Method and printed circuit board for heat and current conduction in power electronic circuits

Abstract

Method for producing a heat and current conductor in power electronic circuits (202), in which a power electronic circuit is arranged on a printed circuit board (200, 500, 600, 700, 800), in which at least one metallic heat conductor tube (100, 400, 510, 710) is flattened at at least two locations (402, 502, 704), in which the at least two locations (402, 502, 704) are provided with a solderable surface, in which at least two metallic surfaces (206, 508), which are parts of conductor tracks, are provided on the printed circuit board (200, 500, 600, 700, 800), in which at least one metallic surface (206, 508) is located in the immediate vicinity of at least one power electronic component (202) of the power electronic circuit (202) arranged and electrically contacted with the at least one electronic component (202), wherein the at least one metallic heat conduction tube (100, 400, 510,710) at the at least two locations equipped with a solderable surface (302, 304, 306, 308, 402, 502, 704) are soldered to at least two provided metallic surfaces (206, 508) on the printed circuit board (200, 500, 600, 700, 800), wherein current transport via the at least one metallic heat conduction tube (100, 400, 510, 710) takes place at least between the at least two metallic surfaces (206, 508).

Description

[0001] The present invention relates to a method for producing a heat and current conductor in power electronic circuits. Additionally, a printed circuit board (PCB) produced by the method is claimed.

[0002] Unlike conventional power electronics with discrete, sometimes fist-sized components, such as thyristors or IGBTs with screw terminals and busbars, the latest power transistors are on the same scale as conventional ICs, thus allowing the integration of high-power circuits into typical circuit boards. However, such boards, with trace thicknesses of 35 micrometers, are unable to conduct high currents or absorb their heat. Modular power electronics circuits, such as those described in US publication US 9,496,799 B2, which decompose high electrical power into small, board-integrated power components and operate with low-voltage semiconductors, also require a way to conduct this power and current on circuit boards.

[0003] Furthermore, modern, fast-switching power semiconductors require very compact circuit implementations to achieve high speeds. A problem arises with spatially extensive circuit designs due to the parasitic inductances and the magnetic energy stored within them. These can discharge during switching operations and generate unwanted switching overvoltages that can damage or even destroy electronic components. Circuit boards comprising multiple layers of thick copper traces also suffer from this disadvantage, as components typically connected to the top and bottom layers, due to the large distance between them, significantly increase the area spanned by a current, and thus the parasitic magnetic inductances.

[0004] While thick copper traces are helpful for improving electrical and thermal conductivity, and electrical conductivity is relatively easy to achieve, possibly with additional metal inlays, high-current paths on the circuit board are often created using vertically arranged busbars, usually in through-hole mounting. However, thermal conductivity does not benefit from reinforced traces to the same extent as electrical conductivity and requires additional measures. Furthermore, metal inlays are expensive to manufacture and slow down the production process.

[0005] In the prior art, a so-called heat pipe, also known as a heat conduction tube, is therefore used specifically to promote heat conduction. For example, document US 2007 / 0195500 A1 describes the use of a flattened heat pipe for cooling an electronic component within a metallic housing. The heat pipe is connected to the component at one end and to a heat sink at the other.

[0006] US patent 2013 / 120937 A discloses a heat pipe that is soldered to a support structure but is in direct contact with the electronic component to be cooled. Both ends of the heat pipe are connected to a heat sink.

[0007] Document US 2017 / 0055372 A1 also describes a heat pipe running along a metal plate to dissipate heat from a component. In the area of ​​contact with the component, the heat pipe is flattened and soldered to the metal plate.

[0008] Document US 2007 / 0091577A1 describes an electronic device comprising a housing, a printed circuit board section, and a heat transfer element. The heat transfer element is positioned with its first end section in a heat absorption area and with its second end section in a heat dissipation area.

[0009] Document US 2017 / 0167799A1 discloses a heat pipe for cooling an electronic device. The heat pipe has a central section with a cavity filled with a heat transfer fluid.

[0010] Document US 9,192,043 B2 describes a device comprising a printed circuit board supported by posts and a heat pipe. The heat pipe is positioned with one end close to an electrical component located on the printed circuit board and with its other end close to one of the posts.

[0011] The publication EP 2 439 774 B1 shows a heat conduction tube with a flattened cross-section, which is provided with a nickel layer for better solderability.

[0012] Against this background, an object of the present invention is to provide a method for manufacturing a power electronic circuit in which both thermal and electrical conductivity on a printed circuit board are simultaneously increased. Standard manufacturing processes are to be used in order to benefit from fast and cost-effective industrial methods. Furthermore, an object of the present invention is to provide a printed circuit board manufactured using the method according to the invention.

[0013] To solve the aforementioned problem, a method for producing a heat and current conductor in power electronic circuits is provided, in which a power electronic circuit is arranged on a printed circuit board, in which at least one metallic heat conductor is flattened at at least two points, in which the at least two points are provided with a solderable surface, in which at least two metallic surfaces are provided on the printed circuit board, in which at least one metallic surface of the at least two metallic surfaces is arranged in the immediate vicinity of at least one power electronic component of the power electronic circuit and is electrically contacted with the at least one electronic component.wherein the at least one metallic heat conductor tube is soldered to the at least two provided metallic surfaces on the circuit board at the at least two locations equipped with a solderable surface.

[0014] The printed circuit board (PCB) is manufactured using a standard process with a conductor thickness of 35 or 70 micrometers. The power electronic components are shaped similarly to a chip package and are arranged on the PCB and connected via the conductors. Both surfaces of the PCB can be plated through using conventional technologies, such as vias. Metal traces within the PCB are also possible.

[0015] The at least two metallic surfaces to be provided on the circuit board can be parts of conductive traces. To ensure good heat transfer to a heat pipe contacted with these surfaces, the metallic surfaces can be structured, for example, with vias. This allows for targeted heat dissipation via a heat pipe, which is also contacted with the at least two metallic surfaces precisely at those points where additional current transport is required. Current transport thus takes place via the heat pipe at least between the at least two metallic surfaces, while heat, for example, is dissipated.from a power electronic component in the vicinity, wherein the power electronic component is electrically contacted with at least one of the at least two metallic surfaces, to another of the at least two metallic surfaces and / or to a heat sink via the heat conduction tube.

[0016] The at least one heat pipe, also known as a heat tube by those skilled in the art, is made of electrically conductive materials, preferably aluminum or copper due to their high electrical and electrothermal conductivity. Brass is also a possible alternative. To facilitate soldering to the largely flat printed circuit board or to conductor tracks on the printed circuit board at the at least two provided metallic surfaces, the heat pipe is flattened at the at least two points intended for soldering. To further enhance solderability of these at least two flattened areas, metals particularly suitable for bonding with solder can be applied to them, for example, by vapor deposition. These metals include, for example, copper or brass, preferably nickel or tin. Such a point, in particular each of the at least two points, of the heat pipe can be, for example,It consists of a flattened section of the heat pipe wall made of aluminum at least 0.2 mm thick, which is coated with nickel at least 1 micrometer thick and then with tin 10 micrometers thick. The coating can be applied chemically and / or electroplated.

[0017] Each solder joint preferably represents a planar solder connection between one of the at least two locations on the underside of the heat pipe and one of the at least two metallic surfaces on the printed circuit board, which may be a conductor pad and / or optionally part of a conductor track. Such a metallic surface on the printed circuit board must be contactable by solder, i.e., it should be free of solder mask and / or surface-treated with antioxidants.

[0018] A soldering technique is selected from the state of the art. It can be implemented, for example, using reflow or vapor phase soldering. In this process, the conductor pads of the metallic areas on the printed circuit board (PCB) that are to be contacted by the at least one heat pipe are coated with solder. The at least one heat pipe is then positioned on these pads, with its at least two points aligned with the at least two metallic areas on the PCB. If necessary, the heat pipe is fixed to the PCB with adhesive. Finally, the entire PCB, including the heat pipe, is heated in an oven to melt the solder paste. Simultaneously, other components, such as components of the power electronic circuit, can be positioned on the PCB, optionally coated with solder paste.

[0019] The heat-conducting tube has, for example, a wall thickness of at least 0.2 mm, preferably at least 0.5 mm, made of an electrically conductive material, such as aluminum or copper. Such thicknesses are necessary to enhance the desired effect of improved heat and current conduction compared to the conductor tracks on the printed circuit board, which typically have a cross-sectional area of ​​35 micrometers or 70 micrometers, or optionally even 105 to 150 micrometers. The inventive method makes it possible to lithographically structure the conductor tracks of the printed circuit board with high resolution using standard manufacturing processes. This allows for fine contact spacing for typical SMD components (surface-mounted devices) without the risk of short circuits, while still achieving a current path with an increased electrical cross-section.At the same time, the current paths, i.e. the combination of conductor track and heat pipe or heat pipe alone, have increased thermal conductivity and no longer have the problem from the prior art that a thicker conductor track does not increase thermal conductivity to the same extent as electrical conductivity.

[0020] The inventive method can be integrated into a standard manufacturing process, unlike the complex inlay manufacturing process.

[0021] In one embodiment of the method according to the invention, the at least one heat pipe is designed to be completely flat. Generally, the at least one heat pipe can extend beyond the circuit board in order to transfer heat to a heat sink, e.g., a heat sink.

[0022] In a further embodiment of the method according to the invention, the at least two solderable points of the heat conductor tube are provided with holes and / or grooves with a round, conical, or angular profile. Such surface structuring advantageously improves thermal contact, i.e., heat transfer across the respective contact point. Particularly in large-area soldering of flat areas of the heat conductor tube and metallic surfaces of the printed circuit board, inclusions of solvent and / or flux or their outgassing can form, which impede heat transfer. Such inclusions are avoided by the surface structuring of the respective at least two points of the heat conductor tube provided in the embodiment of the method according to the invention, since the aforementioned undesirable solder components can escape, for example, through the grooves or accumulate, for example, in the holes.Thus, the effective contact area available for heat transfer, formed by one of the at least two points on the heat pipe and one of the metallic surfaces on the printed circuit board (PCB), is not reduced by soldering between the PCB and the heat pipe. The surface structuring of the two flat points on the heat pipe can be achieved, for example, by milling, etching, and / or embossing. Similarly, a dense grid can be created on the surface of the two metallic surfaces on the PCB using vias. Advantageously, each of these vias has a diameter of less than 0.4 mm. Such a hole can be mechanically drilled or laser-cut, and can be through-hole or blind, for example, tapered conically.

[0023] In a further embodiment of the method according to the invention, the at least one heat conduction tube is coated at at least one point with an electrically insulating material, e.g. solder mask, to prevent electrical contact between the at least one heat conduction tube and conductor tracks of the circuit board.

[0024] In a further embodiment of the method according to the invention, the printed circuit board is coated with an electrically insulating material at at least one location which is covered by the at least one heat pipe, in order to avoid electrical contact between conductor tracks of the printed circuit board and the at least one heat pipe before the at least one heat pipe is mounted.

[0025] The at least one heat pipe and / or the printed circuit board can be partially insulated. The two embodiments of the method according to the invention mentioned above enable the crossing of conductor paths by having the attached heat pipe transport the current on a kind of additional conductor layer, independent of existing layers of the printed circuit board. The electrically insulating material ensures that conductor tracks or pads of the printed circuit board covered by the heat pipe do not contribute to the current flow in the heat pipe.

[0026] In a further embodiment of the method according to the invention, the printed circuit board is coated with a thermally conductive material at at least one location covered by the heat pipe before the heat pipe is mounted, thus facilitating heat transfer between the printed circuit board and the at least one heat pipe. This allows additional heat to be dissipated from areas on the printed circuit board covered by the at least one heat pipe.

[0027] In a further embodiment of the method according to the invention, the power electronic circuit is formed by at least one module of a modular multilevel converter.

[0028] Furthermore, a printed circuit board is claimed for use as a heat and current conductor in power electronic circuits, which comprises a power electronic circuit arranged on it, which additionally comprises at least one metallic heat conductor tube which is flattened at at least two points and is designed to be soldered at these at least two points, wherein the printed circuit board has at least two metallic surfaces, wherein at least one metallic surface is arranged in the immediate vicinity of at least one power electronic component of the power electronic circuit and is electrically contacted with it, wherein the at least one metallic heat conductor tube is soldered to the at least two metallic surfaces provided on the printed circuit board at its at least two solderable points.

[0029] In an embodiment of the printed circuit board according to the invention, the printed circuit board has a thermally conductive but electrically insulating material on at least one surface covered by the at least one heat conduction tube.

[0030] In a further embodiment of the printed circuit board according to the invention, the power electronic circuit comprises at least one module of a modular multilevel converter.

[0031] Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

[0032] It is understood that the features mentioned above and those to be explained below can be used not only in the combinations specified, but also in other combinations or on their own, without leaving the scope of the present invention.

[0033] The figures are described in a coherent and comprehensive manner; identical components are assigned the same reference symbols. Fig. Figure 1 shows a heat conduction tube used in an embodiment of the method according to the invention. Fig. Figure 2 shows a contacting process of a heat pipe on a printed circuit board in one embodiment of the method according to the invention. Fig. Figure 3 shows examples of surface structuring carried out on a flat area of ​​the heat conduction tube in an embodiment of the method according to the invention. Fig. Figure 4 shows a heat-conducting tube with partial paint insulation used in an embodiment of the method according to the invention. Fig. Figure 5 shows a contacting process of a partially electrically insulated heat pipe on a printed circuit board in one embodiment of the method according to the invention. Fig. Figure 6 shows a contacting process of a partially electrically insulated heat pipe on a circuit board with additional heat transfer to the heat pipe, carried out in an embodiment of the method according to the invention. Fig. Figure 7 shows a contacting process of a heat pipe equipped with a gap pad on a printed circuit board in an embodiment of the method according to the invention. Fig. Figure 8 shows a contacting process of a partially insulated heat pipe on a printed circuit board with additional heat transfer to the heat pipe, carried out in an embodiment of the method according to the invention.

[0034] In Fig. Figure 1 shows a heat conduction tube 100 used in an embodiment of the method according to the invention. The heat conduction tube 100 is flat along its entire longitudinal extent.

[0035] In Fig. Figure 2 shows a contacting process of a heat pipe 100 on a printed circuit board 200 in one embodiment of the method according to the invention. Eight SMD power semiconductors 202 are arranged on the printed circuit board 200, which are in contact with conductor tracks 204 located under a solder mask and, for example, represent a module of a modular multilevel converter. The heat pipe 100 is to be contacted with the circuit board 200 in the center of the printed circuit board, between each group of four SMD conductor tracks, and, for example, soldered to the conductor pads 206 arranged there.

[0036] In Fig. Figure 3 shows four examples 302, 304, 306, 308 of surface structurings 300 applied to a flat area of ​​the at least two points of the heat conductor tube to be soldered to the printed circuit board in an embodiment of the method according to the invention. Grooves 302, 304, 306 are particularly advantageous due to their comparatively effective solvent wicking. They can be manufactured, for example, by embossing or roll embossing, which is carried out prior to coating with nickel and tin or titanium and tin. The depth of the respective surface structures should be less than half, advantageously less than one-third, or even less than 100 micrometers, of the wall thickness of the heat conductor tube, where the wall is the material remaining in the area of ​​the structuring. Holes 308 are recesses with a round, conical, or angular profile and are generally created by drilling.

[0037] In Fig. Figure 4 shows a heat conduction tube 400 with partial lacquer insulation 404 used in an embodiment of the method according to the invention. Only at two areas 402, which here represent the at least two points to be soldered to the printed circuit board, is the bare material of the heat conduction tube exposed for electrical contact. The partial lacquer insulation 404 can be achieved, for example, at operating voltages on the printed circuit board around 200 V by multiple coatings of insulating polymer, e.g., polyimides, polyamides, polyesterimides, polyamideimides, or polyurethanes. If higher operating voltages occur, a polyimide film or aramid foil is preferably used. Alternatively, a powder coating can also be used.

[0038] In Fig. Figure 5 shows a contacting process, carried out in one embodiment of the method according to the invention, of a partially electrically insulated heat pipe 510 on a printed circuit board 500 at the metallic surfaces 508. As indicated by the two curved arrows, the two points 502 of the heat pipe are positioned on the two metallic surfaces 508 of the printed circuit board 500 and soldered to them. The heat pipe 510 is coated with an insulating material at two points 512. Due to the insulation, when the heat pipe 510 is positioned according to the arrows, no electrical contact is possible with the conductor tracks on the printed circuit board 500 covered by the heat pipe 510. This means that the conductor track 506 is electrically bridged by the insulating coating or varnish 512 of the heat pipe 510.

[0039] In Fig. Figure 6 shows a contacting process carried out in an embodiment of the method according to the invention, involving a partially electrically insulated heat-conducting tube 400 on a printed circuit board 600 with additional heat transfer 602 to the heat-conducting tube 400. The heat-conducting tube 400 is a heat-conducting tube 400 that is not covered by an insulating material at two points 402. Fig. 4. The two points 402 of the heat pipe are soldered to the pads 508 of the circuit board 600, as indicated by the respective arrows. A thermal paste 602, additionally applied to one of the conductor tracks—namely, to the circuit board 506 located beneath the heat pipe 400 when it is positioned on the circuit board 500—ensures heat transfer from the underlying conductor track 506 to the heat pipe 400. The thermal paste 602, e.g., a thermally conductive adhesive, is thermally conductive but not electrically conductive.

[0040] In Fig. Figure 7 shows a contacting process carried out in one embodiment of the method according to the invention, involving a heat pipe 710 equipped with a gap pad 702 on a printed circuit board 700. The gap pad 702, which is preferably adhesive on both sides, is thermally conductive but not electrically conductive, so that after soldering the heat pipe 710 to the printed circuit board 700, i.e., the two points 704 of the heat pipe 710 to the two metallic surfaces or pads 508, no current transfer from the underlying conductor track 506 to the heat pipe 710 can take place. This means that the conductor track 506 is thermally but not electrically connected. The conductor track 506 does not necessarily have to have a solder mask here, but can be bare. A material is preferably selected for the gap pad 702 which acts as an electrical insulator up to a required voltage level.The Gap-Pad 702 can extend on each side by at least the lengths specified as creepage distances for the operating voltages according to IEC 60664.

[0041] In Fig.Figure 8 shows a contacting process, carried out in one embodiment of the method according to the invention, of a partially insulating-coated heat pipe 510 on a printed circuit board 800 with additional heat transfer to the heat pipe 510 via a gap pad 802. While the insulating material 512 on the heat pipe 510, after positioning and contacting / soldering of the heat pipe 510 on the printed circuit board 800, provides electrical insulation against further current transfer from conductor tracks of the printed circuit board 800 covered by the heat pipe 510, as indicated by the curved arrows, the gap pad 802 enables heat transfer from the conductor track 506 covered by the heat pipe 510 to the heat pipe 510. The conductor track 506 is electrically bridged by the insulating coating or varnish 512 of the heat pipe 510.

Claims

[1] Method for producing a heat and current conductor in power electronic circuits (202), in which a power electronic circuit is arranged on a printed circuit board (200, 500, 600, 700, 800), in which at least one metallic heat conductor (100, 400, 510, 710) is flattened at at least two locations (402, 502, 704), in which the at least two locations (402, 502, 704) are provided with a solderable surface, in which at least two metallic surfaces (206, 508) which are parts of conductor tracks are provided on the printed circuit board (200, 500, 600, 700, 800), in which at least one metallic surface (206, 508) is located in the immediate vicinity of at least one power electronic component (202) of the power electronic circuit (202) arranged and electrically contacted with the at least one electronic component (202), wherein the at least one metallic heat conduction tube (100, 400, 510,710) at the at least two locations equipped with a solderable surface (302, 304, 306, 308, 402, 502, 704) are soldered to at least two provided metallic surfaces (206, 508) on the printed circuit board (200, 500, 600, 700, 800), wherein current transport via the at least one metallic heat conduction tube (100, 400, 510, 710) takes place at least between the at least two metallic surfaces (206, 508). [2] Method according to claim 1, wherein the at least one heat conduction tube (100, 400, 510, 710) is designed to be flat throughout. [3] Method according to one of the preceding claims, wherein the at least one solderable location (302, 304, 306, 308) is provided with holes and / or grooves having a round, conical or angular profile. [4] Method according to one of the preceding claims, wherein the at least one heat conduction tube (100, 400, 510, 710) is coated at least at one point with an electrically insulating material (404, 512, 702) to prevent electrical contact between the at least one heat conduction tube (100, 400, 510, 710) and conductor tracks (506) of the printed circuit board (200, 500, 600, 700, 800). [5] Method according to one of the preceding claims, wherein the printed circuit board (200, 500, 600, 700, 800) is coated with an electrically insulating material (602, 802) at at least one location which is covered by the at least one heat guide tube (100, 400, 510, 710) to prevent electrical contact between conductor tracks (506) of the printed circuit board (200, 500, 600, 700, 800) and the at least one heat guide tube (100, 400, 510, 710) prior to mounting the at least one heat guide tube (100, 400, 510, 710). [6] Method according to one of the preceding claims, wherein the printed circuit board (200, 500, 600, 700, 800) is coated with a thermally conductive material (602, 802) at at least one location which is covered by the heat guide tube (100, 400, 510, 710) to facilitate heat transfer between the printed circuit board (200, 500, 600, 700, 800) and the at least one heat guide tube (100, 400, 510, 710) prior to mounting the at least one heat guide tube (100, 400, 510, 710). [7] Method according to one of the preceding claims, wherein the power electronic circuit (202) is formed by at least one module (202) of a modular multilevel converter. [8] Printed circuit board (200, 500, 600, 700, 800) for a heat and current conductor in power electronic circuits (202), which comprises a power electronic circuit (202) arranged on it, which additionally comprises at least one metallic heat conductor tube (100, 400, 510, 710) which is flattened at at least two points (402, 502, 704) and is designed to be solderable at at least two points (402, 502, 704), wherein the printed circuit board (200, 500, 600, 700, 800) has at least two metallic surfaces (206, 508) which are parts of conductor tracks, wherein at least one metallic surface (206, 508) is in the immediate vicinity of at least one power electronic component (202) of the power electronic circuit (202) is arranged and electrically contacted with it, wherein the at least one metallic heat conduction tube (100, 400, 510, 710) is connected at its at least two solderable locations (302, 304, 306, 308, 402, 502,704) is soldered to the at least two metallic surfaces (206, 508) provided on the circuit board (200, 500, 600, 700, 800), wherein the at least one metallic heat conduction tube (100, 400, 510, 710) is configured to transport current at least between the at least two metallic surfaces (206, 508). [9] Printed circuit board (200, 500, 600, 700, 800) according to claim 8, which has a thermally conductive but electrically insulating material (404, 512, 602, 702, 802) on at least one surface covered by the at least one heat guide tube (100, 400, 510, 710). [10] Printed circuit board (200, 500, 600, 700, 800) according to claim 8 or 9, wherein the power electronic circuit (202) comprises at least one module (202) of a modular multilevel converter.

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