MONOLITHIC MICROWAVE INTEGRATED CIRCUIT

Abstract

The invention relates to a microwave module comprising a microwave chip comprising a substrate, an active layer on a first face of the chip, an electrical ground layer on a second face opposite the first face, the active layer comprising microstrip guide transmission lines; a package encapsulating the microwave chip, said package comprising a redistribution layer covering the active layer of the microwave chip and comprising electrical connection traces for a connection between the active layer and an electrical interface of the microwave module;said active layer comprising at least one transistor, one or more of the electrical traces of the redistribution layer, called ground traces, connecting a source electrode of the transistor to one or more of the electrical interfaces, called ground interfaces, said ground interface(s) being configured to be connected to a ground of an electronic card.;

Description

Title of the invention: MONOLITHIC MICROWAVE INTEGRATED CIRCUIT

[0001] The invention relates to a microwave module comprising a microwave chip. The invention further relates to an assembly comprising a microwave module according to the invention and an electronic card.

[0002] Microwave chips or MMIC circuits (for "Monolithic Microwave In-tegrated Circuit" in English) are circuits made using microelectronics techniques. They are used, for example, in radars to increase the power of the signal emitted by the antenna, for example from a few mW to around 100W.

[0003] [Fig.l] shows an example of a known microwave module 1 mounted on an electronic card 2. The microwave module 1 is attached to an electronic card 2. The microwave module 1 comprises a microwave chip 110 encapsulated in a housing 120. The chip 110 comprises a substrate 113, a first face comprising an active layer 111 and a ground layer 112 on a second face opposite the first face. The active layer 111 comprises the active components of the microwave chip 110, such as a transistor 114 for example, and the passive components of the microwave chip 110, such as capacitors or inductors. The active layer 111 also comprises transmission lines allowing the propagation of radiofrequency signals from or to the components of the active layer 111.The transmission lines may form microstrip transmission lines allowing the propagation of a positive polarity of the radiofrequency signal, while the ground layer 112 allows the propagation of a negative polarity of the radiofrequency signal. After its manufacture, the microwave chip 110 is encapsulated in the housing 120 by a fan-out wafer level packaging technique or FOWLP (Fan-Out Wafer Level Packaging) known per se. The housing 120 comprises in particular a plastic molding 122 covering the second face and the sides of the microwave chip 110, in particular for mechanical protection of the microwave chip 110. The housing 120 further comprises a redistribution layer or RDL (Redistribution Layer) 124.The RDL layer 124 covers the active layer 111 and allows the terminals of the microwave chip 110 to be connected to external components. The terminals of the microwave chip are typically located at the edge of the active layer 111. For this purpose, the RDL layer 124 comprises electrical connection traces 125, 126. These electrical connection traces 125, 126 lead to interfaces 128 of the package 120, which are . including marbles (or “bump” in English).

[0004] Typically, the microwave module 1 is mounted on the electronic card 2 so that the first face of the microwave chip 110 is oriented towards the electronic card 2. The interfaces 128 make it possible to connect the connection traces 125, 126 of the RDL layer 124 with tracks 25, 26 of the electronic card 2. Connection traces 126 then allow the exchange of radiofrequency signals between the microwave chip 110 and tracks 26 of the electronic card 2.

[0005] However, it is necessary to connect the ground 112 of the microwave chip 110 with that of the electronic card 2. For this purpose, the microwave chip 110 comprises electrical connection vias 117 connecting the ground 112 to a terminal on the first face of the chip 110. Connection traces 125 connect these terminals to interfaces 128. The connection to the ground 22 of the electronic card 2 comprises tracks 25 on the surface of the electronic card 2, which are connected to the ground 22 by means of electrical connection vias 27.

[0006] Furthermore, the source electrode 114', 114” of the transistor 114 is connected to the ground 112 via electrical connection vias 117. A current flowing through the source electrode 114', 114”, in particular a closing current of the transistor 114, must flow through the electrical connection vias 117, the ground layer 122 of the chip 110, the electrical connection vias 117 and the connection traces 125, before arriving at the interfaces 128. Such an electrical path corresponds to additional impedances which will increase the equivalent impedance at the source electrode 114', 114” of the transistor 114. This reduces the frequency performance of the transistor 114 compared to an assembly where the second face of the chip 110 would be mounted oriented towards the electronic card 2.

[0007] US patent publication US 11557545 B2 discloses an MMIC circuit mounted on an electronic card such that the active layer is oriented towards the electronic card. The microwave chip includes an additional ground layer between the active layer and the RDL layer of the package, which complicates the manufacture of the assembly consisting of the MMIC circuit and the package.

[0008] A microwave module is therefore sought which allows mounting on an electronic card with the active layer oriented towards said electronic card, with a short and simple ground connection between the microwave module and the electronic card.

[0009] To this end, the invention proposes a microwave module comprising: • a microwave chip comprising a substrate, an active layer on a first face of the chip, an electrical ground layer on a second face opposite the first face, the active layer comprising microstrip guide transmission lines; • a package encapsulating the microwave chip, said package comprising a redistribution layer covering the active layer of the microwave chip and comprising electrical connection traces for a connection between the active layer and an electrical interface of the microwave module; said active layer comprising at least one transistor, one or more of the electrical traces of the redistribution layer, called ground traces, connecting a source electrode of the transistor to one or more of the electrical interfaces, called ground interfaces, said ground interface(s) being configured to be connected to a ground of an electronic card.

[0010] Thanks to the ground traces and the ground interfaces, the electrical path between the source electrode of the transistor and the electrical ground of the electronic card is shorter than in the prior art of [Fig.l]. The connection between the source electrode and the ground of the electronic card being more direct, the additional inductances are reduced compared to the prior art, which improves the frequency performance of the transistor. The connection to the ground of the source electrode uses electrical traces of the redistribution layer, without the need for an additional ground layer between the active layer and the redistribution layer.

[0011] According to one embodiment, the ground interface(s) and the ground trace(s) are arranged symmetrically with respect to said transistor.

[0012] According to one embodiment, the source electrode comprises two parts located on either side of the transistor, said ground trace(s) connecting said parts to said ground interface(s).

[0013] According to a variant, the source electrode is connected to a single ground interface, the parts of the source electrode being connected to said ground interface.

[0014] According to a variant, the parts of the source electrode are connected to said ground interface via the same ground trace or via respective ground traces.

[0015] According to a variant, the source electrode is connected to several ground interfaces, the parts of the source electrode being connected to said ground interfaces.

[0016] According to a variant, each part of the source electrode is connected to a respective ground interface via a respective ground trace.

[0017] According to a variant, the parts of the source electrode are connected to the ground interfaces via the same ground trace.

[0018] According to one embodiment, the microwave chip further comprises an electrical connection between the source electrode of the transistor and the electrical ground layer of the chip, through the substrate of the microwave chip.

[0019] The invention also relates to an assembly comprising: • a microwave module according to the invention, • an electronic card comprising an electrical ground layer, said microwave module being mounted on the electronic card so that the active layer of the chip is oriented towards said electronic card, said ground interface(s) being electrically connected to the ground of the electronic card.

[0020] According to one embodiment, the microwave module is mounted on the electronic card, one face of the microwave module, comprising said ground interface(s), being opposite the electronic card, so that said ground interface(s) come against a terminal of the electronic card.

[0021] Other characteristics and advantages of the present invention will appear more clearly on reading the description which follows in relation to the following appended figures:

[0022] [Fig-1]: [Fig.l], already described, illustrates a prior art microwave module mounted on an electronic card;

[0023] [Fig.2]: [Fig.2] illustrates an example of a microwave module according to the invention mounted on an electronic card;

[0024] [Fig.3]: [Fig.3] represents a transistor of the example of microwave module of [Fig.2];

[0025] [Fig.4]: [Fig.4] illustrates another example of a microwave module according to the invention;

[0026] [Fig.5]: [Fig.5] illustrates yet another example of a microwave module according to the invention;

[0027] [Fig.6]: [Fig.6] illustrates yet another example of a microwave module according to the invention.

[0028] [Fig. 2] represents an example of a microwave module 200 according to the invention. The microwave module 200 comprises a microwave chip 210. The microwave chip 210 comprises an active layer 211 on a first of its faces, a substrate 213, and an electrical ground layer 212 on a second face opposite the first. In particular, the active layer 211, the substrate 213, and the ground layer 212 form a stack in which the layers are superimposed in this order. In particular, the active layer 211 comprises the active components of the microwave chip 210, such as a transistor for example, and the passive components of the microwave chip 210, such as capacitors or inductors. The active layer 211 also comprises transmission lines allowing in particular the propagation of radiofrequency signals from or to the components of the active layer 211.The transmission lines form microstrip transmission lines allowing the propagation of a positive polarity of the radiofrequency signal, while the ground layer 212 allows the propagation of a . negative polarity of the radio frequency signal. The active layer 211 comprises at least one transistor 214.

[0029] A housing 220 encapsulates the microwave chip 210. The housing 220 comprises a redistribution layer (“RDL layer” in the following) 224 which covers the active layer 211, in particular by coming into direct contact with the active layer 211. The RDL layer 224 makes it possible in particular to connect terminals of the microwave chip 210, in particular of the active layer 211, with external components. The RDL layer 224 comprises electrical connection traces 225, 226, 227 for a connection between the active layer 211 and an electrical interface 228 of the microwave module 200. An electrical trace 227 of the RDL layer 224, called a ground trace, connects a source electrode 214', 214” of the transistor 214 to an electrical interface 229, called a ground interface. The ground interface 229 is configured to be connected to a ground 322 of an electronic card 300.

[0030] In particular, the microwave module 200 is mounted on the electronic card 300 so that the active layer 211 of the chip 210 is oriented towards the electronic card 300. The ground interface 229 can then be electrically connected to the ground 322 of the electronic card 300.

[0031] For this purpose, the electrical card 300 comprises in particular a terminal 325, in particular an electrical track, on its face oriented towards the microwave module 200, against which the ground interface 229 comes into contact. In particular, the electrical ground 322 of the electronic card 300 is on an opposite face of the electronic card 300. The terminal 325 can then be in electrical contact with the electrical ground 322 of the electronic card 300 by means of an electrical connection via 327.

[0032] Thanks to the ground trace 227 and the ground interface 229, the source electrode 214', 214” of the transistor 214 is connected to the ground 322 of the electronic card 300 following a more direct electrical path compared to the prior art, which reduces the equivalent inductance at the source electrode 214', 214” and makes it possible to improve the frequency performance of the transistor 214 compared to the prior art.

[0033] The electrical ground 212 of the microwave chip 210 is connected to an interface 228 of the microwave module 200, in particular by means of an electrical connection via 217 passing through the substrate 213 of the microwave chip 210 to a terminal of the chip 210 on the first face of the chip 210. A trace 225 of the RDL layer 224 can then connect this terminal with the interface 228 of the microwave module 200. The interface 228 of the microwave module 200 can then be in electrical connection with the electrical ground 322 of the electronic card 300, in particular in a similar manner to the connection of the ground interface 229 with the ground 322 of the electronic card 300. Thus, the ground 212 of the microwave chip 210 can be connected with that 322 of the electronic card 300.

[0034] According to one embodiment, the source electrode of the transistor 214 comprises a first portion 214' and a second portion 214” located on either side of the transistor 214. [Fig. 3] shows a schematic perspective view of the transistor 214. In particular, the transistor 214 comprises a gate electrode G, through which a radiofrequency signal can be received; and the transistor 214 comprises a drain electrode D through which a radiofrequency signal can be emitted. Each portion 214', 214” can then be connected to one or more ground interfaces 229 via one or more ground traces 227.

[0035] The microwave chip 210 may comprise an electrical connection between the source electrode 214', 214” of the transistor 214 and the electrical ground layer 212 of the chip 210. Such an electrical connection may pass through the substrate 213 of the microwave chip 210, in particular via electrical connection vias 217. This electrical connection provides an additional electrical path making it possible to further reduce the equivalent inductance at the source electrode 214', 214”. In particular, each portion 214', 214” may be connected to the electrical ground layer 322 of the chip 320 via one or more respective electrical connection vias 217. [Fig. 3] shows one electrical connection via 217 per portion 214', 214” of the source electrode. However, each part 214', 214” could be connected to the electrical ground layer 322 by four electrical connection vias for example.The electrical connection via 217 is for example a metallized hole.

[0036] The chip 210 is notably manufactured using microelectronics processes. In particular, after its manufacture, the first face and the second face of the chip 210 each form an external face of the chip 210.

[0037] After its manufacture, the microwave chip 210 is in particular encapsulated in the housing 220 by a wafer-level packaging technique or FOWLP (for “Fan-Out Wafer Level Packaging” in English) known per se. Referring again to [Fig. 2], the housing 220 comprises in particular a plastic molding 222 covering the second face and the sides of the microwave chip 210, in particular for mechanical protection of the microwave chip 210. The plastic molding 222 may be made of an epoxy material. In particular, the RDL layer 224 forms a layer coming against the active layer 211, and rests by its edges against a part of the plastic molding 222. The RDL layer 224 may comprise a first passivation sub-layer, coming in particular against the active layer 211; a second sub-layer comprising the electrical connection traces 225, 226, 227; and a third passivation sub-layer.Passivation undercoats are, for example, made of an electrically insulating material. The first undercoat of . passivation may comprise windows allowing contact between the electrical terminals of the active layer 211 and the electrical connection traces 225, 226, 227. The third passivation sub-layer may comprise windows allowing contact between the electrical connection traces 225, 226, 227 and the interfaces 228, 229, 230. In particular, electrical connection traces 226 allow the exchange of radiofrequency signals between the microwave chip 210 and tracks 326 of the electronic card 300. For this purpose, the connection traces 226 may be connected to interfaces 230 which come into electrical contact with the electronic card 300.

[0038] The interfaces 228, 229, 230 of the housing 220 make it possible in particular to electrically connect the microwave module 200, in particular the active layer 211 of the microwave chip 210, with its environment. The interfaces 228, 229, 230 are for example balls (or “bumps” in English). The interfaces 228, 229, 230 are in particular on a face of the microwave module 200 which is parallel to the first face of the microwave chip 210. In particular, the interfaces 228, 229, 230 come against the surface of the electronic card 300 when the microwave module 200 is mounted on the electronic card 300 so that the active layer 211 of the microwave chip 210 is oriented towards the electronic card 300.

[0039] In the example of microwave module 200 illustrated in [Fig.2], the source electrode 214', 214” is connected to a single ground interface 229. Each part 214', 214” of the source electrode is connected to the ground interface 229 via the same ground trace 227. In particular, the ground trace 227 forms a straight segment connecting the two parts 214', 214” of the source electrode. The interface 229 is in particular connected to the ground trace 227 at its midpoint.

[0040] [Fig.4] illustrates an example of a microwave module 400 identical to that illustrated in [Fig.2], except that the source electrode 414', 414” is connected to several ground interfaces 429', 429”. Each portion 414', 414” of the source electrode is connected to a respective ground interface 429', 429” via a same ground trace 427. In particular, the ground trace 427 forms a straight segment connecting the two portions 214', 214” of the source electrode. In particular, a first interface 429' is connected to one end of the ground trace 427 located on the side of the first portion 414' of the source electrode; and a second interface 429” is connected to one end of the ground trace 427 located on the side of the second portion 414” of the source electrode.Each ground interface 429', 429” can connect with a respective terminal, in particular a respective electrical track 325', 325”, of the electronic card 300 which is connected to the electrical ground 322 of the electronic card 300 via a respective electrical connection via 327', 327”.

[0041] [Fig. 5] illustrates an example of a microwave module 500 identical to that illustrated in [Fig. 4], except that each portion 514', 514” of the source electrode is connected to a respective ground interface 529', 529” via a respective ground trace 527', 527”. In particular, each ground trace 527', 527” extends from the respective portion 514', 514” of the source electrode, in particular along a straight line connecting the portions 514', 514” of the source electrode. However, the ground traces 527', 527” could extend in a different direction, for example a direction perpendicular to the straight line connecting the two portions 514', 514” of the source electrode.In particular, a first interface 529' is connected to one end of a first ground trace 527' connected to the first portion 514' of the source electrode; and a second interface 529” is connected to one end of a second ground trace 527” connected to the second portion 514” of the source electrode. Each ground interface 529', 529” can connect with a respective terminal, in particular a respective electrical track 325', 325”, of the electronic card 300 which is connected to the electrical ground 322 of the electronic card 300 via a respective electrical connection via 327', 327”.

[0042] In the examples illustrated in Figures 2, 4 and 5, the ground traces and the ground interfaces are preferably arranged symmetrically with respect to the transistor. This allows for equivalent inductances at the parts of the source electrode that are equal. However, the ground trace(s) and the ground interface(s) could be arranged asymmetrically with respect to the transistor. This is the case, for example, when the size of the microwave module does not allow for a symmetrical arrangement.

[0043] [Fig. 6] illustrates an example of a microwave module 600 identical to that illustrated in [Fig. 2], except that the ground trace 627 and the interface 629 are arranged asymmetrically with respect to the transistor. In particular, the ground trace 627 forms a straight segment connecting the two parts 614', 614” of the source electrode. The interface 629 is notably connected to one end of the ground trace 627.

[0044] The connection of the source electrode to the ground 322 of the electronic card 300 via the ground trace(s) of the RDL layer and the ground interface(s) can further improve the heat dissipation of the transistor. Indeed, by being connected to the source electrode, the ground trace(s) are connected as close as possible to the heating zone of the transistor. The improvement in heat dissipation is particularly obtained when the cooling of the assembly comprising the microwave module and the electronic card 300 is obtained by means of a heat sink mounted on the ground 322 of the electronic card 300.

[0045] The examples have been described with a two-part source electrode. However, the source electrode could be one-part.

[0046] Furthermore, the invention has been described with a microwave module 200 comprising a microwave chip 210. But the microwave module 200 could comprise several of them, in particular connected to each other.

Claims

Claims

1. Microwave module (200, 400, 500, 600) comprising: • a microwave chip (210), comprising a substrate (213), an active layer (211) on a first face of the chip (210), an electrical ground layer (212) on a second face opposite the first face, the active layer (211) comprising microstrip guide transmission lines; • a housing (220) encapsulating the microwave chip (210), said housing (220) comprising a redistribution layer (224) covering the active layer (211) of the microwave chip (210) and comprising electrical connection traces (225, 226, 227) for a connection between the active layer (211) and an electrical interface (228, 229) of the microwave module;said active layer (211) comprising at least one transistor (214), one or more of the electrical traces of the redistribution layer (224), called ground traces (227, 427, 527', 527”, 627), connecting a source electrode of the transistor (214) to one or more of the electrical interfaces, called ground interfaces (229, 429', 429”, 529', 529”, 629), said one or more ground interfaces (229, 429', 429”, 529', 529”, 629) being configured to be connected to a ground (322) of an electronic card (300).;

2. Microwave module (200, 400, 500) according to the preceding claim, wherein the ground interface(s) (229, 429', 429”, 529', 529”) and the ground trace(s) (227, 427, 527', 527”) are arranged symmetrically with respect to said transistor (214).

3. A microwave module (200, 400, 500, 600) according to claim 1 or 2, wherein the source electrode comprises two portions (214', 214”, 414', 414”, 514', 514”, 614', 614”) located on either side of the transistor (214), said ground trace(s) (227, 427, 527', 527”, 627) connecting said portions to said ground interface(s) (229, 429', 429”, 529', 529”, 629).

4. A microwave module (200, 600) according to the preceding claim, wherein the source electrode is connected to a single ground interface (229, 629), the portions (214', 214”, 614', 614”) of the source electrode source being connected to said ground interface (229, 629).

5. Microwave module (200, 600) according to the preceding claim, wherein the parts (214', 214”, 614', 614”) of the source electrode are connected to said ground interface (229, 629) via a same ground trace (227, 427) or via respective ground traces.

6. A microwave module (400, 500) according to claim 3, wherein the source electrode is connected to a plurality of ground interfaces (429', 429”, 529', 529”), the portions (414', 414”, 514', 514”) of the source electrode being connected to said ground interfaces (429', 429”, 529', 529”).

7. A microwave module (500) according to the preceding claim, wherein each portion (514', 514”) of the source electrode is connected to a respective ground interface (529', 529”) via a respective ground trace (527', 527”).

8. A microwave module (400) according to claim 6, wherein the portions (414', 414”) of the source electrode are connected to the ground interfaces (429', 429”) via a same ground trace (427).

9. Microwave module (200, 400, 500, 600) according to one of the preceding claims, wherein the microwave chip (210) further comprises an electrical connection (217) between the source electrode of the transistor (214) and the electrical ground layer (212) of the chip, through the substrate (213) of the microwave chip (210).

10. Assembly comprising: • a microwave module (200, 400, 500, 600) according to one of the preceding claims, • an electronic card (300) comprising an electrical ground layer (322), said microwave module (200, 400, 500, 600) being mounted on the electronic card (300) so that the active layer (211) of the chip is oriented towards said electronic card (300), said ground interface(s) (229, 429', 429”, 529', 529”, 629) being electrically connected to the ground (322) of the electronic card (300).

11. Assembly according to the preceding claim, in which the microwave module (200, 400, 500, 600) is mounted on the electronic card (300), one face of the microwave module, comprising said ground interface(s) (229, 429', 429”, 529', 529”, 629), being in with respect to the electronic card (300), so that said ground interface(s) (229, 429', 429”, 529', 529”, 629) come against a terminal (325, 325', 325”) of the electronic card (300).

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