CN117581317A

CN117581317A - Multilayer printed circuit board for planar transformer

Info

Publication number: CN117581317A
Application number: CN202280045860.XA
Authority: CN
Inventors: 丹尼尔·高纳; 拉塞·彼得里·帕尔姆; 皮尼万·蒂万卡·班达拉·维耶孔
Original assignee: Huawei Digital Power Technologies Co Ltd
Current assignee: Huawei Digital Power Technologies Co Ltd
Priority date: 2022-01-07
Filing date: 2022-01-07
Publication date: 2024-02-20
Also published as: WO2023131417A1; EP4441763A1

Abstract

A multi-layer printed circuit board (printed circuit board, PCB) (100) for a planar transformer, comprising: a bottom surface (101); a top surface (102); at least one side (103); at least one first metal layer (110) operating in a first voltage range and embedded in the multilayer PCB above the bottom surface; at least one second metal layer (120) operating in a second voltage range and embedded over the at least one first metal layer in the multi-layer PCB; at least one planar insulating layer (130) and/or at least one lateral insulating layer (140). The planar insulating layer (130) is embedded in the multi-layer PCB (100) and serves to electrically isolate and electrically insulate the first metal layer (110) from the second metal layer (120). The lateral insulating layer (140) is embedded in the multilayer PCB and serves to electrically isolate and electrically insulate the second metal layer (120) from the lateral environment (106).

Description

Multilayer printed circuit board for planar transformer

Technical Field

The present invention relates to planar transformers in the field of power electronics and in power electronics applications. The invention relates in particular to a multilayer printed circuit board (printed circuit board, PCB) for a planar transformer, a planar transformer comprising such a multilayer PCB and a method of manufacturing such a multilayer PCB. More particularly, the present invention relates to an apparatus and method for embedded insulation of a high voltage PCB.

Background

Planar transformers are used for low power/low voltage applications. However, their use in the high-voltage (HV) and/or high-power (HP) fields has increased year by year. Examples of such applications are as follows: high voltage generators (capacitor charge, pulse generator, etc.); an isolated gate drive power supply for the medium voltage converter; a power supply, such as a solar rooftop DC-DC converter, connects the high voltage circuit and the Low Voltage (LV) circuit.

The applicability of planar transformers is limited by, among other reasons, insulation requirements. To ensure safety, planar transformers used in the above applications need to withstand high voltages during normal operation and commissioning (insulation withstand voltage test and pulse test). Typical voltage insulation requirements are specified in the standard IEC 62477-1. A system operating at 1kVdc should withstand a pulse voltage between 4kV and 12 kV. These voltages in turn define the minimum gap and creepage distance levels specified in the standard. The gap and creepage distance can be up to several millimeters. This makes the design of compact/miniature planar transformers challenging. This problem is exacerbated when the application is critical and supplemental (reinforcing) insulation is required, which may double the necessary gap/creepage distance.

Disclosure of Invention

The present disclosure provides an efficient and cost-effective solution for compact planar transformers, and a method of manufacturing such planar transformers that can withstand high voltages and can be used for the above applications.

The above and other objects are achieved by the features of the independent claims. Other implementations are apparent in the dependent claims, the description and the drawings.

The present invention solves the above-described basic problems. The present invention provides a concept for a single PCB structure with embedded HV planes and/or lateral isolation. While planar HV insulation reduces the distance between the HV and LV traces, lateral insulation may be required to reduce the gap and creepage distance from the HV winding to the transformer body (core). Lateral insulation can also be extended to applications without a magnetic core. In general, this may help reduce creepage distance and clearance requirements of the HV-PCB.

The basic idea presented in the present invention is to embed the concept of lateral insulation in a PCB with HV and LV traces. The HV trace is completely enclosed when combined with planar insulation. This solution enables a single PCB structure, ensuring repeatability and easier interconnection between HV and LV PCBs (signals). The gap and creepage distance may be significantly reduced, which may result in a wider AC trace, higher power density, and higher efficiency of the transformer.

However, even if only planar insulation (i.e. no lateral insulation) as described below is used, a single PCB structure may be provided, ensuring the above-mentioned advantages, i.e. repeatability and easier interconnection between HV and LV PCBs (signals). Even the gap and creepage distance can be significantly reduced using only planar insulation as described below, which results in a wider AC trace, higher power density, and higher efficiency of the transformer.

The solution disclosed below provides a single PCB structure as opposed to a conventional double PCB structure in which two separate PCBs are required, including sufficient space therebetween to meet the requirements regarding clearance and creepage distance.

With the disclosed single PCB structure, the following benefits may be realized: repeatability, easier interconnection between HV and LV traces, and thinner insulation, so normal low cost PCB processes can be used.

Embedded lateral and planar insulation may achieve the following: reducing the gap/creepage distance, which facilitates a compact design and higher power density; widening the HV trace reduces the AC resistance, thereby increasing power density and efficiency.

These benefits can be achieved even if only embedded planar insulation is used.

For the purposes of describing the present invention in detail, the following terms, abbreviations and symbols will be used:

PCB printed circuit board

HV high voltage, for example, 100kV and above in the present invention

MV medium voltage, for example, between 1500V and 100kV in the present invention

LV low pressure, e.g. below 1500V in the present invention

DC direct current

AC

In the present invention, a planar transformer is described. Planar transformers are high frequency transformers for high frequency operating, isolated switch mode power supplies. Planar transformers typically contain winding turns made of thin copper sheets that are riveted together at the ends of the turns in the case of high current windings or windings etched in spiral form on a PCB. Since the current conductor is a thin copper sheet, the operating frequency is not limited by skin effect. Thus, a high power converter constructed with planar transformers can be designed to operate at relatively high switching frequencies (typically 100kHz or higher). This may reduce the size of the magnetic elements and capacitors required, thereby increasing power density.

Planar transformers are becoming the mainstream of the power electronics field. The main advantages of the planar transformer are as follows: low profile: similar to other power electronics components, resulting in a more compact system. Low AC resistance: the PCB trace may reduce the AC resistance of the winding at higher frequencies, thereby increasing power density. Excellent heat dissipation capability: a larger surface area to volume ratio may increase the heat dissipation capacity. Repeatability: parasitic elements (leakage inductance and stray capacitance) are easier to control. This is an ideal choice for mass production.

According to a first aspect, the invention relates to a multilayer printed circuit board for a planar transformer, comprising: a bottom surface; a top surface opposite the bottom surface; at least one side; at least one first metal layer embedded above the bottom surface in the multilayer printed circuit board, the at least one first metal layer for conducting current, wherein the at least one first metal layer is for operating in a first voltage range; at least one second metal layer embedded over the at least one first metal layer in the multilayer printed circuit board, the at least one second metal layer for conducting electrical current, wherein the at least one second metal layer is for operating within a second voltage range, the second voltage range being at least partially different from the first voltage range; at least one planar insulating layer and/or at least one lateral insulating layer; wherein the at least one planar insulating layer is embedded between the at least one first metal layer and the at least one second metal layer in the multilayer printed circuit board, the at least one planar insulating layer being for electrically isolating and insulating the at least one first metal layer from the at least one second metal layer; wherein the at least one lateral insulating layer is embedded between the at least one second metal layer in the multilayer printed circuit board and the at least one side of the multilayer printed circuit board, the at least one lateral insulating layer being for electrically isolating and insulating the at least one second metal layer from a lateral environment of the at least one second metal layer.

The multilayer printed circuit board may also be part of a large PCB board that also has other features and parts.

It should be noted that the insulating layer actually separates the top and bottom sides of the PCB board from each other (electrically isolating and separating the top and bottom). All PCB layers are isolated, but additional layers enhance isolation.

Such multilayer printed circuit boards may be used as or within planar transformers. The multilayer printed circuit board is characterized by high power density, significantly reduced height (i.e., low profile), greater surface area (thereby improving heat dissipation capability), greater magnetic cross-sectional area (thereby reducing the number of turns), smaller winding area, winding structure that facilitates interleaving, lower leakage inductance (due to reduced number of turns and interleaving of windings), smaller AC winding resistance, and excellent reproducibility (achieved by winding structure). The winding structure may be realized by the at least one first metal layer and/or the at least one second metal layer.

The multilayer printed circuit board can meet the requirements of pulse withstand voltage and temporary overvoltage on system voltage, creepage distance requirements of functional insulation, basic insulation or auxiliary insulation and clearance distance requirements of functional insulation, basic insulation or auxiliary insulation according to standard IEC 60664-1 of different working voltages.

In one exemplary implementation of the multilayer printed circuit board, the lateral insulating layer extends at least in a portion transverse to the at least one second metal layer.

The vertical insulating layers (i.e., the lateral insulating layers) may extend to different lengths without extending to the planar insulating layers. The vertical insulating layer may pass through the entire PCB or may pass through only a portion of the entire PCB.

This has the following advantages: i.e. a flexible design according to creepage distance and clearance distance requirements (e.g. according to the standard IEC 60664-1 for different operating voltages) is achieved.

In one exemplary implementation of the multilayer printed circuit board, the multilayer printed circuit board includes: a top insulating layer formed at the top surface of the multilayer printed circuit board; wherein the at least one second metal layer is at least partially surrounded by insulating material of the top insulating layer, the planar insulating layer and the lateral insulating layer.

This has the following advantages: i.e. to substantially isolate the second metal layer, e.g. the high voltage part of the multi-layer PCB. Therefore, the structure can efficiently meet the requirements of creepage distance and clearance distance.

In one exemplary implementation of the multilayer printed circuit board, the multilayer printed circuit board includes: a laminate comprising at least one first printed circuit board carrying the at least one first metal layer and at least one second printed circuit board carrying the at least one second metal layer; wherein the at least one first printed circuit board and the at least one second printed circuit board are embedded in the laminate.

This has the following advantages: i.e. the multi-layer PCB may be a single PCB structure, i.e. the laminate. Embedding lateral and/or planar insulating layers and corresponding first and second metal layers in the laminate reduces the gap/creepage distance, thereby achieving a compact design and higher power density. In addition, wider HV traces may also be implemented, thereby reducing AC resistance, which in turn further increases power density and efficiency.

In one exemplary implementation of the multilayer printed circuit board, the laminate forms a single printed circuit board structure embedded in the multilayer printed circuit board.

This has the following advantages: i.e., embedding the multi-layer PCB reduces the gap/creepage distance, thereby achieving a compact design and higher power density; HV traces (e.g., formed from the second metal layer) may be implemented to reduce AC resistance, which in turn increases power density and efficiency.

In one exemplary implementation of the multilayer printed circuit board, the multilayer printed circuit board includes: at least one first via filled with a conductive material for electrically connecting one first metal layer with an external metal layer and/or with another first metal layer of the at least one first metal layer; and/or at least one second via filled with a conductive material for connecting one second metal layer with an external metal layer and/or with another second metal layer of the at least one second metal layer.

This has the following advantages: i.e. different vias can be flexibly routed throughout the multi-layer PCB, thereby allowing design flexibility.

The vias may be internal vias that connect the top and bottom layers of a single PCB layer within the multi-layer PCB. The vias may also be external vias that connect one or more layers of one or more PCBs with external metal layers. The inner vias may interconnect with the outer vias.

In one exemplary implementation of the multilayer printed circuit board, the at least one first metal layer is used to form a winding of a first transformer; the at least one second metal layer is used to form a winding of a second transformer.

This has the following advantages: i.e. planar transformers, may be realized by such a multilayer PCB. The planar transformer may be applied to HV/LV applications, simplifying design complexity by using a single structural PCB instead of two separate PCBs.

In one exemplary implementation of the multilayer printed circuit board, the second voltage range is higher or at least an order of magnitude higher than the first voltage range.

This has the following advantages: that is, the multi-layer PCB may be efficiently used for high-voltage (HV) and/or high-power (HP) applications, such as high-voltage generators (e.g., capacitor charging, pulsers, etc.); an isolated gate drive power supply for the medium voltage converter; a power supply, such as a solar rooftop DC-DC converter, connects the HV and LV circuits.

In one exemplary implementation of the multilayer printed circuit board, the planar insulating layer comprises one or a combination of polymer-based and ceramic-based insulating materials; wherein the planar insulating layer is of a material different from at least one of a printed circuit board carrying the at least one first metal layer or a printed circuit board carrying the at least one second metal layer or a laminate layer of the multilayer printed circuit board.

This has the following advantages: i.e. said material of said planar insulating layer has improved isolation properties compared to the usual materials used in PCBs.

According to a second aspect, the invention relates to a planar transformer comprising: a multilayer printed circuit board according to the first aspect; a magnetic core at least partially surrounding the multilayer printed circuit board.

Such planar transformers are characterized by high power density, significantly reduced height (i.e., low profile), greater surface area (thereby improving heat dissipation capability), greater magnetic cross-sectional area (thereby reducing the number of turns), smaller winding area, winding structure that facilitates interleaving, lower leakage inductance (due to reduced number of turns and interleaving of windings), smaller AC winding resistance, and excellent reproducibility (achieved by winding structure).

According to a third aspect, the invention relates to a method of manufacturing a multilayer printed circuit board for a planar transformer, the method comprising: providing a multilayer stack comprising a bottom surface, a top surface opposite the bottom surface, and at least one side surface, the multilayer stack comprising: at least one first metal layer disposed over the bottom surface in the multi-layer stack, the at least one first metal layer for conducting electrical current, wherein the at least one first metal layer is for operating in a first voltage range; at least one second metal layer disposed over the at least one first metal layer in the multi-layer stack, the at least one second metal layer for conducting electrical current, wherein the at least one second metal layer is for operating within a second voltage range that is at least partially different from the first voltage range; laminating the multilayer stack to form the multilayer printed circuit board having at least one planar insulating layer in the multilayer stack prior to laminating the multilayer stack; and/or adding at least one lateral insulating layer in the multilayer printed circuit board after lamination of the multilayer stack; wherein the planar insulating layer is formed between the at least one first metal layer and the at least one second metal layer in the multilayer stack, the at least one planar insulating layer being for electrically isolating and insulating the at least one first metal layer from the at least one second metal layer; wherein the at least one lateral insulating layer is formed between the at least one second metal layer and the at least one side in the multilayer printed circuit board, the lateral insulating layer being for electrically isolating and insulating the at least one second metal layer from a lateral environment of the at least one second metal layer.

Such a method has the same advantages as the above-described multi-layer PCB. That is, by such methods, planar transformers can be manufactured that are characterized by high power density, significantly reduced height (i.e., low profile), greater surface area (thereby improving heat dissipation capability), greater magnetic cross-sectional area (thereby reducing the number of turns), smaller winding area, winding structure that facilitates interleaving, lower leakage inductance (due to reduced number of turns and winding interleaving), smaller AC winding resistance, and excellent reproducibility (achieved by winding structure).

In one exemplary implementation of the method, providing the multilayer stack comprises: providing at least one first printed circuit board and at least one second printed circuit board; constructing the at least one first printed circuit board to form the at least one first metal layer at the at least one first printed circuit board; constructing the at least one second printed circuit board to form the at least one second metal layer at the at least one second printed circuit board; stacking the at least one first printed circuit board and the at least one second printed circuit board with the planar insulating layer between the at least one first printed circuit board and the at least one second printed circuit board to form the multi-layer stack.

This has the following advantages: i.e. these process steps correspond to the process steps of a standard PCB. These process steps may be easily adapted to manufacture the multi-layer PCB.

The structuring may comprise process steps of drilling, electroplating, photolithographic processing and/or etching.

In one exemplary implementation of the method, forming the lateral insulating layer includes: routing a slot between the at least one second metal layer and the at least one side in the multilayer printed circuit board; filling the slots with insulating material or placing pre-formed insulation into the slots to form the lateral insulating layers.

This has the following advantages: i.e. these process steps can be easily performed as they are available in standard PCB manufacturing.

Isolation may also be accomplished by a preform (the preform is placed and secured in the slot).

In one exemplary implementation of the method, the slot is routed from the top surface to the planar insulating layer or from the top surface to the bottom surface of the multilayer printed circuit board.

This has the following advantages: i.e. the slots for the lateral insulating layers can be flexibly manufactured according to the application requirements.

In one exemplary implementation of the method, the method includes: forming at least one first via extending from one first metal layer to an external metal layer and/or to another first metal layer of the at least one first metal layer; filling the at least one first via with a conductive material to electrically connect the first metal layer with the external metal layer and/or the further first metal layer; and/or forming at least one second via extending from one second metal layer to an external metal layer and/or to another second metal layer of the at least one second metal layer; the at least one second via is filled with a conductive material to electrically connect the second metal layer with the outer metal layer and/or the further second metal layer.

This has the following advantages: i.e. these process steps can be easily performed as they can be obtained from standard PCB manufacturing.

According to a fourth aspect, the invention relates to a computer program product comprising: computer-executable code or computer-executable instructions which, when executed, cause at least one computer to perform a method according to the third aspect described above.

The computer program product may be run on a controller of a manufacturing machine or robot for manufacturing a multi-layer PCB according to the first aspect by using the method according to the third aspect.

According to a fourth aspect, the present invention relates to a computer readable medium storing instructions which, when executed by a computer, cause the computer to perform a method according to the third aspect above. Such computer readable media may be non-transitory readable storage media. The instructions stored on the computer readable medium may be executed by a controller or processor of a manufacturing machine or robot for manufacturing a multi-layer PCB according to the first aspect by using the method according to the third aspect.

Drawings

Other embodiments of the invention will be described in conjunction with the following drawings, in which:

fig. 1 shows a cross-sectional view of a multilayer printed circuit board 100 provided by the present invention;

fig. 2 shows a cross-sectional view of a planar transformer 200 provided by the present invention;

fig. 3a, 3b and 3c illustrate steps of the method for manufacturing a multilayer printed circuit board 100 provided by the present invention;

FIG. 4 illustrates cross-sectional views 400a, 400c and top views 400b, 400d of a multi-layer printed circuit board 100 with ubiquitous insulation provided by one embodiment, before construction 400a, 400b and after construction 400c, 400d;

FIG. 5 illustrates cross-sectional views 500a, 500c and top views 500b, 500d of a multilayer printed circuit board 100 with partial insulation provided by one embodiment prior to construction 500a, 500b and after 500c, 500d;

fig. 6 shows a cross-sectional view of a planar transformer 600 comprising a multilayer printed circuit board 100 and a magnetic core 201 provided by the present invention;

fig. 7 shows a schematic diagram of a method 700 for manufacturing a multilayer printed circuit board 100 provided by the present invention.

Detailed Description

The following detailed description is made in conjunction with the accompanying drawings, which are a part of the description and which illustrate, by way of illustration, specific aspects in which the invention may be practiced. It is to be understood that other aspects may be utilized and structural or logical changes may be made without departing from the scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims.

It will be appreciated that the comments pertaining to the described method apply equally as well to the corresponding device or system for performing the method and vice versa. For example, if specific method steps are described, the corresponding apparatus may comprise means for performing the described method steps, even if such means are not explicitly described or shown in the figures. Furthermore, it is to be understood that features of various exemplary aspects described herein may be combined with each other, unless explicitly stated otherwise.

The new solution requires a single PCB structure with embedded HV planes and/or lateral insulation. While planar HV insulation reduces the distance between the HV and LV traces, lateral insulation reduces the gap and creepage distance from the HV winding to the transformer body (core). Lateral insulation may be used for applications with a magnetic core (fig. 2) or without a magnetic core (fig. 1). In general, this may help reduce creepage distance and clearance requirements of the HV-PCB.

The new solution can be based on planar insulation or lateral insulation, as well as planar insulation and lateral insulation.

The general structure of the new solution is shown in fig. 1 and 2. The HV PBC trace is separated from the LV trace by a local (planar) insulating layer. In addition, lateral insulation may be included that protects the core and reduces creepage and clearance distances required to ensure safety. The top and bottom layers may also be insulating. Thus, the HV trace may be completely surrounded by insulating material.

Hereinafter, the LV and HV traces are described using the more general terms "first metal layer operating in a first voltage range" and "second metal layer operating in a second voltage range". The second voltage range (HV) differs from the first voltage range (LV) in that the second voltage range is at least partially different from the first voltage range.

Fig. 1 shows a cross-sectional view of a multilayer printed circuit board 100 provided by the present invention.

The multi-layer printed circuit board 100 may be used in a planar transformer, for example, a planar transformer 200 as shown in fig. 2. Alternatively, the planar transformer may be formed using the multi-layered printed circuit board 100 without any magnetic core, or may be formed using any magnetic material attached to the multi-layered printed circuit board 100.

The multilayer printed circuit board 100 includes: a bottom surface 101; a top surface 102 opposite to the bottom surface 101; at least one side 103 (e.g., there may be four sides 103).

The multilayer printed circuit board 100 includes: at least one first metal layer 110 embedded above the bottom surface 101 in the multilayer printed circuit board 100; at least one second metal layer 120 embedded over the at least one first metal layer 110 in the multilayer printed circuit board 100; at least one planar insulating layer 130 and/or at least one lateral insulating layer 140. That is, the multilayer printed circuit board 100 may have both the planar insulating layer 130 and the lateral insulating layer 140. Alternatively, only the planar insulating layer 130 may be implemented. Alternatively, only the lateral insulating layer 140 may be implemented.

The at least one first metal layer 110 is for conducting current and for operating in a first voltage range. The at least one second metal layer 120 is for conducting current and for operating in a second voltage range. The second voltage range is at least partially different from the first voltage range. In the most relevant implementations, the first voltage range is a Low Voltage (LV) range or a Medium Voltage (MV) range, and the second voltage range is a High Voltage (HV) range.

At least one planar insulating layer 130 is embedded between at least one first metal layer 110 and at least one second metal layer 120 in the multilayer printed circuit board 100. The at least one planar insulating layer 130 is used to electrically isolate and insulate the at least one first metal layer 110 from the at least one second metal layer 120.

At least one lateral insulating layer 140 is embedded between at least one second metal layer 120 in the multilayer printed circuit board 100 and at least one side 103 of the multilayer printed circuit board 100. The at least one lateral insulating layer 140 is used to electrically isolate and insulate the at least one second metal layer 120 from the lateral environment 106 of the at least one second metal layer 120.

The multilayer printed circuit board 100 may also be part of a large PCB board having other features and parts.

For example, the lateral insulating layer 140 may extend at least in a portion transverse to the at least one second metal layer 120.

The multilayer printed circuit board may include: a top insulating layer 121 is formed at the top surface 102 of the multilayer printed circuit board 100. The at least one second metal layer 120 may be at least partially surrounded by insulating material of the top insulating layer 121, the planar insulating layer 130, and the lateral insulating layer 140.

The multilayer printed circuit board 100 may include: laminate 105 includes at least one first printed circuit board 112 carrying at least one first metal layer 110 and at least one second printed circuit board 122 carrying at least one second metal layer 120. At least one first printed circuit board 112 and at least one second printed circuit board 122 are embedded in the laminate 105.

In fig. 1, there are two first printed circuit boards 112 and 112b and two second printed circuit boards 122 and 122b. However, any other number of first and second printed circuit boards may be used. The number of first printed circuit boards may be different from the number of second printed circuit boards.

The planar insulating layers 130 and 140 effectively separate the top and bottom sides of the PCB boards 112, 122 from each other (electrically isolating and separating the top and bottom). Although all of the PCB layers 112, 112b, 122b shown in fig. 1 are isolated, the additional layers (i.e., the planar insulating layer 130) enhance isolation (i.e., electrical isolation and electrical insulation).

The laminate 105 may form a single printed circuit board structure embedded in a multi-layer printed circuit board.

The multilayer printed circuit board 100 may include at least one first via 501 filled with a conductive material (e.g., as shown in fig. 3b, 3c, 4, and 5). The at least one first via 501 is used to electrically connect one first metal layer 110 with an external metal layer 503 (e.g., as shown in fig. 3 c) and/or with another first metal layer 110b of the at least one first metal layer 110, 110b (e.g., as shown in fig. 3 c).

The multilayer printed circuit board 100 may include at least one second via 502 filled with a conductive material. At least one second via 502 is used to connect one second metal layer 120 with an external metal layer 504 and/or with another second metal layer 120b of the at least one second metal layer 120, 120b (e.g., as shown in fig. 3 c).

At least one first metal layer 110 may be used to form windings of a first transformer and at least one second metal layer 120 may be used to form windings of a second transformer.

The second voltage range may be higher than the first voltage range. In particular, the second voltage range may be at least an order of magnitude higher than the first voltage range.

For example, the first voltage range may be a low-voltage (LV) range, such as below 1500V. The second voltage range may be a high-voltage (HV) range, for example above 100kV.

In another example, the first voltage range may be a medium-voltage (MV) range, for example between 1500V and 100kV. The second voltage range may be a high-voltage (HV) range, for example above 100kV.

In another example, the first voltage range may be a low-voltage (LV) range, for example, less than 1500V. The second voltage range may be a medium-voltage (MV) range, for example between 1500V and 100kV.

The planar insulating layer 130 may be of a material different from that of at least one of the printed circuit board 112 carrying the at least one first metal layer 110 or the printed circuit board 122 carrying the at least one second metal layer 120 or the laminate 307 of the multilayer printed circuit board 100.

The planar insulating layer 130 may include one of polymer-based and ceramic-based insulating materials or a combination thereof.

The materials used for such structures (i.e., the multilayer printed circuit board 100) may be selected according to the voltage requirements of the current application.

For embedding the planar insulating layer 130, a standard multilayer PCB process of known high quality may be used. These can be applied to polymer-based and ceramic-based materials. For example, among polymer-based materials, polyimide is recommended as a candidate material because of its very sufficient adhesiveness with respect to a general PCB material (for example, FR 4). Polyimide is particularly important because of its good aging properties, flexibility, and high electrical breakdown voltage (about 900V/mil). Such materials are commonly used for semi-flexible PCBs.

The insulating material may also be based on a high voltage polyimide film (High Voltage Polyimide Film, HVPF), a very specific printed circuit material developed by Sierra, with dielectric breakdown exceeding 3000V/mil.

The insulating material may be used as a stand-alone thin material or may be inserted into a sheet of FR4 material to enhance voltage characteristics. Other insulating materials may be based on Teflon or BT epoxy with a dielectric breakdown of about 1300V/mil.

When a ceramic insulator is used, adhesion to FR4 can be improved by an adhesion promoter such as a silane coating. Other types of polymeric materials and multi-layer materials may also be used. The material must meet two main requirements. The isolation performance must remain good and stable throughout the life of the product and the material must be compatible with the PCB material and PCB process.

The type and size of the insulating material can be chosen according to the requirements of standard IEC 60664-1 (for example, table 9 describing the requirements for the pulse withstand voltage and the temporary overvoltage for the system voltage, table 11 describing the creepage distance requirements (mm) for functional insulation, basic insulation or auxiliary insulation, and/or table 10 describing the clearance distance requirements for functional insulation, basic insulation or auxiliary insulation), or according to standard IPC-2221B describing the required FR4 thickness requirements for different operating voltages.

For lateral insulation, different techniques may be used to apply the insulation material, such as printing (liquid), lamination (thermosetting, thermoplastic), wire (film, foil, preform), dispensing or other suitable process. According to the method, a variety of materials may be used. Suitable candidate materials are silicone rubber, polyimide, fluoropolymers, preforms, release adhesive sheets (e.g., namics TC1203 or similar materials), or molded resin sheets. To avoid possible voids, vacuum lamination, vacuum printing, or a separate vacuum treatment process (e.g., a similar process used in the via filling process) may be used in some cases. All of the proposed processes are normal processes commonly used in the PCB or packaging industry and thus can be easily introduced and used in combination with the processes described in the present invention.

Fig. 2 shows a cross-sectional view of a planar transformer 200 provided by the present invention.

Planar transformer 200 includes multilayer printed circuit board 100 described above in connection with fig. 1; and a magnetic core 201 at least partially surrounding the multilayer printed circuit board 100. The magnetic core 201 may be implemented as a closed shape extending through one or more holes in the multilayer printed circuit board 100.

The at least one first metal layer 110 may form a closed shape around the magnetic core 201 within the multi-layer printed circuit board 100. Similarly, at least one second metal layer 120 may form a closed shape around magnetic core 201 within multilayer printed circuit board 100.

For example, the magnetic core 201 may be formed in the shape of an 8 having two portions surrounding respective portions of the multi-layer printed circuit board 100, wherein a middle portion of the 8 extends through a hole in the multi-layer printed circuit board 100, which may be located at a central position of the multi-layer printed circuit board 100.

Such planar transformers 200 are characterized by high power density, significantly reduced height (i.e., low profile), greater surface area (thereby improving heat dissipation capability), greater magnetic cross-sectional area (thereby reducing the number of turns), smaller winding area, winding structure that facilitates interleaving, lower leakage inductance (due to reduced number of turns and winding interleaving), smaller AC winding resistance, and excellent reproducibility (achieved by winding structure).

The planar transformer 200 can meet the requirements of pulse withstand voltage and temporary overvoltage on system voltage, creepage distance requirements of functional insulation, basic insulation or auxiliary insulation and clearance distance requirements of functional insulation, basic insulation or auxiliary insulation according to standard IEC 60664-1 of different working voltages.

The planar transformer 200 can withstand high voltages during normal operation and commissioning (insulation withstand voltage test and pulse test). Can meet the typical voltage insulation requirement specified by the standard IEC 62477-1. For example, planar transformers are capable of withstanding pulse voltages between 4kV and 12kV and even higher when operated at 1 kVdc.

Fig. 3a, 3b and 3c illustrate the manufacturing steps of the method for manufacturing a multilayer printed circuit board 100 provided by the present invention.

The manufacturing method, also called process flow, is shown in connection with the manufacturing steps 1) to 10) in fig. 3a, 3b and 3c and is described in detail below. The process begins with the manufacture of several standard 2-layer PCBs according to standard simplified PCB process flows: 1) drilling, 2) electroplating, and 3) photolithography and etching, as shown in fig. 3 a.

These layers (two or more) are then stacked together with an insulating layer 307 in a manufacturing step 4) to form a multi-layer stack 304 (typically FR4, but also different materials if different properties are required for the final product) and with additional insulating layers 307 and copper foil 308 on the top side 102 and bottom side 101, as shown in fig. 3 a. This is optional, as may be required if vias are required between the layers.

Then, in manufacturing step 5), referring to fig. 3b, the multilayer stack 304 is laminated in a vacuum lamination press to form a unitary structure. For example, the unitary structure may include a first PCB 122b (e.g., a 2-layer PCB), a second PCB 122 (e.g., a 2-layer PCB), a third PCB 112 (e.g., a 2-layer PCB), and a fourth PCB 112b (e.g., a 2-layer PCB). The at least one first metal layer 110 may be any one of the layers of the third PCB 112 or the fourth PCB 112 b. The at least one second metal layer 120 may be any one of the layers of the first PCB 122b or the second PCB 122.

Then, in a manufacturing step 6), mechanical or laser drilling may be performed to drill vias 401, 402 between the selected layers. These holes 401, 402 may be drilled to a certain depth from the top side 102 or the bottom side 101, or may be drilled to a certain depth over the entire PCB, e.g. as shown in the first PCB 122b and the fourth PCB 112b, see fig. 3b.

Then, in manufacturing step 7), electroless and electrochemical plating will be used to fill the holes 401, 402 with conductive material to form the through holes 501, 502, see fig. 3b. Up to now, planar insulation can be ensured. If lateral isolation is not required, the process flow will stop here. Otherwise, in process step 8), slot routing is performed to create slots 403, 404 for lateral isolation. These slots 403, 404 may be routed throughout the PCB stack, or may be routed only for the portion corresponding to the HV winding.

Then, in a manufacturing step 9), the slots 403, 404 are filled with an insulating material to form the lateral insulating layer 140, see fig. 3c. This may be accomplished by printing, lamination, dispensing, or other suitable process. To minimize the risk of void formation, vacuum lamination, vacuum printing or additional vacuum treatments may be used. If desired, in process step 10), a stencil or screen printing process may be used, but etching and structuring processes may also be used, the insulating material being removed from unwanted areas of the PCB by water spraying, plasma cleaning, mechanical brushing, chemical cleaning or other similar processes, see fig. 3c. These are standard processes for normal PCB processing (e.g., via filling). Other types of PCB processes may be used to manufacture HV and LV layers and end products in addition to the processes described above.

The application of lateral insulation 140 may be limited to a specific area of the PCB (as shown in fig. 5) or may be applied to the entire PCB (as shown in fig. 4). The latter application is preferred because it simplifies the process flow.

Fig. 4 illustrates cross-sectional views 400a, 400c and top views 400b, 400d of a multi-layer printed circuit board 100 with ubiquitous insulation provided by one embodiment, before construction 400a, 400b and after construction 400c, 400d.

Left side diagrams 400a, 400c show cross-sectional views of the single structure multi-layer PCB 100, while right side diagrams 400b, 400d show top views of the single structure multi-layer PCB 100. In diagrams 400a, 400b, holes 403, 404 for lateral insulation layers are shown; the PCB is constructed, for example, corresponding to manufacturing step 8 of fig. 3 b. In graphs 400c, 400d, holes 403, 404 are filled with conductive material forming lateral insulating layer 140; the PCB is completed, for example, corresponding to manufacturing step 10 of fig. 3 c.

In this example, the single structure multilayer printed circuit board 100 includes a first portion, e.g., an HV portion, having a first PCB 122b (e.g., a 2-layer PCB) and a second PCB 122 (e.g., a 2-layer PCB), the HV portion having respective HV traces corresponding to the at least one second metal layer 120 described above in connection with fig. 1.

The single structure multilayer printed circuit board 100 includes a second portion, e.g., an LV portion, having a third PCB 112 (e.g., a 2-layer PCB) and a fourth PCB 112b (e.g., a 2-layer PCB), the LV portion having respective LV traces corresponding to the at least one first metal layer 110 described above in connection with fig. 1.

The first and second portions are isolated from each other by the planar insulating layer 130 described above in connection with fig. 1 and from the lateral environment by the lateral insulating layer 140 described above in connection with fig. 1. Lateral insulating layer 140 is as described above in connection with fig. 1. Lateral insulating layer 140 extends from top side 102 to bottom side 101 and provides ubiquitous insulation.

Fig. 5 illustrates cross-sectional views 500a, 500c and top views 500b, 500d of a multilayer printed circuit board 100 with partial insulation provided by one embodiment prior to construction 500a, 500b and after 500c, 500d.

Left side diagrams 500a, 500c show cross-sectional views of the single structure multi-layer PCB 100, while right side diagrams 500b, 500d show top views of the single structure multi-layer PCB 100. In graphs 500a, 500b, holes 403, 404 for lateral insulating layers are shown; the PCB is constructed, for example, corresponding to manufacturing step 8 of fig. 3 b. In graphs 500c, 500d, holes 403, 404 are filled with conductive material forming lateral insulating layer 140; the PCB is completed, for example, corresponding to manufacturing step 10 of fig. 3 c.

As described above in connection with fig. 4, the single structure multilayer printed circuit board 100 includes a first portion and a second portion. The first and second portions are isolated from each other by the planar insulating layer 130 described above in connection with fig. 1 and from the lateral environment by the lateral insulating layer 140 described above in connection with fig. 1. Lateral insulating layer 140 is as described above in connection with fig. 1. Lateral insulating layer 140 extends from top side 102 down to planar insulating layer 130 instead of bottom side 101. Lateral insulating layer 140 provides localized insulation.

Fig. 6 shows a cross-sectional view of a planar transformer 600 comprising a multilayer printed circuit board 100 and a magnetic core 201 provided by the present invention.

Planar transformer 600 includes multilayer printed circuit board 100 described above in connection with fig. 1; and a magnetic core 201 at least partially surrounding the multilayer printed circuit board 100 as described above in connection with fig. 2. The magnetic core 201 may be implemented as a closed shape extending through one or more holes in the multilayer printed circuit board 100.

The electrical devices 601, 602 may be connected to the first metal layer 110 and the second metal layer 120.

The conventional planar transformer needs to have a structure having two separate PCBs with enough space therebetween in order to meet the gap and creepage distance requirements, in contrast to the novel planar transformer 600 which may be implemented as a single PCB structure. Such a single PCB structure may be designed to meet the gap and creepage distance requirements.

Compared to a traditional double-PCB structure, the novel single-PCB structure can have wider HV traces, thereby reducing AC resistance, shortening gaps, and creepage distances. With the novel single PCB structure, easier interconnection between the LV and HV portions can be achieved and a thinner planar insulating layer 130 can be applied than required for a conventional double PCB structure.

Planar transformer 600 is characterized by high power density, significantly reduced height (i.e., low profile), greater surface area (thereby improving heat dissipation), greater magnetic cross-sectional area (thereby reducing the number of turns), smaller winding area, winding structure that facilitates interleaving, lower leakage inductance (due to reduced number of turns and winding interleaving), smaller AC winding resistance, and excellent reproducibility (achieved by the winding structure).

The method 700 includes providing 701 a multilayer stack 304, for example, as shown in fig. 3 a. The multilayer stack 304 includes a bottom surface 101, a top surface 102 opposite the bottom surface 101, and at least one side surface 103.

The multilayer stack 304 includes: at least one first metal layer 110 disposed over the bottom surface 101 in the multilayer stack 304; at least one second metal layer 120 is placed over at least one first metal layer 110 in the multilayer stack 304, for example, as shown in fig. 3 a.

The at least one first metal layer 110 is for conducting current and for operating in a first voltage range. The at least one second metal layer 120 is for conducting current and for operating in a second voltage range, which is at least partially different from the first voltage range.

Method 700 includes laminating (702) a multilayer stack 304, for example, as shown in fig. 3b, to form a multilayer printed circuit board 100 having at least one planar insulating layer 130 in the multilayer stack 304 prior to laminating the multilayer stack 304; and/or adding at least one lateral insulating layer 140 to the multilayer printed circuit board 100 after lamination of the multilayer stack 304. That is, the multi-layered printed circuit board 100 with or without the lateral insulating layer 140 may be manufactured.

A planar insulating layer 130 is formed (703) between the at least one first metal layer 110 and the at least one second metal layer 120 in the multilayer stack 304. The at least one planar insulating layer 130 is used to electrically isolate and insulate the at least one first metal layer 110 from the at least one second metal layer 120, e.g., as described above in connection with fig. 1-5.

At least one lateral insulating layer 140 is formed (703) between the at least one second metal layer 120 and the at least one side 103 in the multilayer printed circuit board 100. The lateral insulating layer 140 serves to electrically isolate and insulate the at least one second metal layer 120 from the lateral environment 106 of the at least one second metal layer 120, e.g., as described above in connection with fig. 1-5.

Providing (701) the multilayer stack 304 may comprise the following manufacturing steps:

Providing at least one first printed circuit board 112 and at least one second printed circuit board 122;

constructing at least one first printed circuit board 112 to form at least one first metal layer 110 at the at least one first printed circuit board 112;

constructing at least one second printed circuit board 122 to form at least one second metal layer 120 at the at least one second printed circuit board 112;

the at least one first printed circuit board 112 and the at least one second printed circuit board 122 are stacked such that the planar insulating layer 130 is located between the at least one first printed circuit board 112 and the at least one second printed circuit board 122 to form a multi-layer stack 304.

Forming (703) the lateral insulating layer 140 may include the following manufacturing steps:

routing the slots between at least one second metal layer 120 and at least one side 103 in the multilayer printed circuit board 100, e.g., as described above in connection with manufacturing step 8) of fig. 3 b;

filling the socket with insulating material or placing a pre-formed insulator into the socket to form lateral insulating layer 140, for example, as described above in connection with manufacturing step 9) of fig. 3 c.

The slots may be routed from the top surface 102 to the planar insulating layer 130 (as shown in fig. 5) or from the top surface 102 to the bottom surface 101 (as shown in fig. 4) of the multilayer printed circuit board 100.

The method 700 may include:

forming at least one first via 501, e.g. as shown in step 6) and step 7) of fig. 3b, the at least one first via 501 extending from one first metal layer 110 to an outer metal layer 503 and/or to the other first metal layer 110b of the at least one first metal layer 110, 110b;

filling at least one first via 501 with a conductive material, for example, as shown in step 7) of fig. 3b, to electrically connect the first metal layer 110 with the external metal layer 503 and/or another first metal layer 110b; and/or

Forming at least one second via 502, e.g. as shown in step 6) and step 7) of fig. 3b, the at least one second via 502 extending from one second metal layer 120 to an outer metal layer 504 and/or to the other second metal layer 120b of the at least one second metal layer 120, 120b;

the at least one second via 502 is filled with a conductive material, for example as shown in step 7) of fig. 3b, to electrically connect the second metal layer 120 with the outer metal layer 503 and/or another second metal layer 120 b.

While a particular feature or aspect of the invention may have been disclosed with respect to only one of several implementations, such feature or aspect may be combined with one or more other features or aspects of the other implementations as may be desired and advantageous for any given or particular application. Furthermore, to the extent that the terms "includes," has, "or other variants of those terms are used in either the detailed description or the claims, such terms and" comprising "are intended to be inclusive in a manner similar to the term" comprising. Also, the terms "exemplary," "such as," and "for example," are merely meant as examples, rather than as being best or optimal. The terms "coupled" and "connected," along with their derivatives, may be used. It should be understood that these terms may be used to indicate that two elements co-operate or interact with each other regardless of whether they are in direct physical or electrical contact or they are not in direct contact with each other.

Although specific aspects have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent implementations may be substituted for the specific aspects shown and described without departing from the scope of the present invention. This application is intended to cover any adaptations or variations of the specific aspects discussed herein.

Although elements in the above claims are recited in a particular order with corresponding labeling, unless the claim recitations otherwise imply a particular order for implementing some or all of those elements, those elements are not necessarily limited to being implemented in that particular order.

Many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the above teachings. Of course, those skilled in the art will readily recognize that numerous other applications of the present invention exist in addition to those described herein. While the invention has been described with reference to one or more particular embodiments, those skilled in the art will recognize that many changes may be made to the embodiments without departing from the scope of the present invention. It is, therefore, to be understood that within the scope of the appended claims and equivalents thereof, the invention may be practiced otherwise than as specifically described herein.

Claims

1. A multilayer printed circuit board (100) for a planar transformer, the multilayer printed circuit board (100) comprising:

a bottom surface (101);

a top surface (102) opposite to the bottom surface (101);

at least one side (103);

-at least one first metal layer (110) embedded in the multilayer printed circuit board (100) above the bottom surface (101), the at least one first metal layer (110) being for conducting current, wherein the at least one first metal layer (110) is for operating in a first voltage range;

-at least one second metal layer (120) embedded over the at least one first metal layer (110) in the multilayer printed circuit board (100), the at least one second metal layer (120) being for conducting current, wherein the at least one second metal layer (120) is for operating in a second voltage range, the second voltage range being at least partially different from the first voltage range;

at least one planar insulating layer (130) and/or at least one lateral insulating layer (140);

wherein the at least one planar insulating layer (130) is embedded between the at least one first metal layer (110) and the at least one second metal layer (120) in the multilayer printed circuit board (100), the at least one planar insulating layer (130) being for electrically isolating and insulating the at least one first metal layer (110) from the at least one second metal layer (120);

Wherein the at least one lateral insulating layer (140) is embedded between the at least one second metal layer (120) in the multilayer printed circuit board (100) and the at least one side (103) of the multilayer printed circuit board (100), the at least one lateral insulating layer (140) being used for electrically isolating and electrically insulating the at least one second metal layer (120) from a lateral environment (106) of the at least one second metal layer (120).

2. The multilayer printed circuit board (100) of claim 1, wherein,

the lateral insulating layer (140) extends at least in a portion transverse to the at least one second metal layer (120).

3. The multilayer printed circuit board (100) according to claim 1 or 2, comprising:

a top insulating layer (121) formed at the top surface (102) of the multilayer printed circuit board (100);

wherein the at least one second metal layer (120) is at least partially surrounded by insulating material of the top insulating layer (121), the planar insulating layer (130) and the lateral insulating layer (140).

4. The multilayer printed circuit board (100) of any one of the preceding claims, comprising:

a laminate (105) comprising at least one first printed circuit board (112) carrying the at least one first metal layer (110) and at least one second printed circuit board (122) carrying the at least one second metal layer (120);

Wherein the at least one first printed circuit board (112) and the at least one second printed circuit board (122) are embedded in the laminate (105).

5. The multi-layer printed circuit board (100) of claim 4, wherein,

the laminate (105) forms a single printed circuit board structure embedded in a multi-layer printed circuit board.

6. The multilayer printed circuit board (100) of any one of the preceding claims, comprising:

at least one first via (501) filled with an electrically conductive material, the at least one first via (501) being for electrically connecting one first metal layer (110) with an external metal layer (503) and/or with another first metal layer (110 b) of the at least one first metal layer (110, 110 b); and/or

At least one second via (502) filled with an electrically conductive material, the at least one second via (502) being for connecting one second metal layer (120) with an external metal layer (504) and/or with another second metal layer (120 b) of the at least one second metal layer (120, 120 b).

7. The multilayer printed circuit board (100) according to any of the preceding claims, characterized in that,

the at least one first metal layer (110) is used for forming a winding of a first transformer;

The at least one second metal layer (120) is used to form a winding of a second transformer.

8. The multilayer printed circuit board (100) according to any of the preceding claims, characterized in that,

the second voltage range is higher or at least an order of magnitude higher than the first voltage range.

9. The multilayer printed circuit board (100) according to any of the preceding claims, characterized in that,

the planar insulating layer (130) comprises one or a combination of polymer-based and ceramic-based insulating materials;

wherein the planar insulating layer (130) is of a material different from the material of at least one of the printed circuit board (112) carrying the at least one first metal layer (110) or the printed circuit board (122) carrying the at least one second metal layer (120) or the laminate layer (307) of the multilayer printed circuit board (100).

10. A planar transformer (200), characterized by comprising:

the multilayer printed circuit board (100) according to any one of the preceding claims;

-a magnetic core (201) at least partially surrounding the multilayer printed circuit board (100).

11. A method of manufacturing a multilayer printed circuit board (100) for a planar transformer, the method comprising:

Providing a multilayer stack (304), the multilayer stack (304) comprising a bottom surface (101), a top surface (102) opposite the bottom surface (101), and at least one side surface (103), the multilayer stack (304) comprising:

-at least one first metal layer (110) placed over the bottom surface (101) in the multilayer stack (304), the at least one first metal layer (110) being for conducting a current, wherein the at least one first metal layer (110) is for operating in a first voltage range;

-at least one second metal layer (120) placed over the at least one first metal layer (110) in the multilayer stack (304), the at least one second metal layer (120) being for conducting a current, wherein the at least one second metal layer (120) is for operating in a second voltage range, the second voltage range being at least partially different from the first voltage range;

laminating the multilayer stack (304) to form the multilayer printed circuit board (100) having at least one planar insulating layer (130) in the multilayer stack (304) prior to laminating the multilayer stack (304); and/or adding at least one lateral insulating layer (140) in the multilayer printed circuit board (100) after lamination of the multilayer stack (304);

Wherein the planar insulating layer (130) is formed between the at least one first metal layer (110) and the at least one second metal layer (120) in the multilayer stack (304), the at least one planar insulating layer (130) being for electrically isolating and electrically insulating the at least one first metal layer (110) from the at least one second metal layer (120);

wherein the at least one lateral insulating layer (140) is formed between the at least one second metal layer (120) and the at least one side (103) in the multilayer printed circuit board (100), the lateral insulating layer (140) being for electrically isolating and insulating the at least one second metal layer (120) from a lateral environment (106) of the at least one second metal layer (120).

12. The method of claim 11, wherein providing the multi-layer stack (304) comprises:

providing at least one first printed circuit board (112) and at least one second printed circuit board (122);

-structuring the at least one first printed circuit board (112) to form the at least one first metal layer (110) at the at least one first printed circuit board (112);

-structuring the at least one second printed circuit board (122) to form the at least one second metal layer (120) at the at least one second printed circuit board (112);

-stacking the at least one first printed circuit board (112) and the at least one second printed circuit board (122) with the planar insulating layer (130) between the at least one first printed circuit board (112) and the at least one second printed circuit board (122) to form the multi-layer stack (304).

13. The method of claim 11 or 12, wherein forming the lateral insulating layer (140) comprises:

routing a slot between the at least one second metal layer (120) and the at least one side (103) in the multilayer printed circuit board (100);

filling the slots with insulating material or placing pre-formed insulation into the slots to form the lateral insulating layers (140).

14. The method of claim 13, wherein the step of determining the position of the probe is performed,

the slots are routed from the top surface (102) to the planar insulating layer (130) or from the top surface (102) to the bottom surface (101) of the multilayer printed circuit board (100).

15. The method according to any one of claims 11 to 14, comprising:

-forming at least one first via (501), the at least one first via (501) extending from one first metal layer (110) to an outer metal layer (503) and/or to another first metal layer (110 b) of the at least one first metal layer (110, 110 b);

Filling the at least one first via (501) with a conductive material to electrically connect the first metal layer (110) with the outer metal layer (503) and/or the further first metal layer (110 b); and/or

-forming at least one second via (502), the at least one second via (502) extending from one second metal layer (120) to an outer metal layer (504) and/or to another second metal layer (120 b) of the at least one second metal layer (120, 120 b);

-filling the at least one second via (502) with an electrically conductive material to electrically connect the second metal layer (120) with the outer metal layer (503) and/or the further second metal layer (120 b).