WO2021091144A1

WO2021091144A1 - A connecting element for connecting a circuit board to a heat sink and method of establishing the connection

Info

Publication number: WO2021091144A1
Application number: PCT/KR2020/014690
Authority: WO
Inventors: Magnus Böh; Philipp Karutz; Stephan Werker; Vincent Wagener
Original assignee: Hanon Systems
Priority date: 2019-11-04
Filing date: 2020-10-27
Publication date: 2021-05-14
Also published as: DE102019129586A1

Abstract

The invention, which relates to a connecting element (1) for connecting a circuit board (2) to a heat sink (3) and a method for establishing the connection, is intended to solve the problem of identifying a simple and inexpensive solution for dissipating the heat generated in SMD components (11) on a circuit board (2). This problem is solved by this arrangement in that a plurality of through connections (4) are arranged in the circuit board (2), in that the connecting element (1) has a main body (7) comprising several sides and contact elements (8), whereby the plurality of contact elements (8) is arranged on a first side (5) of the main body (7), and in that the plurality of contact elements (8) of the connecting element (1) are placed on the plurality of through connections (4) of the circuit board (2). Fig. 3

Description

A CONNECTING ELEMENT FOR CONNECTING A CIRCUIT BOARD TO A HEAT SINK AND METHOD OF ESTABLISHING THE CONNECTION

The invention relates to a connecting element for connecting a circuit board to a heat sink.

The invention relates in particular to a thermally conductive connecting element for connecting a circuit board to a heat sink by means of which heat is dissipated from the circuit board to the heat sink.

The invention also relates to a process for establishing a connection between a circuit board and a heat sink by means of a connecting element.

Cooling components, especially components in the field of power electrics or power electronics, in order to avoid thermal damage to the components, for example, is already known.

It is common practice to connect the component to a heat sink, for example, to dissipate the heat generated in a component such as a power semiconductor switch. The heat sink increases the heat dissipating surface and thus dissipates the heat generated in the component.

Well-known power semiconductor switches are manufactured for this purpose, for example, in a so-called TO220 or TO247 housing, which has a metal surface for heat dissipation and can be fastened to a heat sink with a screw or rivet.

Such a heat sink is, for example, an arrangement consisting of a metal, such as aluminium, with several so-called fins to increase the heat-dissipation surface. Alternatively, a metallic housing can be used as a heat sink. For example, it is also possible to use the housing of a refrigerant compressor to dissipate the heat from a component. One or more components may be screwed or riveted to the housing, or a clamp fastening may be used to create a thermally conductive connection with the housing, for such purpose for example. Typically, parts of the housing are designed as flat surfaces for purposes of such a connection. Placing a thermally conductive material or a thermal interface material (TIM) between the housing and the component to provide electrical insulation is likewise typical. Another advantage of a thermally conductive material is that heat transfer resistance between the component and the housing is reduced or the thermal conductivity (thermal conduction coefficient) is improved.

This state of the art may be found, for example, in Infineon Technologies AG data sheet document reference number AN2017-42 for the TO-247-3 component entitled “TO-247-3 Advanced Isolation”, in particular on page 8, figure 9 and page 11, figure 12.

The use of components, such as power semiconductor switches, using a so-called through-hole technology (THT) and using components in type TO220 or TO247 housings leads to manufacturing costs that are higher than the manufacturing costs associated with the use components for surface-mounted devices (SMD).

The use of components for surface mounting, also known as SMD components, has another advantage, which is that the low-inductance designs of the SMD components allow higher switching frequencies for power semiconductor switches. Thus, for example, inverter modules or circuit boards suitable for controlling a motor may be made smaller, more powerful and less expensive.

Such SMD components, such as power semiconductor switches, are manufactured using materials such as SiC (silicon carbide) or GaN (gallium nitride) and are available in TO263 (D2PAK) housings.

A disadvantage of using such SMD components is that heat dissipation or cooling of the SMD components via their housing is no longer possible. For example, these SMD components cannot be mounted or screwed directly onto a heat sink, vehicle body parts or a housing.

Alternative methods of cooling of a circuit board equipped with SMD components in combination with a heat sink are not sufficiently possible due to the surface roughness of the circuit board, or a conductive coating on this circuit board, since the heat transfer resistance between such a circuit board and a connected heat sink is too high.

Accordingly, there is a need for improved heat dissipation for SMD components that are placed on a circuit board in order to enable the optimal functioning of such SMD components and to prevent thermally induced damage to the SMD components or to achieve a higher utilization of such components.

The purpose of the invention is to provide a simple and inexpensive solution for dissipating the heat generated in SMD components on a circuit board.

The problem is solved by the subject matter with the characteristics of patent claim 1 of the independent patent claims. Additional embodiments are described in the dependent patent claims.

The problem is also solved via a method having the characteristics of patent claim 8 of the independent patent claims. Additional embodiments are described in the dependent patent claims.

The solution is to place a thermally conductive, metallic connecting element between the circuit board equipped with SMD components and a heat sink or housing.

The circuit board has through connections into which contact elements of the connecting element may be press-fitted in order to create several thermally conductive connections between the circuit board and the connecting element, through which the heat generated by the SMD components can be dissipated. This enables heat dissipation from the SMD components via the circuit board, via the contact elements of the connecting element to a heat sink or a housing.

Such through connections or vias in the form of a vertical electrical connection between the track levels of a circuit board according to the state-of-the-art are known. In particular, the invention makes use of through connections that extend through the entire circuit board. However, using through connections that only extend to one of the inner layers of the multilayer circuit board is also possible.

For this purpose, the intent is to have a plurality of through connections arranged on the circuit board that are conventionally coated with an electrically conductive and heat conducting metal or alloy and connect at least two current-carrying layers with each other. In addition, a connecting element includes a main body comprising several sides and contact elements placed on a first side of the main body. These contact elements are press-fitted into the through connections of the circuit board and thus arranged within the through connections in such a manner.

Such through connections are very easy to create by means of a production process according to the state of the art. These through connections may also be produced in adjustable sizes, so that the dimensions of the through connections and contact elements can be modified.

Similarly, the intent is to have a circuit board comprising a multilayer board. It is possible to include electrically conductive and also heat-conductive structures in addition to the structures required for the functioning of the circuit board, especially when using such a multilayer circuit board. Such structures only serve to transport heat between the areas of the SMD components and the area of the through connections.

The main body is designed so that it is a cuboid, a cylinder or a prism with more than three corners. The contact elements place on one side of this main body are designed in the form of a prism with at least three corners. In particular, such a prism has three, four or six corners. Having the main body and the contact elements made of the same material is advantageous. Such a connecting element may be produced, for example, by milling, eroding or sawing the shapes of the contact elements from a metallic cuboid.

Contact elements are created which are each designed as a prism with four corners if, for example, milled sections in several rows and several columns are inserted into such a metallic cuboid. The dimensions of such contact elements may be in a range between 1 mm and 7 mm, preferably between 2 mm and 4 mm.

For example, if a main body is provided such that its contact elements are placed in this manner, they are arranged in an array comprising several rows and several columns on the main body.

The intent is to have the main body and the contact elements be made of metal. Metals such as copper or aluminium are preferably used for this purpose. The material for the main body and contact elements may be the same. A metal with good thermal conductivity or a good thermal conductivity coefficient should be selected given that heat is intended to be dissipated from the circuit board via the contact elements and the main body to a heat sink or housing. Copper with a thermal conductivity coefficient of 401 W/(m-K) (pure copper) and aluminium with a thermal conductivity coefficient of 236 W/(m-K) are commonly used on grounds of cost.

A heat sink is considered to be both a corresponding arrangement of one of the above metals and a housing, whereby such a housing may be a housing of an electric refrigerant compressor.

Coating the contact elements is likewise intended. The coating of contact elements may preferably comprise tin or a precious metal. Solderability is improved by coating the contact elements in this way and, in special cases, the application of a less noble metal is avoided.

The intent is likewise to have the main body placed with its second side on a heat sink or housing. This second side can be opposite the first side on which the contact elements are placed. In addition, a thermal interface material can be placed between the second side of the base body and the heat sink or housing. Such a thermal conducting material or a thermal interface material (TIM) improves heat conduction between the main body and the heat sink or housing and provides electrical insulation between the main body and the heat sink or housing.

According to present method, the intent is to have the circuit board include a plurality of coated through connections and to have the connecting element include a main body that has several contact elements on one of its sides. These contact elements are press-fitted into the plurality of through connections on the circuit board. In this context, the contact elements are inserted into the through connections creating a positive connection whereby the edges of the contact elements cut into the coating of the through connections and thus produce a thermally conductive connection or establish thermal connection points by creating cold welded joints between the through connections and the contact elements. Such cold welded joints have both good electrical conductivity characteristics and good thermal conductivity characteristics.

The contact elements are dimensioned in such a way that they have an assumed diameter or a diagonal that is chosen to be larger than the inner diameter of the through connections.

Accordingly, when the contact elements are press-fitted into the through connections, the edges of the contact elements cut at least partially into the coating located inside the through connections. Four edges cut into the coating of the through connections in a contact element comprising a prism with four corners. Thus, thermal joints are formed that have good thermal conductivity characteristics in four areas along the edges of the contact element within the through connections. Heat is transferred from the circuit board to the connecting element via these thermal connection points and from there to the heat sink or housing of an electric refrigerant compressor.

Coating the contact elements or the contact elements and the main body is also intended. Tin or a precious metal is preferably used for this purpose.

In addition, having the contact elements include a conical section at their ends facing away from the base body is also intended. This conical section makes it easier to press fit the contact elements into the through connections, for example by improving centring at the start of the press-fitting process.

Furthermore, an optional variant includes contact elements that are additionally soldered after being press-fitted into the through connections and the creation of cold welded joints. In this context having the contact elements coated with tin before being press-fitted is particularly advantageous. Soldering in this connection further improves thermal conductivity between the through connections and the contact elements.

In a further alternative, the contact elements may be inserted and soldered into the through connections without forming cold welded joints.

The invention thus enables efficient and effective heat dissipation without the use of additional heat sinks by using existing resources, for example the housing of an electric refrigerant compressor in a vehicle.

The freely definable sizes of the dimensions of the through connections and the contact elements, as well as the shapes of the contact elements, may be used to optimize the size of the thermal connection points at which the heat from the circuit board may be transferred via the through connections into the contact elements material and thus the connection element.

Further details, features and advantages of embodiments of the invention are set out in the following description of alternative embodiments with reference to the corresponding drawings. The figures show:

Fig. 1: an arrangement for cooling state-of-the-art power components;

Fig. 2: an enlarged representation of the surface of a state-of-the-art circuit board;

Fig. 3: a heat-conducting connecting element according to the invention by means of which heat is dissipated from the circuit board to the heat sink;

Fig. 4: a connection element according to the invention outfitted with 33 contact elements in three rows on a main body;

Fig. 5: the pressed-fitted position of a contact element within the corresponding through connection on a circuit board;

Fig. 6: a plurality of press-fitted contact elements in corresponding through connections on a circuit board.

Figure 1 shows an arrangement for cooling power components, such as a power semiconductor switch 10 according to the state-of-the-art. The power semiconductor switch 10 is connected by means of a through-hole mounting with its terminals connected to corresponding conductor tracks on the circuit board 2. Such power semiconductor switches 10, which for example have a TO220 or TO247 housing, are connected to a heat sink 3 for heat dissipation. These connections can be established by means of a screw or a rivet, for example.

A thermally conductive material 9 is arranged between the power semiconductor switch 10 and the heat sink 3 for purposes of electrical insulation and to improve heat conduction.

A direct connection between the SMD components 11 and a heat sink 3 is no longer possible when using SMD components 11 on a circuit board 2. Heat dissipation is therefore only possible via the circuit board 2 in the direction of a heat sink 3. This heat transfer is shown in Figure 3 by means of several arrows.

The surface roughness of the circuit board 2 is a hindrance when a circuit board 2 is directly connected to a heat sink 3. As shown in Figure 2 in an enlarged representation of the surface of a circuit board 2 according to the state-of-the-art, there are only a few direct contact points for heat transfer to heat sink 3. This disadvantage is independent of whether or not the surface of circuit board 2 is coated with an electrically conductive material that is also a thermally conductive material.

Figure 3 shows a heat-conducting connecting element 1 according to the invention by means of which heat is dissipated from the circuit board 2 to the heat sink 3. SMD components 11 are placed on one of the surfaces of the circuit board 2 the heat of which is to be dissipated in the direction of the heat sink 3.

As shown in the example in Figure 3, circuit board 2 has five through connections 4 in a row. These through connections 4 arranged in a row can be organised in several columns so as to create an array of through connections 4.

The heat-conducting connecting element 1 has a part of a main body 7 on which contact elements 8 are formed or placed. Five contact elements 8 are placed in a row in the example shown in Figure 3.

The contact elements 8 of connecting element 1 are press-fitted into the correspondingly arranged through connections 4. For this purpose, the dimensions of the through connections 4 and the contact elements 8 correspond to each other. This is independent of whether the contact element 8 is designed as a prism with 3, 4 or 6 corners, for example.

Designing the contact elements 8 as a prism with 4 corners is particular advantageous, as they are easy to produce and because they have edges with an angle of 90 degrees, which are able to easily cut into the coatings of the through connections 4 and thus form several thermal joints 12.

The connecting element 1 is connected to a second side 6, which may be opposite the first side 5, with a heat sink 3 in a manner that is heat conducting at a minimum. A thermally conductive material 9 can be placed between the connecting element 1 and the heat sink 3, such as a housing of a refrigerant compressor, to this end. This thermally conductive material 9 provides electrical insulation and improves heat dissipation in the direction of the heat sink 3.

An arrangement of, for example, eleven contact elements 8 in three rows on a main body 7 is shown in Figure 4. In this example, the contact elements 8 of the connecting element 1 are manufactured as prisms with a cross section comprising four corners, for example from a cuboid made of copper or aluminium. This connecting element 1 thus has 33 contact elements 8.

These 33 contact elements 8 are each press-fitted into one of 33 through connections 4 placed on the circuit board 2. It is clear that the through connections 4 on the circuit board 2 are likewise arranged in rows and columns so that each contact element 8 is press-fitted into an associated through connection 4.

The pressed-fitted position of a contact element within the corresponding through connection on a circuit board is shown in Figure 5. Four thermal joints 12 are created at the four 90-degree edges of the contact element 8 when press-fitting a contact element 8 that is designed as a prism with four corners.

Assuming that four contact elements 8 per row are arranged in three columns, 12 contact elements 8 on a main body 7 will thus create 48 thermal connection points 12, as shown as an example in Figure 6.

The large number of thermally conductive connections or thermal connection points 12 between the contact elements 8 of the connecting element 1 and the through connections 4 of the circuit board 2 leads to a reduction in heat transfer resistance and thus to improved heat dissipation of heat from the circuit board 1 in the direction of a heat sink 3, which may, for example, be the housing of an electric refrigerant compressor.

Reference numeral list

1 connecting element

2 circuit board

3 heat sink / housing

4 through connection

5 first side

6 second side

7 main body

8 contact elements

9 thermally conductive material / thermal interface material (TIM)

10 power semiconductor switches

11 SMD component

12 thermal connecting elements

Claims

A connecting element (1) for connecting a circuit board (2) to a heat sink (3), characterised in that a plurality of through connections (4) are arranged in the circuit board (2), in that the connecting element (1) has a main body (7) comprising several sides and contact elements (8), whereby the plurality of contact elements (8) is arranged on a first side (5) of the main body (7), and in that the plurality of contact elements (8) of the connecting element (1) are press-fitted into the plurality of through connections (4) of the circuit board (2).
A connecting element according to claim 1, characterised in that the main body (7) is a cuboid, a cylinder or a prism with at least three corners.
A connecting element according to claim 1 or 2, characterised in that the contact elements (8) in the form of a prism having at least three corners, in particular a prism having three, four or six corners, are placed on the first side (5) of the main body (7).
A connecting element according to any of claims 1 to 3, characterised in that the contact elements (8) are placed on the main body (7) in an array with a plurality of rows and several columns.
A connecting element according to any of claims 1 to 4, characterised in that the main body (7) and the contact elements (8) comprise a metal, preferably copper or aluminium.
A connecting element according to any of claims 1 to 5, characterised in that the contact elements (8) include a coating, preferably tin or a precious metal.
A connecting element according to any of claims 1 to 6, characterised in that the main body (7) is arranged with a second side (6) on a heat sink (3) or housing, whereby a thermal interface material (9) is placed between the main body (7) and the heat sink (3) or the housing.
A method for establishing a connection between a circuit board (2) and a heat sink (3) by means of a connecting element (1), characterised in that the circuit board (2) has a plurality of through connections (4), in that the connecting element (1) has a main body (7) with a plurality of contact elements (8), whereby the plurality of contact elements (8) have a first side (5) of the main body (7), in that the main body (7) is press-fitted into the plurality of through connections (4) of the circuit board (2) with its multiple contact elements (8) to establish the connection, whereby the contact elements (8) are joined positively in the through connections (4), and whereby the edges of the contact elements (8) cut into the coating material of the through connections (4) and thus produce a plurality of thermal connection points (12) by means of the creation of cold welded joints, and whereby the main body (7) is fastened with its second side (6) to the heat sink (3).
A method according to claim 8, characterised in that the main body (7) and the contact elements (8) comprise a metal, preferably copper or aluminium.
A method according to claim 8 or 9, characterised in that, at a minimum, the contact elements (8) have a coating, preferably of tin or a precious metal.
A method according to any of claims 8 to 10, characterised in that the contact elements (8) have a conical section at their ends facing away from the main body (7).