Method and device for making integrated cooling liquid chambers in printed circuit boards

Abstract

The invention relates to a method and apparatus for making an integrated cooling fluid cavity in a printed circuit board by inserting a power semiconductor die into a dielectric material; laminating the dielectric material with a dielectric material and a thin conductive layer on each side of the dielectric material; drilling a via through the laminated copper and dielectric layers; metallizing the via to form a first printed circuit board; laminating a dielectric material, a soluble material having a predetermined form, and a conductive layer on the first printed circuit board; injecting a solvent into the soluble material to dissolve the soluble material and reveal a cavity; injecting a cooling fluid into the revealed cavity.

Description

Technical Field

[0001] This invention generally relates to an integrated coolant cavity in a printed circuit board and a method for manufacturing the same. Background Technology

[0002] A general trend in power electronics is to increase the power density of converters. This trend is driven by specific application requirements. For example, in electric vehicle applications, increased power density allows for more space to be allocated to the passenger compartment, and in the case of hybrid electric vehicles (HEVs), weight savings contribute to extended range or reduced CO2 emissions. In consumer electronics applications, more compact power converters are key to miniaturization, as clearly seen in smartphone or laptop chargers.

[0003] The increasing switching frequency and power density have led to an urgent need for thermal enhancement in the packaging of power electronic products.

[0004] An emerging solution in power packaging is to embed the die into the substrate (mainly printed circuit board (PCB)) and connect the power die via vias.

[0005] With the advent of wide-bandgap semiconductors such as silicon carbide (SiC) and gallium nitride (GaN), the combination of smaller die area, higher operating temperature, and compact packaging required for high-frequency operation is shrinking the available surface area for heat extraction. In this context, it is necessary to optimize every part of the heat path. Besides the thermal interface material layer, in the context of embedded die packaging, the layer made of filled copper vias and the remaining dielectric material is a bottleneck in this thermal path. The pursuit of higher power density in converters leads to an increase in heat flux density near the die. The limited density of the aforementioned copper microvias currently hinders the heat transfer capabilities of high-power embedded die power packages. Summary of the Invention

[0006] The purpose of this invention is to provide an integrated coolant cavity in a printed circuit board and a method for manufacturing the same.

[0007] Therefore, the present invention relates to a method for fabricating an integrated coolant cavity in a printed circuit board, characterized in that the method includes the following steps:

[0008] Insert the power semiconductor die into the dielectric material;

[0009] The dielectric material is laminated with a dielectric material and a thin conductive layer on each side of the dielectric material;

[0010] Drill through the laminated copper and dielectric layers to create vias;

[0011] The vias are metallized to form a first printed circuit board;

[0012] On the first printed circuit board, dielectric material, soluble material having a predetermined form, and conductive layer are laminated in the same plane;

[0013] The solvent is injected into the soluble material to dissolve the soluble material and expose the cavity;

[0014] Inject coolant into the exposed cavity.

[0015] The present invention also relates to an apparatus for fabricating an integrated coolant cavity in a printed circuit board, characterized in that the apparatus comprises:

[0016] A device for inserting a power semiconductor die into a dielectric material;

[0017] A means for laminating the dielectric material with a dielectric material and a thin conductive layer on each side of the dielectric material;

[0018] Device for drilling through laminated copper and dielectric layers to create vias;

[0019] Apparatus for metallizing the vias to form a first printed circuit board;

[0020] A means for laminating dielectric material, a soluble material having a predetermined form, and a conductive layer on the same plane on the first printed circuit board;

[0021] Apparatus for injecting solvent into the soluble material to dissolve the soluble material and expose a cavity;

[0022] A device for injecting coolant into an exposed cavity.

[0023] Therefore, the coolant comes into direct contact with the nearest conductive layer, which greatly reduces the thermal path between the die and the coolant.

[0024] Depending on the specific features, the method includes the step of drilling blind vias through the conductive layer before injecting the solvent.

[0025] Depending on the specific characteristics, the method may also include the step of coating / plating blind vias.

[0026] Therefore, electrical continuity is provided between the conductive layers, and the conductive layer above the cavity to be exposed will be supported by these vias.

[0027] Depending on the specific features, the method includes the step of coating / plating the exposed cavity before injecting coolant.

[0028] Therefore, it is possible to create cavities inside a printed circuit board using a soluble portion. In effect, this portion maintains pressure during all lamination steps and prevents uncured dielectric material from flowing into the cavity later. Because this portion is trapped within the printed circuit board structure, only soluble materials can be used.

[0029] Depending on their specific characteristics, soluble materials are polyvinyl alcohol, butanediol-vinyl alcohol copolymers, or inorganic salts in compressed form.

[0030] The features of the invention will become more apparent from the following description of exemplary embodiments, with reference to the accompanying drawings. Attached Figure Description

[0031] Figure 1a This refers to a power semiconductor inserted into a dielectric material.

[0032] Figure 1b This is an enlarged cross-sectional view of a die inserted into a dielectric material.

[0033] Figure 2 This refers to a printed circuit board with layers of dielectric and conductive materials laminated on each side.

[0034] Figure 3 This refers to the printed circuit board after laser drilling of vias.

[0035] Figure 4 This indicates the etching of the conductive material on a printed circuit board.

[0036] Figure 5 This refers to a printed circuit board 50 after a dielectric material is laminated together with a specific type of mold made of a soluble material and a thick conductive layer.

[0037] Figure 6 This refers to the printed circuit board after blind vias have been mechanically drilled.

[0038] Figure 7 This refers to the printed circuit board after the holes used to cool the power semiconductors have been drilled.

[0039] Figure 8 This is a cross-sectional view of the printed circuit board after the integrated coolant chamber is implemented.

[0040] Figure 9 This illustrates the architecture of an apparatus for implementing an integrated coolant cavity in a printed circuit board according to the present invention.

[0041] Figure 10 This illustrates an embodiment of the algorithm according to the present invention for implementing an integrated coolant cavity in a printed circuit board. Detailed Implementation

[0042] Figure 1a This refers to a power semiconductor inserted into a dielectric material.

[0043] In the embodiment of FIG1, the dielectric material 11 has a first cavity and a second cavity, into which corresponding power semiconductor dies Di1 and Di2 are inserted.

[0044] The thickness of the core is close to that of a die to be inserted. The electrode 12 of the die is shown in Figure 1.

[0045] Figure 1b This is an enlarged cross-sectional view of the die Di1 inserted into the dielectric material 11.

[0046] Figure 2 The dielectric material 11 refers to the dielectric material 11 after dielectric material 21 and thin conductive material 22 (e.g., copper layer) are laminated on each side of dielectric material 11 to obtain printed circuit board 20.

[0047] During lamination, dielectric material 21 flows into the space left in the cavity, thus “capturing” die Di1 into the printed circuit board 20.

[0048] At this stage, the top and bottom electrodes of the die are not connected to the conductive material.

[0049] Figure 3 This refers to the printed circuit board 30 after laser drilling of vias on the printed circuit board 20.

[0050] After vias are drilled through both the conductive material and the dielectric layer using micron-scale lasers, the metallization of the vias uses a sequence of processes, such as copper electroless plating and electroplating, to provide electrical continuity.

[0051] Figure 4 This indicates the etching of the conductive material on a printed circuit board.

[0052] This step creates the desired circuitry that connects the power die electrodes to external components.

[0053] For clarity, Figure 4 Only the gate connector 40 of the die is shown.

[0054] Figure 5 This refers to a printed circuit board 50 after a dielectric material is laminated together with a specific type of mold made of a soluble material and a thick conductive layer.

[0055] On top of the conductive layer 22, a dielectric material 52 is laminated together with a mold 53 of a specific form made of a soluble material. Simultaneously, a thick conductive layer 51 is laminated on top of the dielectric material. Figure 5In this embodiment, the soluble material is T-shaped. The portion made of the soluble material has a semi-tubular shape 55 extending throughout the entire portion and has at least one outlet pointing towards the edge of the final device. This particular shape is designed to allow minimal liquid flow to initiate the dissolution step. Other shapes may be used for the cavity, as long as they allow liquid flow and maintain lamination pressure.

[0056] Preferably, the soluble material is soluble in the coolant material that will be at least partially used during cooling. For example, the coolant material is water. For example, the soluble material is polyvinyl alcohol (PVA) that can withstand lamination temperatures. For example, the soluble material is a butanediol-vinyl alcohol copolymer. For example, the soluble material is a compressed form of an inorganic salt, such as NaCl.

[0057] Figure 6 This represents a printed circuit board after blind vias have been mechanically drilled. Blind vias 60 are mechanically drilled through the thick copper layer 51 down to the thin conductive layer 22. These vias serve two purposes. The first is to provide electrical continuity between the outer and inner conductive layers. The second is to act as pillars for the exposed cavity. These pillars will hold the thick conductive layer bridging the cavity above. Vias 60 are called structural vias. Structural vias are, for example, copper-plated. The goal of plating vias 60 is to create a barrier against coolant, and only a plating thickness of a few tens of micrometers is required. If additional strength is needed, vias 60 can be filled with polymer resin.

[0058] Figure 7 This refers to the printed circuit board after the holes used to cool the power semiconductors have been drilled.

[0059] The orifice 70 for cooling is machined using a standard milling / drilling system. Depending on the application, the orifice can be a hole or a more complex cavity. The depth of the orifice is slightly less than the sum of the thickness of the conductive layer and the soluble material. The orifice 70 is located on top of the soluble material and will expose the semi-tubular shape 55 within the soluble material.

[0060] Figure 8 This is a cross-sectional view of the printed circuit board after the integrated coolant chamber is implemented.

[0061] Grooves are cut into each side of the printed circuit board to allow liquid flow. Nozzles 85 are placed at the inlets of some or all of the orifices. The solvent flows through the orifices and continues through the cavity, finally exiting through the side of the printed circuit board. During injection, the material dissolves, and the internal structure gradually emerges beneath the thick conductive layer. The injection step ends when all soluble material has been completely removed.

[0062] At this stage, the column surfaces, base plate, and top plate of the internal structure 80 are made of conductive material, while the other walls are made of dielectric material (prepreg). Typically, dielectric materials used in printed circuit board manufacturing are hydrophilic and tend to swell after absorbing water-based liquids. Electroless deposition and electrodeposition are performed to create the coolant-sealed cavity. As for the structural vias 60, the required plating thickness depends on the need for a coating that protects the dielectric material from the coolant.

[0063] Figure 9 This illustrates the architecture of an apparatus according to the invention for implementing an integrated coolant cavity in a printed circuit board having an integrated coolant cavity.

[0064] A device for implementing an integrated coolant chamber in a printed circuit board 80, for example, has components connected together by a bus 901 and, as... Figure 10 The architecture of the program-controlled processor 900 disclosed in the paper.

[0065] Bus 901 links processor 900 to read-only memory ROM 902, random access memory RAM 903, and input / output (I / O) interface 905.

[0066] Memory 903 includes components designed to receive and Figure 10 The program's variables and instruction registers related to the publicly disclosed algorithm.

[0067] Read-only memory or possibly flash memory 902 contains with Figure 10 The instructions of the algorithm-related program disclosed herein are loaded into the random access memory 903 when the device used to implement the integrated coolant cavity in the printed circuit board 80 is powered on. Alternatively, the program can also be executed directly from the ROM memory 902.

[0068] Control by the means for implementing an integrated coolant chamber in the printed circuit board 80 can be implemented in software by a programmable computing machine such as a PC (personal computer), DSP (digital signal processor), or microcontroller executing a set of instructions or programs; or in hardware by a machine or special component such as an FPGA (field-programmable gate array) or ASIC (application-specific integrated circuit).

[0069] In other words, the means for implementing an integrated coolant cavity in the printed circuit board 80 includes a circuit or means including a circuit, such that the means for implementing an integrated coolant cavity in the printed circuit board 80 performs with Figure 10 The publicly available algorithm-related programs.

[0070] Figure 10 This illustrates an embodiment of the algorithm according to the present invention for implementing an integrated coolant cavity in a printed circuit board.

[0071] In step S1000, the power semiconductor is inserted into the dielectric material.

[0072] In the embodiment of FIG1, the dielectric material 11 has a first cavity and a second cavity, into which corresponding power semiconductor dies Di1 and Di2 are inserted.

[0073] The thickness of the core is close to that of a die to be inserted.

[0074] In step S1001, dielectric material 11 is laminated with dielectric material 21 and conductive material layer 22 on each side of dielectric material 11.

[0075] During lamination, dielectric material 21 flows into the space left in the cavity, thus “capturing” die Di1 into the printed circuit board 20.

[0076] In step S1002, a via is drilled through both the conductive material and the dielectric layer using a micrometer-scale laser, and the via is metallized using, for example, a sequence made of electroless and electroplated materials.

[0077] In step S1003, the desired circuit for connecting the power die electrode to an external component is created.

[0078] For clarity, Figure 4 Only the gate connector 40 of the die is shown.

[0079] In step S1004, dielectric material is laminated together with a specific form of mold and a thick conductive layer made of soluble material on the printed circuit board.

[0080] On top of the conductive layer 22, a dielectric material 52 is laminated together with a mold 53 of a specific form made of a soluble material. Simultaneously, a thick conductive layer 51 is laminated on top of the dielectric material.

[0081] The portion made of a soluble material has a semi-tubular shape 55 pointing towards its sides. This particular shape is designed to allow minimal liquid flow to initiate the dissolution step. Other shapes may be used for the cavity, as long as they allow liquid flow and maintain lamination pressure.

[0082] Preferably, the soluble material is soluble in the coolant material that will be at least partially used during cooling. For example, the coolant material is water. For example, the soluble material is polyvinyl alcohol (PVA) that can withstand lamination temperatures. For example, the soluble material is a butanediol-vinyl alcohol copolymer. For example, the soluble material is a compressed form of an inorganic salt, such as NaCl.

[0083] At step 1005, a blind via 60 is mechanically drilled through the thick copper layer 51 down to the thin conductive layer 22. The via 60 serves two purposes. First, it electrically connects the outer conductive layer to the inner conductive layer. Second, it acts as pillars for the exposed cavity. These pillars will hold the thick conductive layer bridging the cavity. The via 60 is called a structural via. Structural vias are, for example, plated with copper. The goal of plated via 60 is to create a barrier against the coolant, requiring only a thickness of a few tens of micrometers. If additional strength is needed, the via 60 can be filled with a polymer resin.

[0084] In step 1006, the conductive layer is etched to provide electrical connection.

[0085] In step 1007, an aperture for cooling the power semiconductor is drilled.

[0086] The orifice 70 for cooling is machined using a standard milling / drilling system. Depending on the application, the orifice can be a hole or a more complex cavity. The depth of the orifice is slightly less than the sum of the thickness of the conductive layer and the soluble material. The orifice 70 is located on top of the soluble material and will expose the semi-tubular shape 55 within the soluble material.

[0087] In step S1008, grooves are cut out on each side of the printed circuit board to allow liquid flow.

[0088] In step S1010, nozzle 85 is placed at the inlet of some or all of the orifices. Solvent flows through the orifices and continues through the cavity, finally exiting through the side of the printed circuit board. During solvent injection, the material dissolves, and the internal structure is exposed beneath the thick conductive layer. Injection ends when all soluble material has been completely removed.

[0089] At this stage, the column surfaces, base plate, and top plate of the internal structure 80 are made of conductive material, while the other walls are made of dielectric material (prepreg). Typically, dielectric materials used in printed circuit board manufacturing are hydrophilic and tend to swell after absorbing water-based liquids. Electroless and electrodeposition of the conductive material are performed to create a coolant-sealed cavity. As for the structural vias 60, the required plating thickness depends on the need for a coating that protects the dielectric material from the coolant.

[0090] Of course, many modifications can be made to the embodiments of the present invention described above without departing from the scope of the present invention.

Claims

1. A method for fabricating an integrated coolant cavity in a printed circuit board, characterized in that, The method includes the following steps: Insert the power semiconductor die into the dielectric material; The dielectric material is laminated with a dielectric material and a thin conductive layer on each side of the dielectric material; Drill through the laminated copper and dielectric layers to create vias; The vias are metallized to form a first printed circuit board; A dielectric material, a soluble material having a predetermined form, and a conductive layer are laminated on the first printed circuit board; Drill a blind via through the conductive layer; Coating / plating the blind vias; The blind via is filled with polymer resin; The solvent is injected into the soluble material to dissolve the soluble material and expose the cavity; Inject coolant into the exposed cavity.

2. The method according to claim 1, characterized in that, The method includes the step of coating / plating the exposed cavity before injecting the coolant.

3. The method according to any one of claims 1 to 2, characterized in that, The soluble material is polyvinyl alcohol, butanediol-vinyl alcohol copolymer, or an inorganic salt in compressed form.

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