Design method of PCB integrated multi-winding planar transformer

Abstract

The invention discloses a design method of a PCB (Printed Circuit Board) integrated multi-winding planar transformer, which comprises the following steps of: forming a flat spiral or snake-shaped wire, a primary winding and a secondary winding on a multi-layer PCB through an etching process; the primary winding and the secondary winding are alternately arranged in different layers of the PCB, and an even-number-layer symmetrical laminated structure is adopted for layout; a flaky soft magnetic material with high magnetic conductivity is selected as a magnetic core, and the magnetic core is embedded into the slotting area of the PCB to be fixed; a grounding shielding layer is inserted between the adjacent winding layers; a heat conduction via hole array is arranged in a winding area of the PCB, heat generated by a winding layer is conducted to a large-area heat dissipation copper foil on the bottom layer of the PCB, and a vertical heat dissipation channel is formed. According to the planar flyback transformer, the windings are etched on the multi-layer PCB, the alternating symmetrical layout is adopted, the magnetic core is embedded, and the shielding layer and the heat conduction via hole array are arranged, so that the integrated design of the planar flyback transformer is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of planar transformer design, in particular to a PCB integrated multi-winding planar transformer design method. BACKGROUND

[0002] In the existing vehicle controller power supply design, the transformer is constructed on the basis of the traditional winding transformer, adopts the plug-in transformer mode, and penetrates the flyback topology structure. Although these designs can meet the basic energy transmission requirements, they still have many problems and limitations in actual application.

[0003] Firstly, the traditional winding transformer has obvious volume and weight problems. This three-dimensional structure not only occupies a large space, but also occupies a large amount of vertical and horizontal space on the PCB board, which increases the complexity of circuit design and limits the improvement of power density. Secondly, the winding structure of the traditional transformer adopts a layered design of "primary side-insulation layer-secondary side" or a parallel winding structure of "primary side and secondary side side by side". Although this design is effective, it also causes a significant physical distance between the windings, resulting in a large leakage inductance. Due to the existence of leakage inductance, the rapidly changing leakage inductance current will cause a large electromagnetic interference to the surrounding circuit, affecting the stability of the system, and also putting forward more stringent requirements for EMC (electromagnetic compatibility) design. In addition, due to the large leakage inductance of the traditional transformer, the energy transmission loss increases, and the efficiency is relatively low. In addition, the traditional transformer mainly dissipates heat through air and solder pads, and the heat conduction performance is poor, the working temperature rise is high, and long-term operation may seriously affect the service life and reliability of the device.

[0004] In summary, not only the overall performance and efficiency of the vehicle controller power supply are affected, but also problems such as EMC design and heat dissipation are brought, which are key technical problems that need to be solved. SUMMARY

[0005] The purpose of the present application is to overcome the deficiencies of the prior art. In order to achieve the above purpose, a PCB integrated multi-winding planar transformer design method is adopted to solve the problems raised in the background technology.

[0006] A PCB integrated multi-winding planar transformer design method, comprising the following steps: Step S1, winding integration design: forming a flat spiral or serpentine trace on a multi-layer PCB board through etching process to constitute a primary winding and a secondary winding of the transformer; Step S2, multi-layer symmetrical layout design: alternately arranging the primary winding and the secondary winding in different layers of the PCB, and adopting an even layer symmetrical laminated structure for layout; Step S3, magnetic core integrated design: select a thin sheet-shaped soft magnetic material with high magnetic permeability as the magnetic core, embed it in the slotted area of the PCB, and fix it with epoxy resin; Step S4, electromagnetic compatibility design: insert a ground shielding layer between adjacent winding layers to suppress common mode noise; Step S5, heat dissipation channel design: set up a heat conduction via array in the winding area of the PCB to conduct the heat generated by the winding layer to the large-area heat dissipation copper foil at the bottom layer of the PCB, forming a vertical heat dissipation channel.

[0007] As a further scheme of the present application: in step S1, the line width and spacing of the spiral or serpentine trace are also optimized to balance the current distribution and parasitic capacitance.

[0008] As a further scheme of the present application: in step S1, the winding trace structure is designed in series to increase the turns ratio, or in parallel to increase the current carrying capacity.

[0009] As a further scheme of the present application: in step S1, the PCB copper thickness is selected according to the load current size, and 70μm thick copper is used for large current paths to reduce on-state impedance.

[0010] As a further scheme of the present application: in step S2, the multi-layer symmetrical layout design is specifically a 6-layer board structure, which is designed from top to bottom as: top layer arrangement part of primary winding, insulating dielectric layer, first secondary winding layer, internal ground shielding layer, second secondary winding layer, and bottom layer arrangement part of primary winding.

[0011] As a further scheme of the present application: in step S2, the thickness of the interlayer insulating dielectric layer is set to be less than or equal to 0.2mm.

[0012] As a further scheme of the present application: in step S3, before fixing the magnetic core, a heat-conducting insulating material with a thermal conductivity greater than 3W / m·K is applied or padded in the contact area between the magnetic core and the PCB.

[0013] As a further scheme of the present application: in step S5, the parameter design of the heat-conducting via array is: hole diameter 0.3mm, spacing 1.0mm.

[0014] As a further scheme of the present application: in step S1, the winding layout is optimized by PCB design software to ensure the shortest current path, and the leakage inductance of the transformer is controlled to be below 1μH.

[0015] As a further scheme of the present application: the operating frequency range of the planar transformer is set to 100kHz to 500kHz.

[0016] Compared with the prior art, the present application has the following technical effects: By adopting the technical scheme, highly integrated and performance optimization are realized through five key steps: firstly, a flat spiral line is made on a multilayer PCB by adopting an etching process to form a winding, instead of a traditional enameled wire; secondly, an even number of symmetric laminated designs with primary and secondary windings arranged alternately are adopted to optimize electromagnetic coupling and reduce leakage inductance; thirdly, a sheet-shaped magnetic core is embedded in the PCB and fixed; fourthly, a ground shielding layer is inserted between the winding layers to improve electromagnetic compatibility; and finally, a vertical high-efficiency heat dissipation channel from the winding to the bottom layer of the PCB is constructed by designing a heat conduction via array.

[0017] The designed transformer realizes miniaturization, light weight and high power density, and the volume and weight can be reduced by more than 50%; through the symmetric winding and shielding layer design, the leakage inductance and electromagnetic interference (EMI) are significantly reduced, and the efficiency can reach 97%-98.5%; the unique "heat conduction via + bottom copper foil" heat dissipation scheme effectively reduces the working temperature and improves the reliability; at the same time, this method eliminates the traditional winding, impregnation and other processes, and is produced by using the standard PCB process, which reduces the cost by about 30%, and is more suitable for automated manufacturing, ensuring the consistency of the product. BRIEF DESCRIPTION OF DRAWINGS

[0018] The specific embodiments of the present application will be described in detail below with reference to the accompanying drawings: Figure 1 The step schematic diagram of the transformer design method of the disclosed embodiment of the present application is shown in the figure; Figure 2 The structure diagram of the 4-layer planar transformer of the disclosed embodiment of the present application is shown in the figure; Figure 3 The structure schematic diagram of the 6-layer planar transformer of the disclosed embodiment of the present application is shown in the figure; Figure 4 The heat conduction design schematic diagram of the 6-layer planar transformer of the disclosed embodiment of the present application is shown in the figure; Figure 5 The winding structure schematic diagram of the disclosed embodiment of the present application is shown in the figure; Figure 6 The efficiency comparison diagram of the disclosed embodiment of the present application is shown in the figure. DETAILED DESCRIPTION

[0019] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the present application.

[0020] Please refer to Figure 1In the embodiment of the present application, a PCB integrated multi-winding planar transformer design method comprises the following steps: Step S1, winding integration design: on a multi-layer PCB, flat spiral or serpentine traces are formed by etching process to constitute primary winding and secondary winding of the transformer; In this embodiment, in step S1, the line width and spacing of the spiral or serpentine traces are also optimized to balance current distribution and parasitic capacitance.

[0021] In this embodiment, in step S1, the trace structure of the winding is designed in series to improve the turns ratio, or in parallel to improve the current carrying capacity.

[0022] In this embodiment, in step S1, the PCB copper thickness is selected according to the load current size, and 70μm copper thickness is used for large current path to reduce on-state impedance.

[0023] In this embodiment, in step S1, the winding layout is optimized by PCB design software to ensure the shortest current path and control the leakage inductance of the transformer below 1μH.

[0024] In this embodiment, in step S1, the winding layout is optimized by PCB design software to ensure the shortest current path and control the leakage inductance of the transformer below 1μH.

[0025] In a specific embodiment, as shown in Figure 2 The figure is a 4-layer planar transformer structure diagram; it includes a magnetic core, a spiral line design on a PCB, a primary winding, and a secondary winding; the planar transformer has no enameled wire winding, but a flat continuous copper spiral line is etched on the PCB, and then stacked on the magnetic core.

[0026] Step S2, multi-layer symmetrical layout design: the primary winding and the secondary winding are alternately arranged in different layers of the PCB, and a symmetrical laminated structure is used for layout; In this embodiment, in step S2, the multi-layer symmetrical layout design is specifically a 6-layer board structure, which is designed from top to bottom as follows: part of the primary winding is arranged on the top layer, an insulating medium layer, a first secondary winding layer, an internal ground shielding layer, a second secondary winding layer, and part of the primary winding is arranged on the bottom layer.

[0027] The magnetic core material is selected to be a soft magnetic material with high magnetic permeability, which can effectively improve the efficiency of the transformer. The magnetic core is designed in a sheet shape, which is convenient for close combination with the PCB and reduces the volume.

[0028] The primary and secondary windings of the integrated structure design transformer adopt spiral or serpentine wiring, and the current distribution and parasitic capacitance are balanced by optimizing the line width and spacing. The magnetic core adopts a split structure, is directly embedded in the slotted area of the PCB, and is fixed by epoxy resin curing; meanwhile, a heat-conducting insulating layer can be arranged between the magnetic core and the PCB to improve the heat dissipation capacity.

[0029] The electromagnetic compatibility design suppresses common-mode noise by inserting a ground shielding layer between adjacent windings; meanwhile, the interleaved winding layout is adopted to offset the eddy current loss caused by high-frequency magnetic fields.

[0030] In the specific implementation, the PCB design adopts a multi-layer PCB design, the primary windings and the secondary windings are located on different layers, and the electrical connection between the layers is realized through vias. In the PCB design software, the layout of the windings is optimized to ensure the shortest current path and reduce the loss.

[0031] The number of layers of the PCB of the planar transformer can be flexibly designed according to the number of windings, as shown in FIG. 6, which is a typical 6-layer board. The stack structure from top to bottom can be divided into: top layer (primary winding part) -- insulating medium layer (0.2mm FR4) -- secondary winding layer 1 -- internal ground shielding layer -- secondary winding layer 2 -- bottom layer (primary winding part). This symmetrical stack design helps to balance the stress, prevent the PCB from warping, and optimize the electromagnetic coupling. The thickness of the interlayer insulating medium is usually 0.2mm to meet the safety requirements, and the copper thickness can be selected as 70um (2oz) or 35um (1oz) according to the design load current size. For large current paths, 2oz copper thickness can be used to reduce the on-resistance. Figure 3 In this embodiment, in step S2, the thickness of the interlayer insulating medium layer is set to be less than or equal to 0.2mm.

[0032] Step S3, magnetic core integrated design: a thin sheet-shaped soft magnetic material with high magnetic permeability is selected as the magnetic core, and is embedded in the slotted area of the PCB, and is fixed by using epoxy resin;

[0033] In this embodiment, in step S3, before fixing the magnetic core, a heat-conducting insulating material with a thermal conductivity greater than 3W / m·K is coated or padded in the contact area between the magnetic core and the PCB. Step S4, electromagnetic compatibility design: a ground shielding layer is inserted between adjacent winding layers to suppress common-mode noise;

[0034] Step S5, heat dissipation channel design: a heat-conducting via array is arranged in the winding area of the PCB, and the heat generated by the winding layer is conducted to the large-area heat dissipation copper foil at the bottom of the PCB to form a vertical heat dissipation channel.

[0035] ​In this embodiment, the parameters of the heat-conducting via array in step S5 are designed as follows: hole diameter 0.3 mm, and spacing 1.0 mm.

[0036] In this embodiment, the working frequency range of the planar transformer is set to 100 kHz to 500 kHz.

[0037] Specifically, the current carrying density of the PCB integrated planar transformer can reach up to 20 A / mm2; if 2 oz copper foil is used, the width of a single wire is designed to be 2 mm. Its area A = width * thickness = 2 mm * 0.07 mm = 0.14 mm2. According to the IPC-2152 standard (allowable temperature rise ΔT = 40°C), the wire with this cross-sectional area can continuously carry a current of about 2.8 A.

[0038] Therefore, the current carrying density J = I / A = 2.8 A / 0.14 mm2≈20 A / mm2. This value is significantly higher than that of traditional round wire enameled wire (usually <10 A / mm2).

[0039] Around and below the winding area, a dense heat-conducting via array (hole diameter 0.3 mm, spacing 1.0 mm) is arranged, which efficiently conducts the heat generated by the winding layer to the large-area copper foil (ground layer or special heat dissipation pad) on the PCB bottom layer, and then contacts the metal shell or heat sink through heat-conducting silicone, forming a vertical heat dissipation main channel.

[0040] The area where the magnetic core contacts the PCB is coated or padded with high-thermal-conductivity insulating material (such as heat-conducting silicone or aluminum nitride ceramic sheet, thermal conductivity > 3 W / m·K), which directly conducts the heat generated by the magnetic core during operation to the PCB and uses the above-mentioned internal heat dissipation path of the PCB to dissipate the heat, as shown in Figure 4 The figure is a heat-conducting design schematic diagram of a 6-layer planar transformer. The winding is made and structured using PCB etching process, which ensures the accuracy and consistency of the winding. The winding structure can be designed as series type (to increase the turns ratio) or parallel type (to increase the current capacity) according to requirements, as shown in Figure 5 The figure is a winding structure schematic diagram. Cost and manufacturability optimization: To control costs, the inner copper thickness is recommended to be no more than 3 oz (105 um), and the dielectric layer thickness is as uniform as possible and no more than 0.2 mm, so as to use low-cost machine drilling process to make vias, reduce mechanical drilling and multiple pressing processes, and widen the thickness tolerance of the multi-layer board to ±10%, thereby improving the production yield.

[0041] Advantages of the present application: As shown in Figure 6 The figure is an efficiency comparison chart. ①By integrating windings on PCB and using thin magnetic core, the volume and weight can be reduced by more than 50% compared with traditional wound transformer, greatly improving the power density and layout flexibility.

[0042] ②The precise windings based on PCB make the leakage inductance controllable below 1 μH (5-10 μH for traditional transformer), significantly reducing the switching loss and electromagnetic interference (EMI). By built-in ground shielding layer, the EMC performance is further optimized.

[0043] ③The simulation and measured data shown in the following figure show that the efficiency of the present scheme can be stabilized at 97%-98.5% at a typical working frequency (such as 100kHz-500kHz), which is significantly improved compared with the traditional transformer (peak efficiency about 95%).

[0044] Although embodiments of the present application have been shown and described, it is to be understood that various modifications, substitutions, replacements and changes can be made to these embodiments without departing from the principles and spirit of the present application, the scope of the present application is defined by the appended claims and their equivalents, and all should be included within the protection scope of the present application.

Claims

1. A PCB integrated multi-winding planar transformer design method, characterized by, The method comprises the following steps: Step S1, winding integration design: forming flat spiral or serpentine traces on a multi-layer PCB to constitute primary and secondary windings of a transformer through an etching process; Step S2, multi-layer symmetrical layout design: alternately arranging the primary and secondary windings in different layers of the PCB and adopting an even-layer symmetrical laminated structure for layout; Step S3, magnetic core integration design: selecting a thin sheet-shaped soft magnetic material with high magnetic permeability as a magnetic core and embedding the magnetic core in a slotted area of the PCB and fixing the same using epoxy resin; Step S4, electromagnetic compatibility design: inserting a ground shielding layer between adjacent winding layers to suppress common-mode noise; Step S5, heat dissipation channel design: arranging a heat-conducting via array in the winding area of the PCB to conduct heat generated by the winding layers to a large-area heat-dissipating copper foil at the bottom layer of the PCB to form a vertical heat dissipation channel.

2. The method of claim 1, wherein the PCB integrated multi-winding planar transformer design method is characterized by, In the step S1, the line width and spacing of the spiral or serpentine traces are optimized to balance current distribution and parasitic capacitance.

3. The method of claim 1, wherein the PCB integrated multi-winding planar transformer design method is characterized by, In the step S1, the trace structure of the winding is designed in series to increase the turns ratio or in parallel to increase the current carrying capacity.

4. The method of claim 1, wherein the PCB integrated multi-winding planar transformer design method is characterized by, In the step S1, the copper thickness of the PCB is selected according to the load current size, and 70μm thick copper is used for large current paths to reduce on-state impedance.

5. The method of designing a PCB integrated multi-winding planar transformer according to claim 1, wherein, In the step S2, the multi-layer symmetrical layout design is specifically a 6-layer board structure, and the layers are designed from top to bottom as follows: a part of the primary winding, an insulating dielectric layer, a first secondary winding layer, an internal ground shielding layer, a second secondary winding layer, and a part of the primary winding.

6. The method of designing a PCB integrated multi-winding planar transformer of claim 1, wherein, In the step S2, the thickness of the interlayer insulating dielectric layer is set to be less than or equal to 0.2mm.

7. The method of designing a PCB integrated multi-winding planar transformer of claim 1, wherein, In the step S3, before fixing the magnetic core, a heat-conducting insulating material with a heat conductivity greater than 3W / m·K is coated or padded on the contact area between the magnetic core and the PCB.

8. The method of designing a PCB integrated multi-winding planar transformer of claim 1, wherein, In the step S5, the parameter design of the heat-conducting via array is as follows: hole diameter 0.3mm and spacing 1.0mm.

9. The method of designing a PCB integrated multi-winding planar transformer of claim 1, wherein, In the step S1, the winding layout is optimized by a PCB design software to ensure the shortest current path and control the leakage inductance of the transformer to be below 1μH.

10. The method of designing a PCB integrated multi-winding planar transformer of claim 1, wherein, The working frequency range of the planar transformer is set to 100kHz to 500kHz.

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