourth metallic layer and a thin oblong waveguide (e.g. 2.54 mm x 0.55 mm), according to another particular embodiment;

[0034] [Fig. 14F] and [Fig. 14G] are schematic, three-dimensional representations, respectively, of a stack comprising the metallic layers of Figures 14A, 14B, 14C and 14D and of a stack comprising the metallic layers of Figures 14B, 14C and 14D (the first metallic layer of [Fig. 14A] not being shown here in order to better visualize the vertical RF crossing formed in the substrate);

[0035] [Fig.15A], [Fig.15B], [Fig.15C], [Fig.15D] are schematic top-view representations, respectively, of the first metallic layer, the second metallic layer, the third metallic layer and the fourth metallic layer of a substrate, and [Fig.15E] is a schematic bottom-view representation of the fourth metallic layer and a U-shaped waveguide (for example 1.6 mm x 1.0 mm), according to another particular embodiment;

[0036] [Fig. 16] is a schematic representation of a cross-sectional view of a radio frequency device, according to another particular embodiment;

[0037] [Fig. 17] is a schematic representation of a cross-sectional view of an RF signal transmission / reception system, according to another particular embodiment;

[0038] [Fig. 18] is a graph representing the simulations of the parameters SI 1, S22 and S21 as a function of frequency for two stratified substrates according to different particular embodiments;

[0039] the [Fig. 19] is a simulation of a Smith chart of the parameters SI 1 and S22 for two stratified substrates according to different particular embodiments;

[0040] [Fig.20] is a simulation representing the propagation of electromagnetic waves ('propagation of E-field') in a transmission / reception system according to a particular embodiment of the invention;

[0041] [Fig.21] is a graph representing the simulations of the parameters SI 1, S22 and S21 as a function of frequency for a stratified substrate according to another particular embodiment;

[0042] [Fig.22] is a simulation of a Smith chart of the parameters SI 1 and S22 for a stratified substrate according to another particular embodiment;

[0043] [Fig.23] is a simulation representing the propagation of electromagnetic waves ('propagation of E-field') in a transmission / reception system according to another particular embodiment of the invention;

[0044] [Fig.24], [Fig.25] and [Fig.26] are graphs representing the electrical performance obtained from different devices having substrates according to different particular embodiments.

[0045] The figures are not necessarily at a uniform scale in order to make them more legible. Description of the implementation methods

[0046] The same elements have been designated by the same reference numerals in the different figures. In particular, the structural and / or functional elements common to the different embodiments may have the same reference numerals and may have identical structural, dimensional and material properties.

[0047] For the sake of clarity, only the steps and elements useful for understanding the described embodiments have been shown and are detailed. In particular, the applications of the described embodiments and the uses of the antenna are not described.

[0048] Unless otherwise specified, when referring to two elements connected together, this means directly connected without intermediate elements other than conductors, and when referring to two elements connected (in English "coupled") together, this means that these two elements can be connected or linked through one or more other elements.

[0049] In the following description, when referring to absolute position qualifiers, such as "front", "back", "top", "bottom", "left", "right", etc., or relative position qualifiers, such as "above", "below", "superior", "inferior", etc., or to orientation qualifiers, such as "horizontal", "vertical", etc., unless otherwise specified, reference is made to the orientation of the figures. In particular, the term vertical propagation or vertical RF traversal refers to RF propagation or traversal along the z-axis.

[0050] Unless otherwise specified, the expressions "approximately", "roughly", and "in the order of" mean within 10%, preferably within 5%.

[0051] By between X and Y, we mean that the bounds X and Y are included.

[0052] The substrate which will be described subsequently can be used for applications Radio frequencies. Radio frequency (RF) refers to frequencies between 3 kHz and 300 GHz, and more specifically frequencies between 76 GHz and 81 GHz for the manufacture of AD AS type automotive radars. Although the description specifically mentions frequencies from approximately 76GHz to 81 GHz, other frequencies may be used for other devices using other radio frequencies.

[0053] We will now describe in more detail the stratified substrate 100 with reference to Figures 1, 2A and 2B, 3A to 3E, 4, 5A to 5E and 6, 7A to 7E and 8, 9A to 9E and 10, 1IA to 11E, 12A to 12E, 13A to 13E, 14A to 14G and 15A to 15E.

[0054] The stratified substrate 100 is a bead matrix substrate (also called BGA substrate for 'Bail Grid Array').

[0055] The substrate 100 comprises a first main face 101 and a second main face 102 (Figures 1, 2A and 2B).

[0056] The first main face 101 can be connected to one or more chips, and the second main face 102 can be assembled to a printed circuit board 700 (PCB). The second face 102 of the substrate 100 is covered with a matrix of beads 500. The beads 500 are connection pads that allow the substrate 100 to be fixed to an external device 700, for example, a printed circuit board. It is also possible to assemble two laminated substrates together, for example, by mirroring them (U-shaped structure).

[0057] The substrate 100 comprises at least four metallic layers 110, 120, 130, 140 from the first main face 101 to the second main face 102. The first metallic layer 110 is located on the side of the first face 101. The fourth metallic layer 140 is located on the side of the second face 102.

[0058] We will subsequently describe four metallic layers, but there could be more than four metallic layers (five or six, for example), for example by adding intermediate metallic layers between the aforementioned metallic layers.

[0059] The metallic layers 110, 120, 130, 140 may be made of a single metal or a metal alloy. They may, for example, be made of a material selected from gold, copper, aluminum, or a copper-aluminum alloy. The metallic layers 110, 120, 130, 140 may, for example, have a thickness of between 5 and 50 µm, preferably between 5 and 35 µm, and even more preferably between 15 and 25 µm. The metallic layers 110, 120, 130, 140 may, for example, have a thickness of 40 µm.

[0060] For example, the metallic layers 110, 120, 130, 140 are metallic sheets, in particular copper sheets.

[0061] The second metallic layer 120, the third metallic layer 130 and the fourth metallic layer 140 may have the same dimensions or different dimensions. Their surfaces may be square or rectangular.

[0062] The first metallic layer 110 may have a surface area smaller than the surface area of ​​the other metallic layers 120, 130, 140 (figures 3A, 5A, 7A, 9A for example).

[0063] The various metallic layers 110, 120, 130, 140 are positioned one above the other. The metallic layers 10, 120, 130, 140 are separated from each other by dielectric layers 210, 220, 230 in order to insulate them from each other.

[0064] A stack is obtained comprising alternating metallic layers 110, 120, 130, 140 and dielectric layers 210, 220, 230 (Figures 2A and 2B). The stack of the stratified substrate 100 comprises successively, from the first main face 101 to the second main face 102: - the first metallic layer 110 (figures 3A, 5A, 7A, 9A, 13A, 14A, 15A), - the first dielectric 210, - the second metallic layer 120 (figures 3B, 5B, 7B, 9B, 13B, 14B, 15B), - the second dielectric layer 220, - the third metallic layer 130 (figures 3C, 5C, 7C, 9C, 11A to 11E, 13C, 14C, 15C), - the third dielectric layer 230, - the fourth metallic layer 140 (figures 3D, 5D, 7D, 9D, 12A to 12E, 13D and 13E, 14D and 14E, 15D and 15E).

[0065] Additional dielectric layers 240, 260 can be arranged on either side of the stack described above in order to isolate the metallic layers 110, 140 (Figures 2A and 2B).

[0066] The dielectric layers 210, 220, 230, 240, 260 are made of a material that allows the transmission of the electromagnetic field. The dielectric layers 210, 220, 230, 240, 260 are, for example, formed of a so-called prepreg material. A prepreg material is understood to be a composite material comprising a thermoplastic polymer or a thermosetting resin and fillers, for example, glass fibers. The dielectric layers may also be made of ABF (Ajinomoto's Insulation Film®).

[0067] The second dielectric layer 220 forms the core of the stack and may be made of a different material than the other dielectric layers 210, 230, 240, 260. For example, it may be made of a resin containing fibers, particularly glass fibers, such as an epoxy resin containing glass fibers. It may also be made of a material known as FR-4 (Flame Retardant 4). The second dielectric layer 220 may have a thickness of between 100 and 150 µm.

[0068] Slots 116, 126, 136, 146 are formed in the metallic layers 110, 120, 130, 140 of each level. The second slot 126, the third slot 136, and the fourth slot 146 are aligned along the z-axis to form a vertical radio frequency feedthrough (also called an RF feedthrough). There is a 90-degree transition from Quasi-TEM mode (microstrip or transmission line) to TE mode (waveguide).

[0069] A cavity is defined as an area of ​​the metal layer in which there is an absence of material, thus creating a void extending through the entire thickness of the metal layer, thereby creating a passage or hole that connects the two opposite surfaces of the metal layer. Once the cavity 116, 126, 136, 146 is formed, this area can be filled with one or more materials. For example, this area can be filled, partially or totally, by the dielectric material of the lower or upper dielectric layer and / or by the adaptive element positioned within the cavity (in the center of the cavity or offset from the center of the cavity). The cavity 116, 126, 136, 146 preferably has at least four sides. It is, for example, rectangular. The cavity 126, 136, 146 is said to be laterally closed when all its edges are surrounded by the metal layer.Cavity 116 is said to be open when at least one of its edges is not formed by the metallic layer.

[0070] The first cavity 116 is formed in the first metallic layer 110. The first cavity 116 is an open cavity through which the transmission line 400 (also called the feed line) extends. The transmission line is arranged coplanar to the first metallic layer 110 (i.e., they are in the same xOy plane). The transmission line 400 is, for example, intended to be connected to the chip 610. The transmission line 400 is made of metal. It can be, for example, copper, aluminum, or gold. The transmission line 400 comprises a longitudinal element, such as a wire or ribbon, and an end. The end of the transmission line can be square, rectangular, or triangular. The length and width of the transmission line depend on the frequency.

[0071] At least a portion of the transmission line 400 is positioned in the first cavity 116. The end of the transmission line 400 and at least a portion of the longitudinal element are positioned in the cavity 116. The sides of the transmission line 400 are not in contact with the first metallic layer 110. The sides of the transmission line 400 are, for example, spaced from the edges of the cavity 116 by a distance of between 25 and 300 µm, for example, a distance of 40 µm, 50 µm, or 200 µm. For certain advanced technologies, it is possible to reduce the spacing to 10 or 12 microns, or even to 5 or 7 microns. The maximum spacing depends on the structure and position of the vias. For example, the spacing can be as small as a few millimeters. The various parameters are adjusted according to the frequency band and impedance.

[0072] According to a particular embodiment, the end of the transmission line 400 can be insulated from the metallic layer 110. In other words, the transmission line 400 extends into the first cavity 116, the sides and the end of the line of transmission not being in contact with the first metallic layer 110 (figures 3A, 4, 5A, 6, 7A, 8, 9A, 10).

[0073] According to another particular embodiment, the end of the transmission line 400 can be in contact with the first metallic layer 110 (Figures 13A, 14A and 15A). The end of the metallic layers can be terminated by a via block that forms a cavity.

[0074] In these different embodiments, the first metallic layer 110 and the transmission line 400 form a first level of the substrate 100 and play the role of impedance transformer. Indeed, the impedance of chip 610 is between 45 and 50 Ω, and the waveguide of printed circuit board 700 is between 100 and 600 Ω, or even between 200 and 600 Ω. The impedance arriving in the transmission line 400 is 45-50 Ω; it decreases, for example, to 11 Ω at the input of the substrate integrated waveguide (SIW), i.e., at the second cavity 126. At the output of the SIW of substrate 100, after passing through the fourth cavity 146, the impedance is compatible with that of printed circuit board 700, for example, 570 Ω. For illustration, impedances of 363 Ω and 169 Ω were obtained for waveguides measuring 2.54 mm x 1.1 mm, respectively. mm and 2.54 mm x 0.55 mm.

[0075] The orientation of the signal is also modified by 90° between the first cavity 116 and the second cavity 126 (represented by arrows in Figures 2A, 2B), subsequently allowing vertical propagation of the signal through cavities 136, 146.

[0076] The second metallic layer 120 includes a second cavity 126. The second cavity 126 is closed laterally. The second cavity 126 can be positioned opposite the transmission line 400 or offset from the position of the transmission line 400. For example, it is adjacent to the transmission line 400.

[0077] The third metallic layer 130 includes a third cavity 136 closed laterally.

[0078] The fourth metal layer 140 includes a fourth cavity 146 that is closed laterally. Connecting studs 500 (or beads) are positioned on the second face 102 of the substrate 100. They are fixed to the fourth metal layer 140. The connecting studs 500 form a stud matrix. There are no studs at the level of the fourth cavity 146.

[0079] At least the cavities 126, 136, 146 are positioned one above the other along the z-axis, so as to form a vertical RF feedthrough and to be able to transmit the radio frequencies from the chip 610 to the PCB 700. The vertical RF feedthrough thus passes through the different levels of the BGA 100 laminated substrate. This vertical RF feedthrough maximizes the bandwidth without increasing the size or insertion loss.

[0080] The second cavity 126, the third cavity 136 and the fourth cavity 146 have different dimensions from each other and / or can be offset from each other, at least part of the cavities overlapping along the z-axis to ensure a vertical RF crossing.

[0081] For example, the fourth cavity 146 has the largest dimensions and the first cavity 116 has the smallest dimensions.

[0082] The size of the cavity determines the frequency and the propagation field towards the waveguide (TE 10).

[0083] At least one cavity chosen from the second cavity 126, the third cavity 136 and the fourth cavity 146 includes a frequency matching element 320, 330, 340. Preferably, at least the fourth cavity 146 includes a matching element 340 (as for example shown in Figures 2A and Figures 2B).

[0084] In figures 3A to 10, an adaptation element 330 is positioned in the third cavity 136 and an adaptation element 340 can be positioned in the fourth cavity 146.

[0085] It is possible to have an adaptation element 330 positioned in the third cavity 136, an adaptation element 340 positioned in the fourth cavity 146 as well as an adaptation element in the second cavity 126 (figures 13A to 15E).

[0086] The frequency matching elements 320, 330, 340 may have different dimensions. The frequency matching elements comprise two main faces and lateral faces. The surface of each main face lies in the xOy plane.

[0087] Depending on the desired characteristics, the frequency matching elements can be positioned in the center of the cavity or on the edges of the cavity and / or have different shapes. The matching elements are not necessarily aligned with each other.

[0088] The frequency adaptation elements 320, 330, 340 are configured to channel the electromagnetic signal into the cavities 126, 136, 146.

[0089] The adaptation elements 320, 330, 340 can be arranged in a staggered pattern to increase the bandwidth.

[0090] The adaptation elements 320, 330, 340 can partially overlap one another (along the z-axis).

[0091] According to one embodiment, the frequency matching element 320, 330, 340 can be a plate ('patch') isolated from the edges of the cavity 126, 136, 146 by a gap ([Fig. 2A], Figures 3A to 6). The plate is, for example, a metallic plate. For example, it is a copper plate. The plate can be made of the same material as the metallic layer. The plates are preferably made of a conductive material, preferably in a metal, for example copper, aluminium, a copper and aluminium alloy or gold.

[0092] The plates are, for example, rectangular or square. They could also be circular.

[0093] The plates can have the same thickness as the metallic layers or an identical thickness to within 10% or even 5%.

[0094] According to another embodiment, the impedance matching element 320, 330, 340 can be a portion of the metal layer that protrudes into the cavity ([Fig. 2B], Figures 7A to 12E, Figures 13A to 15E). In other words, a portion of the metal layer extends into the cavity and forms a projection or protrusion in the cavity 126, 136, 146. The protruding portion forms an internal extension of the metal plate.

[0095] It goes without saying that if the adapting element is a part of the metallic layer protruding into the cavity, the adapting element will be positioned on the edge of the cavity or in a corner of the cavity.

[0096] The protruding parts are, for example, rectangular or square. The protruding parts have the same thickness as the metallic layers.

[0097] The irregular shapes of the protruding parts and / or the cavity allow the frequency and bandwidth to be matched.

[0098] By way of illustration and not limitation, figures 11A to 11Ea represent several possible configurations of a third metallic layer 130, a part of which 330 protrudes into the cavity 136.

[0099] By way of illustration and not limitation, figures 12A to 12E represent several possible configurations of a fourth metallic layer 140, a part of which 340 protrudes into the cavity 146.

[0100] These embodiments can be combined. It is possible within the same device to use plates for one or more levels and protruding parts for one or more levels.

[0101] The stack also includes interlayer metal vias 250 formed through some or all of the stack layers so as to connect different metal layers 110, 120, 130, 140 to each other. The various interlayer metal vias allow at least two metal layers to be connected together. They can connect more than two metal layers (for example, three or four metal layers). The interlayer metal vias 250 can be stacked or offset from each other.

[0102] At least one row of vias 115, 125, 135, 145, formed in each metallic layer 110, 120, 130, and 140, surrounds the cavities 116, 126, 136, and 146, respectively. The rows of vias 115, 125, 135, and 145 help to confine the electromagnetic waves within the cavity 116, 126, 136, and 146 and / or prevent signal leakage. The different rows of vias 115, 125, 135, and 145 are positioned one above the other along the z-axis. It is possible to have several rows of vias 115, 125, 135, 145 per metallic layer 110, 120, 130, 140.

[0103] The conductive layers 110, 120, 130, 140 and the conductive vias 115, 125, 135, 145 form a waveguide-like structure, for example rectangular in shape. The RF signal is confined and guided through the substrate between the conductive plates, with the vias 115, 125, 135, 145 acting as side walls.

[0104] The use of a layered substrate 100 comprising cavities 116, 126, 136, 146 of different dimensions and / or offset from each other and / or cavities 116, 126, 136, 146 comprising frequency matching elements 320, 330, 340 of different dimensions and / or offset from each other leads to obtaining a wide, broadband, low-loss RF feedthrough at the desired frequencies. This stacking allows adaptation to the entire desired radio frequency band (in particular 76 GHz - 81 GHz).

[0105] Moreover, with such a substrate 100, it is possible to obtain a slightly wider bandwidth than the frequency range classically used in automotive radars (76GHz - 81GHz), which makes it less sensitive to manufacturing.

[0106] It is possible to dimension the cavities 116, 126, 136, 146 and the adaptation elements 320, 330, 340 according to the working frequency and / or the substrate.

[0107] The size of the device is reduced compared to conventional technologies, particularly those using patch antennas. Complete integration into the substrate 100 is achieved.

[0108] The thickness of the substrate 100 is, for example, less than between 100 and 900 pm, for example between 100 and 200 pm, for example on the order of 150 pm, or between 200 and 300 pm.

[0109] This compact and efficient feedthrough can be produced using standard 100 laminated substrate technology. Costs are thus reduced.

[0110] The substrate 100 described above can be used in a radio frequency device ([Fig. 16]) or an RF signal transmission / reception system ([Fig. 17]).

[0111] The radio frequency device includes the laminated substrate 100 and a housing 600 comprising at least one electronic component and, in particular, at least one radio frequency component 610 molded in an insulating material 620, such as a polymer or a resin.

[0112] The radio frequency component 610 is an electronic component capable of transmitting and receiving specific radio frequency signals.

[0113] In particular, the radio frequency component 610 is a radio frequency chip 610.

[0114] The 610 chip has front-side connection pads covered by metallized pads ('bumps'; not shown). The metallized pads are, for example, made of tin or a tin-based alloy.

[0115] The radio frequency component 610 is assembled on the substrate 100.

[0116] The chip 610 is mounted directly onto the BGA laminated substrate 100, with the bumps of the chip 610 oriented towards the first face 101 of the substrate 100 ('flip-chip'). The chip 610 is connected to the BGA substrate by its bumps. It could be attached to the substrate by wire bonding.

[0117] The chip 610 is connected to the transmission line 400 of the substrate 100, for example by means of microstrips.

[0118] The RF signal transmission / reception system includes the radio frequency device, positioned on a first face 701 of a printed circuit board 700 (PCB or 'printed circuit board'), and an antenna module 800 arranged on a second face 702 of the printed circuit board 700.

[0119] The antenna module 800 comprises a substrate 810 in which a waveguide 820 and antennas 830 are formed.

[0120] The printed circuit board 700 used is, for example, manufactured by forming through holes 710 in the substrate 700 and metallizing them. The side walls 730 of the through holes 710 confine the electromagnetic waves. The upper and lower surfaces of the substrate 700 can also be metallized to form the waveguide.

[0121] The antenna module 800 is coupled to the radio frequency device through the holes 710 through the printed circuit 720. The signal is transmitted continuously from the chip 610 to the PCB 700 then to the waveguide 820 and to the antenna 830 of the antenna module 800.

[0122] The BGA substrate 100 is fixed to the printed circuit board 700. In particular, the BGA balls 500 are brazed onto the printed circuit board 700. The BGA balls 500 are, for example, made of tin or a tin alloy, such as SAC (tin, silver and copper alloy).

[0123] Part of the 500 balls of the BGA acts as a short waveguide to transmit the signal to the PCB 700.

[0124] The signal is thus routed through the BGA substrate 100, via the vertical RF feedthrough, to the holes 710 formed in the printed circuit board 700 and then to the antenna module 800.

[0125] Substrate 100 can be manufactured according to the following steps: - deposit the second metallic layer 120 and the third metallic layer 130, on either side of the second dielectric layer 220, - to form cavities 126, 136, closed laterally in the second metallic layer 120 and the third metallic layer 130, - deposit the first dielectric layer 210 and the third dielectric layer 230 on either side of the previously deposited metallic layers 120, 130, - form the first metallic layer 110 and the fourth metallic layer 140 on either side of the first dielectric layer 210 and the third dielectric layer 230, - to form a cavity 116 open on one of its sides in the first metallic layer 110, and to form a cavity 146 closed laterally in the fourth metallic layer 140, - form a 400 power line, intended to be connected to a chip, the 400 power line extending into the open cavity 116.

[0126] The cavities 116, 126, 136, 146 can be formed, for example, by microfabrication techniques such as lithography and etching.

[0127] The cavities 116, 126, 136, 146 have different dimensions. The closed cavity 146 of the fourth metallic layer 140 has the largest dimensions and the open cavity 116 of the first metallic layer 110 has the smallest dimensions.

[0128] If the device includes one or more adaptation elements in the form of a metal plate, the method will also include one or more steps in which the metal plate(s) are positioned in the corresponding cavities.

[0129] The method may also include a step in which connecting pads 500 are fixed to the fourth metallic layer.

[0130] Illustrative and non-limiting examples

[0131] Example 1 and example 2: substrates with metallic plates ('patch') in cavities

[0132] In a first example, the BGA 100 substrate is formed from the different elements shown in Figures 3A to 3E and 4. A metal plate is disposed in the third metal layer 130 and in the fourth metal layer 140.

[0133] In a second example, the BGA 100 substrate is formed from the different elements shown in Figures 5A to 5E and 6. A metal plate is disposed in the third metal layer 130 and in the fourth metal layer 140.

[0134] The main differences between the two examples are as follows: - The 400 connection line of the first level is different, and the spaces between the 400 transmission line and the first cavity 116 are different; this allows the bandwidth to be adapted. - the second cavity 126 is smaller in example 2 than that of example 1 in order to obtain a higher frequency resonance, - the fourth cavity 146 is wider in example 2 than that of example 1, and the plate 340 of the fourth cavity 146 is offset in example 2 to obtain a resonance at a lower frequency.

[0135] The third level of example 2 is identical to that of example 1.

[0136] In each example, a PCB 700 is assembled to the BGA 100 substrate. The PCB 700 features 710 oblong through holes of 2.54 mm x 1.1 mm acting as a waveguide to the antenna module.

[0137] A 400 transmission line is connected to a chip ('bump'), positioned on the BGA substrate, and is connected to the SIW waveguide ('Substrate integrated waveguide').

[0138] The performance of the two devices was simulated (figures 18 to 20).

[0139] In the first example, the following performance is obtained: -12 dB / -SI 1 (76 GHz-81 GHz).

[0140] In the second example, the following performance is obtained: -15 dB / Sll (76 GHz - 81 GHz), S21: -1.05 dB more flexibility on S11 / S22 (less than -10 dB) thanks to the bandwidth expansion.

[0141] Both examples exhibit good performance.

[0142] The device of Example 1 has a narrow bandwidth adaptation to the operating bandwidth compared to version 2.

[0143] The device in Example 2 exhibits better adaptation from the input, which slightly improves performance in the lower and upper bands.

[0144] However, it should be noted that both Example 1 and Example 2 operate at the desired frequencies (76 GHz - 81 GHz) and have the expected performance.

[0145] Example 3: substrate with metal plates, part of which protrudes into cavities ('slot')

[0146] In a third example, the BGA 100 substrate is formed from the different elements shown in Figures 9A to 9E and 10. A part 330 of the third metal layer 130 and a part 340 of the fourth metal layer 140 protrude, respectively, into the third cavity 136 and into the fourth cavity 146.

[0147] Compared to examples 1 and 2, the device in example 3 has a size reduction of about 34%.

[0148] A PCB 700 is assembled to the BGA 100 substrate. The PCB 700 has oblong through holes 710 measuring 2.54 mm x 0.55 mm which act as waveguides to the antenna module. The size of the waveguide is considerably reduced (by approximately 50% along the length of the oblong portion).

[0149] The device's performance was estimated by simulating the S parameters, or scattering parameters. These parameters reflect the transmission and reflection properties of high-frequency networks. S1 and S22 are less than -10 dB, and S21 is -0.96 dB: the resulting device exhibits good performance (Figures 21 to 23). EM wave propagation shows no energy loss to the outside of the device.

[0150] With an RF signal extension of 400 pm in length and a width between 160 and 180 pm and a die escape extension of 120 and 155 pm in length and a width of 30 pm, the following characteristics are obtained: SU: -23 to -20dB at 76GHz -81GHz (Specification: -20dB min); S21: -1.2dB to -1.4dB at 76GHz -81GHz (Specification: -1.5dB max).

[0151] Example 4: substrate with metal plates, part of which protrude into cavities ('slot')

[0152] The performance of the devices shown in Figures 13A to 13E, 14A to 14F, and 15A to 15E was simulated. The results obtained are shown in Figures 24 to 26, respectively. They demonstrate that a very wide bandwidth is achieved in the desired frequency range. This reduces the sensitivity due to manufacturing tolerances.

[0153] Performances of SI 1 and S22 below -30 dB and of S12 and S21 above -0.5 dB can be achieved.

[0154] Various embodiments and variations have been described. A person skilled in the art will understand that certain features of these various embodiments and variations could be combined, and other variations will become apparent to a person skilled in the art.

[0155] Finally, the practical implementation of the embodiments and variants described is within the reach of a person skilled in the art, based on the functional indications given above.

Claims

Demands

1. A laminated substrate (100) for a radio frequency device comprising, from a first main face (101) to a second main face (102): - a first metallic layer (110) in which is formed a first cavity (116) open at least partially on one of its sides, and a feed line (400), arranged coplanar to the first metallic layer (110) and extending into the first cavity (116), - a first dielectric layer (210), - a second metallic layer (120) in which is formed a second cavity (126) closed laterally, - a second dielectric layer (220), - a third metallic layer (130) in which is formed a third cavity (136) closed laterally, - a third dielectric layer (230), - a fourth metallic layer (140) in which is formed a fourth cavity (146) closed laterally, the second cavity (126),the third cavity (136) and the fourth cavity (146) forming a vertical radio frequency pass-through in the substrate (100), a metal plate (340) being positioned at least in the fourth cavity (316).

2. Substrate according to claim 1, wherein an additional metal plate (330) is positioned in the third cavity (136).

3. Substrate according to the preceding claim, wherein the additional metal plate (330) positioned in the third cavity (136) has different dimensions from the dimensions of the metal plate (340) positioned in the fourth cavity (146).

4. Substrate according to any one of the preceding claims, wherein another metal plate (320) is positioned in the second cavity (126).

5. Substrate according to any one of the preceding claims, wherein the first cavity (116), the second cavity (126), the third cavity (136) and the fourth cavity (146) have different dimensions.

6. Substrate according to any one of the preceding claims, wherein the third cavity (136) has dimensions smaller than the dimensions of the fourth cavity (146) and greater than the dimensions of the second cavity (126).

7. Substrate according to any one of claims 1 to 6, wherein the metal plate (340) of the fourth cavity is positioned at the center of the fourth cavity (136).

8. Substrate according to any one of claims 1 to 6, wherein the metal plate (340) positioned in the fourth cavity (146) is offset from the center of the fourth cavity (146).

9. Radio frequency device comprising: - a laminated substrate (100) as defined in any one of claims 1 to 8, - a radio frequency chip (610) mounted on the first face (101) of the laminated substrate (100), the radio frequency chip (610) being connected to the power line (400), whereby the radio frequency chip (610) is coupled to the vertical radio frequency feedthrough of the laminated substrate (100).

10. Radio frequency signal transmission / reception system, comprising a radio frequency device as defined in claim 9, positioned on a first face (701) of a printed circuit board (700), an antenna module (800) being disposed on a second face (702) of the printed circuit board (700), the antenna module (800) comprising waveguides (820) and antennas (830) coupled to the radio frequency device by means of holes (710) passing through the substrate (710) of the printed circuit board (700).

11. A method for manufacturing a laminated substrate (100) as defined in any one of claims 1 to 8 comprising the following steps: - depositing the second metal layer (120) and the third metal layer (130) on either side of the second dielectric layer (220), - forming laterally closed cavities (126, 136) in the second metal layer (120) and the third metal layer (130), - depositing the first dielectric layer (210) and the third dielectric layer (230) on either side, respectively, of the second metal layer (120) and the third metal layer (130), - to form the first metallic layer (110) and the fourth metallic layer (140) on either side, respectively, of the first dielectric layer (210) and the third dielectric layer (230), - to form a cavity (116) open on one of its sides in the first metallic layer (110), and to form a cavity (146) closed laterally in the fourth metallic layer (140), - position a metal plate (340) in the cavity (146) of the fourth metal layer (140), - form a power line (400), intended to be connected to a chip, the power line (400) being coplanar to the first metallic layer (110) and extending into the first open cavity (116).

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