DE102006001188A1 - Arrangement for cooling power components on printed circuit boards and method for producing the same - Google Patents

Abstract

The invention relates to an arrangement for cooling at least one component, in particular at least one power component, the at least one component being attached to a circuit board which is provided on at least one side with a layer of an electrically conductive material. DOLLAR A It is provided that an inner surface (13) of the electrically conductive material is formed by at least one recess (12) in the circuit board (3), on the inner surface (13) at least one component is arranged, and on the inner surface ( 13) opposite outer surface (21) a heat sink (1) is arranged. DOLLAR A The invention also relates to a method for producing an arrangement for cooling power components on circuit boards, in particular of the type mentioned above.

Description

The The invention relates to an arrangement for cooling at least one Component, in particular a power component, with the in the preamble of claim 1 features.

Further The invention relates to a method for producing an assembly for cooling of power components on printed circuit boards of the type mentioned above.

was standing of the technique

It is known that of power devices such as semiconductor switches, Capacitors or inductors generated heat of power converters (for example bridge circuits of electric motors, DC-DC converters to power computers and the like a.), the on a printed circuit board made of epoxy resin with an upper copper layer soldered are about so-called thermal vias of the power components by the Printed circuit board on the back respectively, where they are then over an electrically insulating film is passed onto a heat sink. Thermal Vias are thereby vias of the circuit board under the mounting surface the power components.

however is in this structure for deriving the power loss of the power devices the thermal resistance between a housing bottom of a Power component and the heatsink forming a heat sink relative high. The greatest thermal resistance has in this structure, an electrically insulating film, the required for electrical insulation of the power device from the heat sink is. As the thermal vias eg. As a grid-shaped holes arranged are formed, there is no full-surface contact between the caseback a power device and the copper layer of the circuit board, soldered on this are, as well as a lower copper layer and the electrically insulating Foil.

For example, a typical device, for example, a transistor whose mounting plate has a base area of about 20 mm ² , a maximum thermal resistance between the junction (junction of the transistor) - housing bottom of about 1.2 K / W on. The other thermal resistances to the heat sink in a prior art arrangement are: 1. Lot: Caseback - upper copper layer 0.09 K / W 2. Thermal vias 0.50 K / W 3. foil (3.5 W / m · K, 0.2 mm) 1.90 K / W Sum (housing bottom - heat sink) 2.49 K / W Junction - caseback 1.20 K / W Sum (junction - heat sink) 3.69 K / W

Consequently is the total thermal resistance in this type of connection more than three times as high as the thermal resistance between junction caseback.

advantages the invention

The inventive arrangement with the features mentioned in claim 1 offers the other hand Advantage that the heat resistance stood between the junction of a semiconductor device and a heat sink more than 60% can be reduced. In that by at least a recess in the printed circuit board an inner surface of the electrically conductive material is formed on the inner surface at least one component is arranged, and on the outer surface opposite to the inner surface Heat sink arranged is, a device is only through a lower layer of conductive material at the bottom of the PCB separated from the heat sink. It can the Heat sink made of aluminum or a suitable aluminum alloy. Alternatively, you can also a heat sink find another material use.

In a preferred embodiment The invention provides that the heat sink and / or the layer of electrically conductive Material on the heat sink facing Side has an electrically insulating protective layer. It can the protective layer of an anodized on the heat sink Aluminum oxide may be formed when the heat sink made of aluminum or a Aluminum alloy exists.

In a further embodiment it is envisaged that the protective layer on the heat sink and / or on the bottom the layer of electrically conductive material and / or an electrically not conductive paint, especially baked enamel exists.

It is preferably provided that between the protective layer and the lower layer of an electrically conductive material, a heat conducting layer is provided. This heat-conducting layer ensures full-surface thermal contact without disturbing air films and compensates for unevenness and roughness out. The heat conducting layer may be formed of a thermal paste and have a thickness of 10 to 100 microns. Alternatively, baked enamel can be used, in which case the protective layer can be dispensed with, in particular if only small demands are placed on the electrical insulation. In this case, the use of heat sinks, which are made of materials other than aluminum or aluminum alloys into consideration.

It is further provided that the heat conducting layer of a thermal paste and / or a good thermal conductivity adhesive is formed

Further is preferably provided that the circuit board formed of epoxy resin is the glass fiber reinforced can be and the conductive one Material contains copper. In this case, the layer of conductive material preferably has a thickness of 30 to 120 μm, in particular a thickness of 100 to 110 microns on.

Further is preferably provided that the circuit board on both sides with a Layer is provided of an electrically conductive material, so that both on the top and on the bottom of a layer made of electrically conductive Material is provided, according to their structuring of the electrical contact of components can serve. there is provided in a preferred embodiment of the invention, that both layers have substantially the same thickness, which improves the mechanical and thermal properties.

Prefers is provided that the at least one recess by milling or Punching is made, resulting in cost-effective and automated batch production allowed.

It is further preferably provided that between the upper electrically conductive Layer and the lower electrically conductive layer more electrically conductive Layers are arranged as wiring levels of components (Mulitlayer).

• – Strukturieren einer oberen Schicht einer Leiterplatte,
• – Herstellen von wenigstens einer Ausnehmung,
• – Aufbringen einer unteren Schicht,
• – Bestücken der Leiterplatte mit wenigstens einem Bauelement, und
• – Verbinden der Leiterplatte mit einem Kühlkörper.

Furthermore, the invention relates to a method for producing an arrangement for cooling components on printed circuit boards, in particular of the type described above, with the steps:

• Structuring an upper layer of a printed circuit board,
• Producing at least one recess,
• Application of a lower layer,
• - Equipping the circuit board with at least one component, and
• - Connect the circuit board with a heat sink.

With This method, the arrangement described above, inexpensive and be produced automatically. Furthermore, in addition, a heat conducting layer be applied, which improves the thermal connection.

drawings

The Invention will be described below in an embodiment with reference to the accompanying drawings explained in more detail. It demonstrate:

1 a section along the line AA in 8th by an embodiment of the inventive arrangement;

2 an enlarged section of the 1 ;

3 an upper surface of a one-side copper-coated circuit board, wherein a top layer is patterned;

4 the circuit board of 3 after a further process step, wherein recesses are formed for power devices;

5 shows the underside of a printed circuit board on which a second layer of copper has been applied;

6 shows the top of the circuit board after applying and structuring the second layer;

7 shows another process step in which vias are made from the upper to the lower copper layer; and

8th shows a board equipped with components.

description the embodiments

1 and 2 show a heat sink 1 , For example. Of aluminum or an aluminum alloy, at its contact surface 2 with a circuit board 3 connected is.

Here is the contact surface 2 with a protective layer 4 provided, for example, is formed from an anodized aluminum oxide. Further, between the contact surface 2 and the circuit board 3 a heat conducting layer 5 provided, for example, has a thickness of 10 to 100 microns and may be formed from a thermal paste or a thin electrically insulating lacquer layer, for example. A baked enamel.

The circuit board 3 is, for example, made of epoxy resin 6 formed and has at its top 7 an upper layer 9 and at their bottom 8th a lower one layer 10 made of an electrically conductive material, such as. Copper on. The thickness of the layers 9 . 10 on the top and bottom 7 . 8th is about 30-120 microns.

In the in the 1 and 2 illustrated embodiment are along the section along the line AA in 8th on the top 7 two capacitors 11 arranged. Furthermore, the circuit board 2 two recesses 12 in whose area the epoxy resin 6 and the upper layer 9 are removed such that at the lower layer 10 on the bottom 8th an inner surface 13 is formed. On this inner surface 13 are each a transistor 14 arranged so that the transistors 14 only through the lower layer 10 and through the heat conducting layer 5 from the protective layer 4 of the heat sink 1 are separated, at one to the inner surface 13 opposite outer surface 21 is arranged.

The transistors 14 each include a transistor chip 15 that by means of a carrier 16 on the lower layer 10 on the inner surface 13 is attached. For electrical contacting is a bonding wire 17 to a connection 22 guided, which makes an electrical connection with the inner surface 13 manufactures.

It will now be based on the 3 to 8th a method for producing an arrangement according to the invention explained, here for example. Based on a 3-phase motor bridge.

The starting point is a circuit board 3 made of epoxy resin with a single-sided coating of copper on top 7 as upper layer 9 on the circuit board 3 is applied.

In a first step (see 3 ) becomes the upper layer 9 the circuit board 3 structured. This can be done by means of customary photographic transmission techniques and etching methods.

In a second step (see 4 ) will be recesses 12 formed at the points where transistors 14 , such as power transistors, are to be arranged. This is the epoxy resin 6 eg completely removed by punching.

In a third step (see 5 ) will be on the bottom 8th The printed circuit board is applied to an approximately 105 micron thick layer of an electrically conductive material, such as copper, which is a lower layer 10 forms. In this case, the lower layer forms 10 the outer surface 21 on which a heat sink 1 For example, can be added by pressing and the outer surface 21 opposite inner surface 13 , on the example of transistors 14 can be fixed by means of soldering. Furthermore, holes 18 introduced as the connec se for components such as capacitors 11 or transistors 14 serve. In addition, positive supply connections 23 , negative supply connections 24 and motor winding connections 25 educated. 6 shows the top 7 with the upper layer 9 as well as recesses 12 of the epoxy support material. In the recesses 12 is the inner surface 13 the lower layer 10 visible, noticeable.

In a fourth step (see 7 ) become vias 19 made, for example, connections between the top 7 and the bottom 8th produce.

In a fifth and final step (see 8th ) becomes the circuit board 2 stocked. In the present embodiment, six power transistors 14 on the inner surface 13 one recess each 12 soldered and five parallel capacitors 11 intended. Furthermore, here is in the lower layer 10 a shunt resistor 20 intended for current measurement, which like the power transistors 14 thermally close to a heat sink 1 is connected and two jumper wires 27 ,

The ready assembled circuit board 2 comes with a heat sink 1 , For example by means of a leaf spring, which on the top of the power transistors 14 presses, connected (not shown). The pressure of the leaf spring ensures good thermal contact of the underside 10 with the heat sink 1 and allows a small layer thickness of the thermal compound. The leaf spring is with the heat sink 1 firmly connected, for example by means of a clip connection.

The thermal resistances achievable with this method are: 1. Lot: Caseback - lower copper layer 0.08 K / W 2. Copper conductor track (400 W / m · K, 0.1 mm) 0.012 K / W 3. Thermal compound (2 W / m · K, 0.01 mm) 0.067 K / W 4. Anodized layer (30 W / m · K, 0.03 mm) 0.033 K / W Sum (housing bottom - heat sink) 0.192 K / W

Junction - caseback 1.20 K / W total (Junction - heat sink)  1,392 K / W

In order to is the total thermal resistance between the junction of the power transistors and the heat sink in the inventive arrangement reduced by more than 60%.

It should be noted that the Wärmewider Case bottom - Junction is specific to the device, and due to the structure of the semiconductor device is conditioned (for example, with power transistors in DPack housing about 1.2 K / W).

The assembly-related additional thermal resistance is according to a known from the prior art arrangement, consisting of thermal vias and insulation film 2.49 K / W, however, according to the invention 0.192 K / WDh, the thermal resistance caused by the installation is increased by a factor of about 13 reduced. For a shunt resistor, which is part of the lower copper layer and has a resistance area of 13 mm ² , results according to the prior art, a value for the thermal resistance of 4.4 K / W, while this according to the invention to 0.46 K. / W, wherein the proportion of the thermal resistance resulting from the thermal grease is 0.38 K / W and the proportion of the anodized layer is 0.08 K / W. This results in a reduction of the installation-related thermal resistance of the shunt resistor by a factor of 9.6.

Claims (14)

Arrangement for cooling at least one component, in particular at least one power component, wherein the at least one component is mounted on a printed circuit board, which is provided on at least one side with a layer of an electrically conductive material, characterized in that at least one recess ( 12 ) in the printed circuit board ( 3 ) an inner surface ( 13 ) of the electrically conductive material is formed on the inner surface ( 13 ) at least one component is arranged, and on the inner surface ( 13 ) opposite outer surface ( 21 ) a heat sink ( 1 ) is arranged. Arrangement according to claim 1, characterized in that the heat sink ( 1 ) and / or the layer ( 10 ) made of electrically conductive material on the heat sink ( 1 ) facing side an electrically insulating protective layer ( 4 ) having. Arrangement according to claim 2, characterized in that the protective layer ( 4 ) on the heat sink ( 1 ) is an anodized aluminum oxide layer. Arrangement according to claim 2, characterized in that the protective layer ( 4 ) on the heat sink ( 1 ) and / or on the underside of the layer ( 10 ) consists of electrically conductive material of an electrically non-conductive paint, especially baked enamel. Arrangement according to claim 2, 3 or 4, characterized in that between the protective layer ( 4 ) and the layer ( 10 ) of an electrically conductive material, a heat conducting layer ( 5 ) is provided. Arrangement according to claim 5, characterized in that the heat conducting layer ( 5 ) is formed from a thermal paste and / or a good thermal conductivity adhesive. Arrangement according to one of the preceding claims, characterized in that the printed circuit board ( 3 ) made of epoxy resin ( 6 ) is formed and the conductive material contains copper. Arrangement according to one of the preceding claims, characterized in that the layer ( 10 ) has a thickness of 30 to 120 microns, in particular a thickness of 100 to 110 microns. Arrangement according to one of the preceding claims, characterized in that the printed circuit board ( 3 ) on both sides with one layer each ( 9 . 10 ) is provided of an electrically conductive material. Arrangement according to claim 9, characterized in that both layers ( 9 . 10 ) have substantially the same thickness. Arrangement according to one of the preceding claims, characterized in that the at least one recess ( 12 ) is made by milling or punching. Arrangement according to one of the preceding claims, characterized in that between the upper electrically conductive layer ( 9 ) and the lower electrically conductive layer ( 10 ) Further electrically conductive layers are arranged as wiring levels of components (multilayer). Arrangement according to one of the preceding claims, characterized in that the at least one component ( 14 ), which on the inner surface ( 13 ) of the conductive layer ( 10 ) is arranged and / or the circuit board ( 3 ) by mechanical means, such as a spring on the outer surface ( 21 ) of the heat sink ( 1 ) is pressed. Method for producing an arrangement for cooling components on printed circuit boards, in particular for producing an arrangement according to one of the preceding claims, comprising the steps of: - structuring an upper layer ( 10 ) of a printed circuit board ( 3 ), - producing at least one recess ( 12 ), - applying a lower layer ( 9 ), - equipping the printed circuit board ( 3 ) with at least one component, and - connecting the circuit board ( 3 ) with a heat sink ( 1 ).