EP4196314A1

EP4196314A1 - Method and device for the temperature-critical joining of two component layers

Info

Publication number: EP4196314A1
Application number: EP21749631.4A
Authority: EP
Inventors: Christoph BANTEL; Emilia SCHWINDT; Nathanael Eisenreich
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2020-08-12
Filing date: 2021-07-27
Publication date: 2023-06-21
Also published as: WO2022033869A1; DE102020210201A1; CN116157226A

Abstract

The invention presented relates to a method (100) for the temperature-critical joining of a first electrically conductive component layer (103, 301) having a first constant material thickness and a second component layer (105, 303) having a second constant material thickness, there being disposed on the second component layer (105, 303) at least one electronic component which has a critical temperature below a melting point of the first component layer (103, 301) and of the second component layer (105, 303). The method (100) comprises the following steps: - arranging the first component layer (103, 301) over the second component layer (105, 303) without a gap; - moving a laser beam (101) with constant power along the first component layer (103, 301) with a welding advancement which causes a material forming the first component layer (103, 301) to be partly melted down to the second component layer (105, 303) by means of energy input of the laser beam (101) and which causes only material in a surface region (111, 307) of the second component layer (105, 303) to be melted by means of the energy input.

Description

description

title

Process and device for the temperature-critical joining of two component layers

State of the art

When joining materials that have temperature-critical components, ie components whose melting point is below a melting point of a layer to be joined, it is necessary to limit energy input into the layer to be joined in order to avoid damage to the temperature-critical components.

For example, ultrasonic methods are used to join a copper power connector to a printed circuit board on which temperature-critical components such as capacitors and/or processors are arranged.

However, ultrasonic methods for joining components place high demands on the rigidity of the components to be joined and their surface quality, so that currently only power connectors with a width of up to 2 mm can be joined using an ultrasonic method.

Furthermore, soldering methods are known in which a soft solder is applied whose melting point is below the critical temperature of the respective temperature-critical electronic components.

Furthermore, methods for laser welding of material pairings are known in which an energy input is minimized by the local distance between the energy input and the joint. Disclosure of Invention

As part of the presented invention, a method for temperature-critical joining, a joining device and a semiconductor element are presented. Further features and details of the invention result from the respective dependent claims, the description and the drawings. Features and details that are described in connection with the method according to the invention also apply, of course, in connection with the joining device according to the invention and the semiconductor element according to the invention and vice versa, so that the disclosure of the individual aspects of the invention is or can always be referred to mutually.

The invention presented serves to connect two component layers, of which at least one component layer has a temperature-critical component. In particular, the presented invention serves to enable a copper-to-copper connection of a power connector with a 35 pm metallization for supplying semiconductor elements on a printed circuit board.

A method is thus presented for the temperature-critical joining of a first electrically conductive component layer with a first constant material thickness and a second component layer with a second constant material thickness, with at least one electronic component being arranged on the second component layer, the critical temperature of which is below a melting point of the first and the second layer of components. The method comprises an arrangement step for arranging the first component layer over the second component layer without a gap and a movement step for moving a laser beam with constant power along the first component layer with a welding feed, which causes a material forming the first component layer to be melted by an energy input of the laser beam , and that only material in a surface area of the second component layer is melted by the energy input. In the context of the present invention, a critical temperature of a component is to be understood as meaning a temperature at which the component is damaged.

In the context of the presented invention, a surface area is to be understood as meaning a component layer which is surrounded on one side by a carrier layer, such as a substrate. In particular, a surface area is very thin, e.g. 35 pm, thin. A surface area can be made of metal and can be arranged under a protective layer, which can be made of plastic, for example. Correspondingly, a surface area can form a conductor layer of a printed circuit board.

To join two component layers or two materials, at least one of which has a temperature-critical component, the method presented provides for a welding feed, i.e. a movement of a laser along a first component layer, which is so fast that energy is introduced by welding limited to a very small weld area. The limitation of the welding area occurs on the one hand in its surface area, ie its cross section on the first component layer, but also in its depth extension in a second component layer arranged under the first component layer.

The welding feed provided according to the invention limits an energy input into a second component layer, which is arranged under a first component layer, in such a way that only material in a surface area of the second component layer is melted. This effect can be checked easily, for example by making a section through a material combination produced using the method according to the invention. In this case, however, the energy input is at least so high that the first component layer is continuously melted and energy introduced into the first component layer is passed on to the second component layer.

The first component layer becomes the first component layer as a result of the inventively provided melting of the first component layer up to the second component layer continuously melted, so that a melt of the first component layer contacts the second component layer and forms a connection with it. Due to the welding feed provided according to the invention, penetration of the second component layer by the melt is avoided, so that the second component layer is only melted in a surface area and minimal energy is introduced into the second component layer.

Due to the minimal energy input into the second component layer caused by the method according to the invention, an energy input into components arranged on the second component layer, such as processors or other switching elements, in particular capacitors or insulators, is also minimized. Accordingly, heating of components arranged on the second component layer when the method according to the invention is carried out remains far below a critical temperature of respective components arranged on the second component layer, so that damage to the components by the method according to the invention is avoided.

It can be provided that the welding feed rate is at least 800mm/s.

The welding feed rate provided according to the invention is at least 800mm/s, so that a respective localized area of the first and second component layer is only temporarily or briefly thermally stressed and a localized energy input remains minimal or is only so large that the second component layer is melted in its surface area .

Since so-called "humping" usually already occurs at a welding feed rate of 800mm/s, such a welding feed rate is usually avoided. However, according to the invention, by using a laser and a gap-free arrangement of component layers to be connected, humping can be reliably avoided, particularly in the case of small heating areas.

By arranging two component layers without a gap, part of an energy input that is conducted into the first component layer is transferred to the second Transfer component layer, whereby a meta-stable intermediate state of a melt in the first component layer is generated, which avoids humping and also makes it possible to limit melting of the second component layer to a surface area, in particular to a surface area with a material thickness of 35 pm.

Provision can furthermore be made for a cross section of an area with which the laser beam provides the energy input into the first component layer and the second component layer to be at most 75 pm, in particular at most 50 pm or at most 40 pm.

In combination with the welding feed provided according to the invention, a small cross section of an area with which a laser beam provides an energy input into the first component layer and the second component layer leads to the depth of the surface area within which the second component layer is melted being controlled or minimized can be.

While a cross-section of an area with which a laser beam provides an energy input into the first component layer and the second component layer should preferably be small when carrying out the method according to the invention, i.e. at most 75 pm, in particular at most 50 pm or at most 40 pm, the area can be any have length. In particular, the surface can have a length of more than 2 cm, so that, for example, power connectors with a width greater than 2 cm can be joined, in particular bonded, as the first component layer to a second component layer, such as a printed circuit board.

In particular, the method presented can be used to provide a welding area that is longer than 2 cm without damaging the respective temperature-critical components.

Provision can furthermore be made for the first component layer to have a material thickness of at least 80 pm, in particular at least 100 pm and at most 200 pm, and/or for the surface area to have a Material thickness of at most 50pm, in particular at most 35pm.

The method provided according to the invention is particularly suitable for joining power connectors made of copper with a material thickness of approximately 100 μm and a width of more than 2 cm on a circuit board or power electronics with a copper layer of 35 μm.

As an alternative or in addition to the use of copper, it can also be provided that the first component layer and/or the surface area of the second component layer consists at least partly of aluminum, in particular at least partly of copper and/or aluminum.

Provision can also be made for the surface area of the second component layer to be surrounded by the at least one component, and for the at least one component to comprise at least one element from the following list of elements: printed circuit board, capacitor, ceramic substrate, semiconductor element, chip.

In particular, the component provided according to the invention can be part of power electronics or a semiconductor element, such as a printed circuit board or a control device, or be a battery.

Provision can furthermore be made for a laser beam with a wavelength of 1030 nm and/or a power of between 750 watts and 1.5 kW, in particular between 750 watts and 1 kW, to be used.

It has been shown that a laser beam of in particular approx. 1 kW in combination with a cross section of approx. 50 pm and a welding feed of approx. 800 mm/s is particularly advantageous for carrying out the method presented and accordingly for melting a second component layer at a maximum depth of 35 pm if the first component layer has a thickness of 100 pm. In a second aspect, the presented invention relates to a joining device for the temperature-critical joining of a first electrically conductive component layer with a first constant material thickness and a second component layer with a second constant material thickness, wherein at least one electronic component is arranged on the second component layer, the critical temperature of which is below a Melting point of the first and the second component layer is. The joining device includes a laser, an actuator and a control unit. The control unit is configured to control the actuator in such a way that the actuator moves the laser with a welding feed over the first component layer, which causes a material forming the first component layer to be partially melted down to the second component layer by an energy input from the laser beam , and that only material in a surface area of the second component layer is melted by the energy input.

The joining device according to the invention serves in particular to carry out the method according to the invention.

In a third aspect, the presented invention relates to a semiconductor element. The semiconductor element comprises a first electrically conductive component layer with a first constant material thickness and a second component layer with a second constant material thickness, the first component layer and the second component layer being connected using a possible configuration of the method presented.

Provision can be made for the first component layer and the second component layer to be connected without solder.

In particular, the first component layer and the second component layer of the semiconductor element according to the invention are connected in such a way that a solidified melt in a connection region of the second component layer projects only into a surface region of the second component layer.

The joining of two component layers provided according to the invention allows two components to be connected in an electrically conductive manner without the need for a solder is needed. In particular, the presented invention enables second copper layers to be melted, so that the copper layers form a connection with one another that is electrically conductive and mechanically stable.

Show it:

Figure 1 shows a schematic representation of a possible embodiment of the method according to the invention,

FIG. 2 shows a schematic representation of a possible embodiment of the joining device according to the invention,

FIG. 3 shows a schematic representation of a possible configuration of the semiconductor element according to the invention.

A sequence of a method 100 is shown in FIG. An energy input into a first component layer 103 and a second component layer 105 is provided by means of a laser beam 101, which is set to a power “P”.

The laser beam 101 is moved along a surface of the first component layer 103 with a welding feed rate, ie a speed “v”, as indicated by arrow 107 . Accordingly, a melting area 109 is created in the first component layer 103 and the second component layer 105. The melting area 109 extends completely through the first component layer 103 and into a surface area 111 of the second component layer 105. Correspondingly, a support area 113 lying under the surface area 111 becomes the second component layer 105 is not melted.

A section-specific energy input E, which is introduced into the first component layer 103 and the second component layer 105, results from the ratio of the power of the laser beam 101 and the welding feed. According to the invention, the welding feed rate is selected to be as high or as fast as possible without generating instabilities through so-called "humping". The power of the laser beam is increased until a desired welding depth is reached is reached. The larger the cross-section of a welding area, the more energy has to be provided to reach the required welding depth.

In particular, the welding feed rate can be selected in such a way that it leads to a metastable intermediate state of a molten slag. Within this intermediate state, there is still no “humping”, ie slag escaping from the melting region 109, but the slag can be set in dynamic motion, which enables energy to be dissipated quickly from the surface area of the second component layer.

For example, in the situation shown in FIG. 1, the laser beam 101 is operated with a power of 1 kW and is moved with a welding feed rate of at least 800 mm/s, as indicated by arrow 107. As a result, in the first component layer 103, which is 100 μm high, the welding area 109 with a cross section of 40 μm is created. In the welding area 109, the first component layer 103 melts completely and in the second component layer 105 in some areas, only in the surface area 111, which is e.g. 35 μm high here.

Due to the welding advance of the laser beam 101, the energy transmitted by the laser beam 101 acts only locally in the melting region 109, so that a transmission of energy provided by the laser beam 101 into an area 115 of the first component layer 103 surrounding the melting region 109 and an area surrounding the melting region 109 117 of the second component layer 105 is minimized.

The realization that humping is not pronounced with a 40 pm laser spot at a laser wavelength of 1030 nm and that the depth of pores occurring during the welding process is speed-dependent allows the method 100 to be carried out with minimal heat input into the second component layer 105 in particular and yet a stable mechanical connection between the first component layer 103 and the second component layer 105. A joining device 200 is shown in FIG. 2 . The joining device 200 includes a laser 201, an actuator 203 and a control unit 205. The control unit 205 is configured to control the actuator 203 in such a way that the actuator 203 moves the laser 201 with a welding feed over a first component layer, which causes through an energy input of a laser beam of the laser 201, a material forming the first component layer is partly melted up to a second component layer, and that only material in a surface area of the second component layer is melted by the energy input.

In particular, the control unit 205 is configured to minimize an energy input by the laser 201 into areas of the first component layer and the second component layer surrounding a welding area, by the process parameters welding feed rate, power of the laser and cross-section of the welding area being adjusted to one another, with the welding feed rate being at least is 800mm/s.

FIG. 3 shows a semiconductor element 300 that was produced using the method 100 .

A power connector 301 which is arranged above a circuit board 303 can be seen here. The power connector 301 and the circuit board 303 are connected via a welding portion 305 .

The weld area 305 provides a mechanical and electrically conductive connection between the power connector 301 and the circuit board 303 . For this purpose, the power connector 301 and the printed circuit board 303 are connected without solder.

The welding area 305 extends completely through the power connector 301 and into a surface area 307, in this case a copper metallization of the printed circuit board 303. Here it is easy to see that the welding area 305 does not extend into a carrier layer 309 of the printed circuit board 303. Correspondingly, the carrier layer 309 can be made of temperature-sensitive material, such as plastic. A gap between the power connector 301 and the copper metallization can arise due to energy provided during the production of the semiconductor element 300, which gap can be caused, for example, by melted plastic of the printed circuit board 303.

Claims

Expectations

1. Method (100) for the temperature-critical joining of a first electrically conductive component layer (103, 301) with a first constant material thickness and a second component layer (105, 303) with a second constant material thickness, wherein on the second component layer (105, 303) at least an electronic component is arranged, the critical temperature of which is below a melting point of the first component layer (103, 301) and the second component layer (105, 303), and wherein the method (100) comprises the following steps:

- arranging the first component layer (103, 301) without a gap over the second component layer (105, 303),

- Moving a laser beam (101) with constant power along the first layer of components (103, 301) with a welding feed which causes a material forming the first layer of components (103, 301) to be partially melted by energy input from the laser beam (101) up to of the second component layer (105, 303) is melted, and that only material in a surface region (111, 307) of the second component layer (105, 303) is melted by the energy input.

2. Method (100) according to claim 1, characterized in that the welding feed rate is at least 800 mm/s.

3. The method (100) according to claim 1 or 2, characterized in that a cross section of an area with which the laser beam (101) provides the energy input into the first component layer (103, 301) and the second component layer (105, 303), is at most 75pm, in particular at most 50pm or at most 40pm.

4. The method (100) according to any one of the preceding claims, characterized in that the first component layer (101, 301) has a material thickness of at least 80 μm, in particular at least 100 μm and at most 200 μm, and/or that the surface area (111, 307) of the second component layer (105, 303) has a material thickness of at most 50 pm, in particular at most 35 pm.

5. The method (100) according to any one of the preceding claims, characterized in that the first component layer (101, 301) and/or the surface area (111, 307) of the second component layer (105, 303) is at least partially made of copper and/or aluminum.

6. The method (100) according to any one of the preceding claims, characterized in that the surface area (111, 307) of the second component layer (105, 303) is surrounded by the at least one component, and that the at least one component contains at least one element of the following List of items includes: circuit board, capacitor, ceramic substrate, semiconductor element, chip.

7. The method (100) according to any one of the preceding claims, characterized in that the laser beam (101) is used with a wavelength of 1030 nm and/or a power of between 750 watts and 1.5 kW, in particular between 750 watts and 1 kW will.

8. The method (100) according to any one of the preceding claims, characterized in that the second component layer (105, 303) is part of power electronics. - 14 - Joining device (200) for the temperature-critical joining of a first electrically conductive component layer (101, 301) with a first constant material thickness and a second component layer (105, 303) with a second constant material thickness, wherein on the second component layer (105, 303) at least one electronic component is arranged, the critical temperature of which is below a melting point of the first and the second component layer (105, 303), the joining device (200) comprising:

- a laser (201),

- an actuator (203),

- a control unit (205), wherein the control unit (205) is configured to control the actuator (203) in such a way that the actuator (203) moves the laser (201) with a welding feed over the first component layer (101, 301). , which causes a material forming the first component layer (101, 301) to be partially melted down to the second component layer (105, 303) by an energy input from the laser beam (101), and that the energy input only melts material in a surface area ( 111, 307) of the second component layer (105, 303) is melted. Joining device (200) according to Claim 9, characterized in that the joining device (200) is configured to carry out a method (100) according to one of Claims 1 to 8. Semiconductor element (300), comprising a first electrically conductive component layer (301) with a first constant material thickness and a second component layer (303) with a second constant material thickness, wherein the first component layer (301) and the second component layer (303) have been connected by means of a A method according to any one of claims 1 to 8. - 15 - The semiconductor element (300) according to claim 11, characterized in that the first device layer (301) and the second device layer (303) are connected without solder.