Method and system for manufacturing printed circuit board with embedded cooling cavity, and printed circuit board

Abstract

The present disclosure concerns a method for manufacturing a printed circuit board with an embedded cooling cavity. The method comprises: - machining a part of a soluble material to form a pattern; - plating the pattern; - filling the plated pattern with an electrically insulating material; and - removing a remaining soluble material with a solvent to form a cooling cavity.

Description

DESCRIPTIONTitle of InventionMETHOD AND SYSTEM FOR MANUFACTURING PRINTED CIRCUIT BOARD WITH EMBEDDED COOLING CAVITY, AND PRINTED CIRCUIT BOARDTechnical Field

[0001] The present disclosure relates to a method and a system for manufacturing a printed circuit board with an embedded cooling cavity, and a printed circuit board.Background Art

[0002] Printed circuit boards (PCB) embedding windings intrinsically demonstrate clear advantages such as low profile, ease of manufacturability, repeatability of electrical parameters and improved thermal performances.

[0003] They may be used in planar magnetics components, like for example transformers and inductors. Despite this, the planar magnetics components are systematically restricted to niche markets in the low to moderate power ranges. With the advent of Wide Band Gap devices (WBG) such as Silicon Carbide (SiC) or Gallium Nitride (GaN), the current power converters operate at much higher switching frequencies compared to their Silicon counterpart. The constraints on magnetics are consequently mitigated, opening for the PCB-based planar field to higher power levels.

[0004] Due to their systematic use in high density systems, effective thermal management is a challenging task. In high power applications, liquid cooling is mostly used. However, conventional cold plates can only cool down from external sides of the devices, i.e. the magnetic materials. This results in a poor heat extraction from the core of the system (i.e. copper windings) which becomes the limiting factor in the design. Indeed, further increase in the power density would imply to increase the current density, resulting in higher losses with limited cooling area. For mitigation purpose, it is conventionally recommended to connect the windings to the cold plate through copper blocks insulated with thermal interface materials.

[0005] An object of the present disclosure is to cool down PCB windings from the vicinity thereof to reduce hot spots as much as possible. On the other hand, the cooling system should be selected to avoid adding excessive losses that could emerge from locating a metallic part in the vicinity of an AC magnetic field (eddy currents). Finally, the electric insulation of the cooling device is a critical point for safety of persons. From a manufacturing point of view, the strength of PCB-based windings is the cost effectiveness and the high repeatability in dimensions.Citation ListPatent Literature

[0006] United States Patent No. 7289329Summary of Invention

[0007] The present disclosure aims to provide a method and a system which provide an efficient cooling system for windings intended to be used in magnetic components.

[0008] To that end, the present disclosure concerns a method for manufacturing a printed circuit board with an embedded cooling cavity, the method comprising:- machining a part of a soluble material to form a pattern;- plating the pattern;- filling the plated pattern with an electrically insulating material; and- removing a remaining soluble material with a solvent to form a cooling cavity.

[0009] The present disclosure also concerns a system for manufacturing a printed circuit board with an embedded cooling cavity , the system being configured to:- command machining a part of a soluble material to form a pattern;- command plating the pattern;- command filling the plated pattern with an electrically insulating material; and- command removing a remaining soluble material with a solvent to form a cooling cavity.

[0010] Thus, the plated pattern can be used as a heat management system with a fluid or gas flowing thereinside to cool down the printed circuit board. Since the cooling system is embedded into the PCB, the heat management is significantly improved due to a reduced number of thermal interfaces when compared toconventional techniques. The plated pattern can also be used to carry an electrical current. In such a case, the coolant has to be wisely chosen with regards to the dielectric properties since the potential of the pattern is applied to the coolant. Since the device is able to carry current, it can be advantageously used in a magnetic component such an inductor or a transformer.

[0011] According to a particular feature, the method further comprises, prior to removing the remaining soluble material with the solvent- machining another part of the soluble material to form another pattern;- plating the other pattern; and- filling the other plated pattern with an electrically conductive material.

[0012] Thus, electrical formed patterns filled with electrically conductive materials used for carrying current and cooling parts are no longer in contact. Since the insulation is ensured by the electrically insulating material between the patterns, no specific attention must be paid to the coolant with respect to its dielectric abilities or ionization risks. In case of using conductive fluids, the hydraulic circuit must not have to be electrically insulated. Current carrying capabilities remain possible.

[0013] According to a particular feature, the method further comprises:- laminating a substrate including at least the electrically insulating material; and- inserting the laminated substrate in a magnetic component.

[0014] Thus, the obtained circuit board can be used for only cooling purpose but also as a set of windings carrying current and consequently magnetizing the magnetic component.

[0015] According to a particular feature, the method further comprises, prior to inserting the laminated substrate in the magnetic component, performing at least one of chemical etching and drilling on a lamination to make an electrical connection.

[0016] According to a particular feature, an obtained printed circuit board is inserted between primary winding’s conductors and secondary winding’s conductors of a transformer.

[0017] Thus, the cooling system is located in the middle of the transformer and prevents hot spots normally located in this area.

[0018] According to a particular feature, two obtained printed circuit boards are located at a top of primary winding’s conductors and at a bottom of secondary winding’s conductors of a transformer.

[0019] Thus, the cooling system can both cool down the primary winding’s conductors with a core part on the top side and the secondary winding’s conductors with a core part on the bottom side. In addition to that, this arrangement helps reduce eddy losses into the obtained printed circuit board since located the near-zero field area.

[0020] According to a particular feature, two obtained printed circuit boards are stacked, each thereof being inserted in a magnetic component, one obtained printed circuit board acting as a primary winding of a transformer, and the other obtained printed circuit board acting as a secondary winding of the transformer.

[0021] Thus, the heat extraction is directly done inside the windings for optimal results.

[0022] The present disclosure also concerns a printed circuit board, comprising:- an embedded cooling cavity, at least part of the cooling cavity being surrounded by a plating.Brief Description of Drawings

[0023] The characteristics of the disclosure will emerge more clearly from a reading of the following description of example embodiments, the said description being produced with reference to the accompanying drawings, among which:Fig. 1a represents a first example of an algorithm for manufacturing a printed circuit board embedding a cooling cavity according to the present disclosure that may be used in a magnetic component;Fig. 1b represents a second example of an algorithm for manufacturing a printed circuit board embedding a cooling cavity according to the present disclosure that may be used in a magnetic component;Fig. 2 represents an example of an architecture of a device for manufacturing a printed circuit board embedding a cooling cavity according to the present disclosure that may be used in a magnetic component;Fig. 3 represents an example of a printed circuit board embedding a cooling cavity according to the present disclosure;Figs. 4a to 4h represent an example of different steps for manufacturing a printed circuit board embedding a cooling cavity according to the present disclosure;Figs. 5a to 5h represent an example of different steps for manufacturing a printed circuit board embedding a cooling cavity according to the present disclosure;Figs. 6a to 6f represent an example of different steps for manufacturing a printed circuit board embedding a cooling cavity according to the present disclosure;Fig. 7 represents an example of a magnetic component comprising a printed circuit board embedding a cooling cavity according to the present disclosure;Fig. 8 represents an example of a magnetic component comprising a printed circuit board embedding a cooling cavity according to the present disclosure; andFig. 9 represents an example of a magnetic component comprising a printed circuit board embedding a cooling cavity according to the present disclosure.Description of Embodiments

[0024] Fig. 1a represents a first example of an algorithm for manufacturing a printed circuit board embedding a cooling cavity according to the present disclosure that may be used in a magnetic component. As shown in Fig. 1a, the present algorithm includes steps S100 to S105.

[0025] The present algorithm is executed by a device 20 for manufacturing a printed circuit board embedding a cooling cavity according to the present disclosure that may be used in a magnetic component that will be disclosed hereinafter in reference to Fig. 2.

[0026] The device 20 may constitute a system for manufacturing a printed circuit board with an embedded cooling cavity.

[0027] The present disclosure uses subtractive manufacturing applied to PCB technology. To achieve this goal, a conventional prepreg material is locally replaced by a special soluble preg material with a liquid or solvent The conventional preg material is a material that is not soluble. In other words, the conventional non-soluble preg material is not soluble with a liquid or solvent that can dissolve the soluble preg material. The soluble preg material is, for example, Polyvinyl alcohol, Butenediol Vinyl Alcohol Co-polymer or inorganic salts in a compressed form. The solvent may be water.

[0028] PCB PP (Prepreg), or Pre-preg, is a shorthand expression for Pre- Impregnated, also referred to as Preg, which is composed of fiberglass fabric impregnated with resin. The resin has been partially cured but not hardened during the Prepreg coating operation. When heating the PCB during pressing process, the resin in Prepreg flows, sticks and bonds a PCB core with copper foil or other materials.

[0029] An example of a component embedding a cooling cavity is given in Fig. 4a.

[0030] In Fig. 4a, a substrate is composed of a soluble preg material 400 and two layers of copper 401 and 402.

[0031] Specifically, the soluble preg material 400 has, for example, a plate shape, and the two layers of copper 401 and 402 are provided on two sides of the soluble preg material 400. In other words, the layer of copper 401 , the soluble preg material 400, and the layer of copper 402 are arranged in a thickness direction of the soluble preg material 400. The thickness direction is equal to the up-down direction of Figs. 4a to 4h.

[0032] At step S100, the device 20 commands the realization of electric pattern of the magnetic component embedding a cooling cavity.

[0033] In other words, the device 20 commands machining a part of the soluble preg material 400 to form a pattern, or the device 20 may command a machining apparatus (for example, milling machine or drilling machine) to machine a part of the soluble preg material 400 to form a pattern. The system for manufacturing a printed circuit board with an embedded cooling cavity may include the machining apparatus.

[0034] The substrate is basically drilled or milled in order to form mechanical vias (i.e. , holes or slits) or microvias or patterns according to the thickness of the substrate.

[0035] An example is given in Fig. 4b.

[0036] In Fig. 4b, apertures 410a to 410g are realized in the substrate composed of the soluble preg material 400 and the two layers of copper 401 and 402.

[0037] The apertures 410a to 410g penetrate the substrate in the thickness direction.

[0038] The pattern is formed of the apertures 410a to 410g and the remaining soluble preg materials 400.

[0039] At step S101 , the device 20 commands the plating of the apertures 410a to 410g with for example copper.

[0040] In other words, the device 20 commands plating the pattern, or the device 20 may command a plating apparatus to plate the pattern. The plating apparatus may include, for example, a plating tank. The system for manufacturing a printed circuit board with an embedded cooling cavity may include the plating apparatus.

[0041] An example is given in Fig. 4c which shows the copper plating 420 of the apertures.

[0042] The plating 420 is formed on inner surfaces of the apertures. In other words, the plating 420 is formed on side surfaces of the remaining soluble preg material 400 that faces the apertures. At this time, a plating may be formed on the top surface of the layer of copper 401 and the lower surface of the layer of copper 402.

[0043] At step S102, the device 20 commands the filling of the apertures with an electrically insulating material like for example resin. The resin is for example TAIYO THP-100 DX1 proposed by the company TAIYO AMERICA™ or resin provided by the company Micromax™ CB100.

[0044] In other words, the device 20 commands filling the plated pattern with an electrically insulating material, or the device 20 may command a filling apparatus to fill the plated pattern with an electrically insulating material. The filling apparatus may be, for example, a coater, an injector, a dispenser or the like. The system formanufacturing a printed circuit board with an embedded cooling cavity may include the filling apparatus.

[0045] An example is given in Fig. 4d which shows the filings 430a to 430g of the apertures by resin.

[0046] The resin (i.e. , the electrically insulating material) is not soluble with a solvent that can dissolve the soluble preg material 400.

[0047] At step S103, the substrate obtained at step S102 is laminated in order to obtain a PCB as shown in Fig. 4e.

[0048] The substrate obtained at step S102 includes at least the filings 430a to 430g (i.e., the electrically insulating material).

[0049] The Fig. 4e shows the substrate obtained at step S102 on the top of which a layer of conventional prepreg material 441 and a copper layer 440 are laminated and on the bottom of which a layer of conventional prepreg material 442 and a copper layer 443 are laminated.

[0050] In other words, the copper layer 440, the prepreg material 441 , the substrate, the prepreg material 442, and the copper layer 443 are arranged in the thickness direction.

[0051] At step S104, the copper layers are respectively electrically connected by vias 450 and 451 shown in Fig. 4f to plating layers made at step S101 , and the copper layers are chemically etched or drilled in order to form an inductive component composed of the conducting patterns 460a to 460I as shown in Fig. 4g.

[0052] In other words, at least one of chemical etching and drilling is performed on a lamination (i.e., the copper layers 440 and 443 and the prepreg materials 441 and 442) to make an electrical connection through the vias 450 and 451 .

[0053] At step S105, the soluble prepreg is removed using a solvent.

[0054] In other words, the device 20 may command removing a remaining soluble preg material with a solvent to form a cooling cavity, or the device 20 may command a removing apparatus to remove a remaining soluble preg material with a solvent to form a cooling cavity. The removing apparatus may include, for example, an injector that can supply a solvent. The system for manufacturing aprinted circuit board with an embedded cooling cavity may include the removing apparatus.

[0055] As a result, plated apertures 470a to 470f shown in Fig. 4h and the conducting patterns 460a to 460I form an inductor.

[0056] The apertures 470a to 470f correspond to the cooling cavities. Part of each of the apertures 470a to 470f is surrounded by a plating made at step S101 .

[0057] That is, the printed circuit board includes the embedded cooling cavity, and at least part of the cooling cavity is surrounded by a plating.

[0058] Fig. 1b represents a second example of an algorithm for manufacturing a printed circuit board embedding a cooling cavity according to the present disclosure that may be used in a magnetic component. As shown in Fig. 1 b, the present algorithm includes steps S120 to S126.

[0059] The present algorithm is executed by a device 20 for manufacturing a printed circuit board embedding a cooling cavity according to the present disclosure that may be used in a magnetic component that will be disclosed hereinafter in reference to Fig. 2.

[0060] The device 20 of the present algorithm of the second example may perform similar functions to those of the above first example.

[0061] The present disclosure uses subtractive manufacturing applied to PCB technology. To achieve this goal, a conventional prepreg material is locally replaced by a special soluble preg material with a liquid or solvent.

[0062] Preferably, the soluble material is soluble into a cooling liquid material which will be used, at least partially, during cooling. For example, the cooling liquid material is water. For example, the soluble material is Polyvinyl alcohol (PVA) which can stand a lamination temperature. For example, the soluble material is Butenediol Vinyl Alcohol Co-polymer. For example, the soluble material is inorganic salts like for example NaCI in a compressed form.

[0063] PCB PP (Prepreg), or Pre-preg, is a shorthand expression for Pre- Impregnated, also referred to as Preg, which is composited of fiberglass fabric impregnated with resin. The resin has been partially cured but not hardened during the Prepreg coating operation. When heating the PCB during pressing process,the resin in Prepreg flows, sticks and bonds the PCB core with copper foil or other materials.

[0064] An example is given in Fig. 5a.

[0065] In Fig. 5a, a substrate is composed of a soluble preg material 500 and two layers of copper 501 and 502.

[0066] At step S120, the device 20 commands the realization of electric pattern of the magnetic component embedding a cooling cavity.

[0067] The substrate is basically drilled or milled with mechanical vias (i.e., holes or slits) or microvias or patterns according to the thickness of the substrate.

[0068] An example is given in Fig. 5b.

[0069] In Fig. 5b, apertures 510a to 51 Od are realized in the substrate composed of the soluble preg material 500 and the two layers of copper 501 and 502.

[0070] Another example is given in Fig. 6a.

[0071] In Fig. 6a, a conventional prepreg material 600 is locally replaced by a special soluble preg material 601.

[0072] The soluble preg material 601 is milled in order to form three cavities 602.

[0073] In other words, the soluble preg material 601 is milled to form a winding cavity 602.

[0074] The substrate is intended to be placed in a magnetic core 603.

[0075] At step S121 , the device 20 commands the plating of the apertures 510a to 51 Od or the milled pattern 602 with for example copper.

[0076] An example is given in Fig. 5c which shows copper plating 520 of the apertures.

[0077] At step S122, the device 20 commands the filling of the apertures with an electrically conductive material like for example copper. An example is given in Fig. 5d which shows fillings 530a to 530c of the apertures by copper.

[0078] Another example is given in Fig. 6b which shows a filling 612 that is copper plated and filled by copper.

[0079] The fillings of copper may be filled by using a plating apparatus, a coater, an injector, a dispenser or the like.

[0080] A step S123, the device 20 commands performing at least one of the drilling and milling of the substrate.

[0081] The substrate is basically drilled or milled with mechanical vias (i.e. , holes or slits) or microvias or patterns according to the thickness of the substrate.

[0082] An example is given in Fig. 5e.

[0083] In Fig. 5e, apertures 540a to 540c are realized in the substrate composed of the soluble preg material 500 and the two layers of copper 501 and 502.

[0084] Another example is given in Fig. 6c wherein the soluble preg material is milled in order to form cavities 630 separating the filed windings (i.e., the filling 612, refer to Fig. 6b).

[0085] At the same step, the cavities 630 are electroless plated in order to form electroless plated cavities 640 as shown in Fig. 6d.

[0086] At step S125, the device 20 commands the filling of the apertures made at step S123 with an electrically insulating material like for example resin. An example is given in Fig. 5f which shows fillings 550a to 550c of the apertures by resin.

[0087] Another example is given in Fig. 6e which shows a filling 651 of the apertures by resin.

[0088] At step S126, the soluble prepreg is removed using solvent.

[0089] An example is given in Fig. 6f.

[0090] As a result, the plated apertures, the plated via and the vias filled by copper form a conducting pattern that comprises a cooling channel made by the cavities revealed by the removed soluble prepreg and the cooling channel acts also as conducting patterns.

[0091] According to a particular feature, the following steps are performed:- laminating the obtained substrate in order to obtain a PCB as shown in Fig. 5g,- electrically connecting copper layers respectively by vias 570 and 571 toplating layers formed at step 121 shown in Fig. 5h and chemically etching or drilling the copper layers in order to form an inductive component composed of the conducting patterns.

[0092] The Fig.5g shows the PCB obtained at step S126 on the top of which a layer of conventional prepreg material 561 and a copper layer 560 are laminated and on the bottom of which a layer of conventional prepreg material 562 and a copper layer 563 are laminated.

[0093] Fig. 2 represents an example of an architecture of a device for manufacturing a printed circuit board embedding a cooling cavity according to the present disclosure that may be used in a magnetic component.

[0094] The device 20 for manufacturing a printed circuit board embedding a cooling cavity according to the present disclosure that may be used in a magnetic component has, for example, an architecture based on components connected together by a bus 201 and a processor 200 controlled by a program as disclosed in Fig. 1a or 1 b.

[0095] The bus 201 links the processor 200 to a read only memory (ROM) 242, a random access memory (RAM) 203 and an input output interface (I / O l / F) 205.

[0096] The memory 203 contains registers intended to receive variables and the instructions of the program related to the algorithm as disclosed in Fig. 1a or 1 b.

[0097] The read only memory, or possibly a Flash memory 242, contains instructions of the programs related to the algorithm as disclosed in Fig. 1a or 1 b, when the device 20 is powered on, are loaded to the random access memory 203. Alternatively, the program may also be executed directly from the ROM 242.

[0098] The control performed by the device 20 may be implemented in software by execution of a set of instructions or program by a programmable computing machine, such as a PC (Personal Computer), a DSP (Digital Signal Processor) or a microcontroller; or else implemented in hardware by a machine or a dedicated component, such as an FPGA (Field-Programmable Gate Array) or an ASIC (Application-Specific Integrated Circuit).

[0099] In other words, the device 20 includes circuitry, or a device including circuitry, causing the device 20 to perform the program related to the algorithm as disclosed in Fig. 1a or 1 b.

[0100] Further in other words, the device 20 may include at least a memory (for example, the RAM 203) in which a program is loaded, and the processor 200 that can execute the program to perform the above functions.

[0101] Fig. 3 represents an example of a printed circuit board embedding a cooling cavity according to the present disclosure.

[0102] In the example of Fig. 3, a conventional prepreg material 31 is locally replaced by a soluble preg material 32. The conventional prepreg material and the soluble prepreg material are milled in order to provide a channel 33 that is plated with a conductive material like copper in order to provide an electrically conducting pattern. After dissolution of the soluble prepreg, a liquid or a gas is injected in the channel formed by the dissolved soluble prepreg in order to provide a cooling cavity.

[0103] Fig. 7 represents an example of a magnetic component comprising a printed circuit board embedding a cooling cavity according to the present disclosure.

[0104] In the example of Fig. 7, a printed circuit board embedding a cooling cavity 701 is solely used as a cooler located at the closest of primary winding’s conductors 700 and secondary winding’s conductors 702 and more precisely between the primary and the secondary windings. The cooling cavities are not carrying any of the magnetic device current. However, since the cooling cavities are fully or partially made of a conductive material, eddy currents are generated in the cooling cavities due to the presence of the near magnetic field generated by the magnetic device. The density of vias can also be adjusted to control the pressure drop of a pumping device and customize the effective cooling.

[0105] Since the printed circuit board embedding a cooling cavity 701 is used as a cooler, the copper layers 440 and 443 and the prepreg materials 441 and 442 shown in Fig. 4e or the copper layers 560 and 563 and the prepreg materials 561 and 562 shown in Fig. 5g may not be provided therein.

[0106] Fig. 8 represents an example of a magnetic component comprising a printed circuit board embedding a cooling cavity according to the present disclosure.

[0107] In the example of Fig. 8, printed circuit boards embedding cooling cavities 800 and 803 are solely used as a cooler located at the closest of primary winding’s conductors 801 and secondary winding’s conductors 802 and more precisely at the top of the primary windings 801 and at the bottom of the secondary windings 803. The cooling cavities are not carrying any of the magnetic device current. However, since the cooling cavities are fully or partially made of a conductive material, eddy currents are generated in the cooling cavities due to the presence of the near magnetic field generated by the magnetic device. The density of vias can be also adjusted to control the pressure drop of a pumping device and customize the effective cooling.

[0108] Since the printed circuit boards embedding cooling cavities 800 and 803 are used as coolers, the copper layers 440 and 443 and the prepreg materials 441 and 442 shown in Fig. 4e or the copper layers 560 and 563 and the prepreg materials 561 and 562 shown in Fig. 5g may not be provided therein.

[0109] Fig. 9 represents an example of a magnetic component comprising a printed circuit board embedding a cooling cavity according to the present disclosure.

[0110] In the example of Fig. 9, printed circuit boards embedding cooling cavities 900 and 901 respectively are used as primary and secondary windings.

[0111] Naturally, many modifications can be made to the embodiments of the disclosure described above within the scope of the present disclosure.

[0112] In the above embodiments, the soluble preg materials 400, 500 and 601 are used, but the present disclosure is not limited to this. A soluble material such as Polyvinyl alcohol (PVA), Butenediol Vinyl Alcohol Co-polymer, or inorganic salts like for example NaCI in a compressed form may be used instead of the soluble preg material 400, 500 or 601 . The soluble material may include no fiberglass fabric.

Claims

CLAIMS

1. A method for manufacturing a printed circuit board with an embedded cooling cavity, the method comprising:- machining a part of a soluble material to form a pattern;- plating the pattern;- filling the plated pattern with an electrically insulating material; and- removing a remaining soluble material with a solvent to form a cooling cavity.

2. The method according to claim 1 , wherein the method further comprises, prior to removing the remaining soluble material with the solvent:- machining another part of the soluble material to form another pattern;- plating the other pattern; and- filling the other plated pattern with an electrically conductive material.

3. The method according to claim 1 or 2, wherein the method further comprises:- laminating a substrate including at least the electrically insulating material; and- inserting the laminated substrate in a magnetic component.

4. The method according to claim 3, wherein the method further comprises, prior to inserting the laminated substrate in the magnetic component, performing at least one of chemical etching and drilling on a lamination to make an electrical connection.

5. The method according to any one of claims 1 to 4, wherein an obtained printed circuit board is inserted between primary winding’s conductors and secondary winding’s conductors of a transformer.

6. The method according to any one of claims 1 to 4, wherein two obtained printed circuit boards are located at a top of primary winding’s conductors and at a bottom of secondary winding’s conductors of a transformer.

7. The method according to any one of claims 1 to 4, wherein two obtained printed circuit boards are stacked, each thereof being inserted in a magnetic component, one obtained printed circuit board acting as a primary winding of a transformer, and the other obtained printed circuit board acting as a secondary winding of the transformer.

8. A system for manufacturing a printed circuit board with an embedded cooling cavity, the system being configured to:- command machining a part of a soluble material to form a pattern;- command plating the pattern; - command filling the plated pattern with an electrically insulating material; and- command removing a remaining soluble material with a solvent to form a cooling cavity.

9. A printed circuit board, comprising:- an embedded cooling cavity, at least part of the cooling cavity being surrounded by a plating.

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