WO2023083960A1

WO2023083960A1 - Joining method and anvil for use in a joining method

Info

Publication number: WO2023083960A1
Application number: PCT/EP2022/081464
Authority: WO
Inventors: Michael Timmermann; Nils Lukat; Hauke Markschat; Owe Petersen
Original assignee: Danfoss Silicon Power Gmbh
Priority date: 2021-11-10
Filing date: 2022-11-10
Publication date: 2023-05-19
Also published as: DE102021129286A1

Abstract

A joining method (100) for joining a first joining member (101) and a second joining member (103). The method (100) comprises placing (105) the second joining member (103) on a contact material (107) that changes its stiffness depending on a rate of change of mechanical stress applied to the contact material (107), placing (109) the first joining member (101) on the second joining member (103), and applying (111) mechanical stress to the contact material (107) by moving the first joining member (101) relative to the second joining member (103). Further, the present invention relates to an anvil.

Description

Joining method and anvil for use in a joining method

The present invention relates to a Joining method for joining a first joining member and a second joining member, an anvil, and the use of a contact material that changes its stiffness depending on a rate of change of mechanical stress applied to the contact material for joining a first joining member and a second joining member by use of ultrasonic waves.

For joining of two joining members, ultrasonic based techniques, such ultrasonic welding or wire or ribbon bonding, are known. Such techniques are based on ultrasonic waves generated by an ultrasonic wave generator, boosted and introduced into the joining members by a device known as a “sonotrode”. In particular, the sonotrode moves the first joining member relative to a second joining member that is placed on an anvil.

Usually, the surfaces of the anvil and the second joining member do not fully match, due to a curvature of the second joining member and/or the anvil, or irregularities in the surfaces of either the second joining member or the anvil. Thus, a space exists between the anvil and the second joining member, which leads to a deformation of the second joining member under the pressure of the sonotrode. Such a deformation may lead to cracks in the second joining member, in particular in case of rigid material, such as a substrate of a power unit, for example.

US 2015/0306701 A1 describes an apparatus with an abutment for the arrangement of a substrate. The abutment has first and second partial abutments, wherein the second partial abutment is an elastic shaped body with a modulus of elasticity of between 10 and 500 N/mm², which has a damped effect on a welding connection. Thus, a pneumatic intake device and a clamping device are needed to hold an object to be welded on the surface of the second partial abutment in a force-fitting manner.

Against this background, it is a problem to be solved by the present invention to provide for a possibility for preventing material damage during an ultrasonic joining process.

This problem is solved by the subject-matter of the accompanied claims.

According to a first aspect, the present invention relates to a Joining method for joining a first joining member and a second joining member. The method comprises placing the second joining member on a contact material that changes its stiffness depending on a rate of change of mechanical stress applied to the contact material, placing the first joining member on the second joining member, and applying mechanical stress to the contact material by moving the first joining member relative to the second joining member. The method disclosed herein is based on the principle that a special contact material is used for making a connection to a second joining member. This contact material is “dynamic”, which means that it changes its stiffness depending on a rate of change of mechanical stress applied to the contact material. In other words, the contact material has the characteristic that is becomes stiffer the higher the rate of change of mechanical stress applied to the contact material is. Thus, in case a constant force is applied to the contact material, the contact material does not change its stiffness and will remain elastic, whereas in case a changing force, such as an alternating swinging movement of a sonotrode is applied to the joining members and transmitted by these into the contact material, the contact material will become stiff, i.e. stiffer than in case no force or a constant force is applied to the contact material.

The characteristics of the contact material used in the method disclosed herein have the effect, that the contact material in general is in a rubbery-state or visco-liquid-state. Thus, the contact material can adapt to the shape of a particular second joining member attached to the contact material under constant or slowly, in particular gradually changing pressure, such that no space remains between the second joining member and the contact material. Thus, after the second joining member has been slowly attached to, or placed on, the contact material, the contact material is in close and continuous contact with the second joining member.

When a force is applied to the contact material with a high rate of change, i.e. a rate of change that is above a threshold, the contact material becomes stiff, i.e. stiffer than in the rubbery-state or visco-liquid-state. This means that deformation of the second joining member under the applied force, which may cause cracking of the second joining member, is prevented. Further, the stiffened contact material does not have a damping effect on a joining process of the first joining member and the second joining member since energy is not lost into the contact material.

According to an embodiment, the mechanical stress is applied to the contact material by a sonotrode that moves the first joining member relative to the second joining member by ultrasonic waves coupled into the sonotrode by an ultrasound generator.

Since the contact material stiffens under a high rate of change of stress, the contact material stiffens sharply as soon as a movement of the first joining member is induced by ultrasonic waves. The movement of the first joining member is transferred to the second joining member and transferred from the second joining member to the contact material. The contact material becomes hard, in particular as hard as a prior-art anvil, as soon as ultrasonic waves are coupled into the contact material.

According to another embodiment, the contact material is placed on an anvil or part of an anvil.

The contact material may be part of an anvil as a surface layer of a contact area for making contact with a material to be held. The contact material may be provided as a cushion placed in a recess in the surface layer of the anvil or may form a surface layer itself that is attached to a base of the anvil.

Alternatively, the contact material may be provided on an anvil by placing a cushion or layer of the contact material on a contact surface of an anvil. Thus, any anvil may be used to carry out the method disclosed herein by using an additional or separate contact material.

According to another embodiment, the second joining member is placed on the contact material with a gradual force, which allows the contact material to fill any space between the second joining member and the contact material.

By using a gradual force that changes with a constant low rate, the contact material will be kept in its rubbery-state or visco-liquid-state. Thus, the contact material will be deformed and, due to this, adapted to the surface to a second joining member brought into contact with the contact material.

According to another embodiment, the contact material includes a non-Newtonian fluid, such that the contact material reversibly gets stiffer the higher the frequency of the mechanical stress applied to the contact material is.

The non-Newtonian fluid may be bound in a gel or a pocket of a fluid-tight material.

According to another embodiment, the contact material is a shear stiffening gel.

In particular, the contact material may be a co-called “silly putty” gel or any other material that has a modulus of elasticity or viscosity that changes with increasing external strain rates.

According to a second aspect, the present invention relates to an anvil for use in a joining method for joining a first joining member and a second joining member by use of ultrasonic waves, wherein the anvil comprises a contact material that changes its stiffness depending on a rate of change of mechanical stress applied to the contact material. The anvil disclosed herein is based on the contact material described with respect to the joining method disclosed herein. The contact material may be provided on a contact surface of the anvil as a cushion or layer of the contact material. Thus, contact material may be reversibly attached to a base of the anvil, such that the contact material may be changed due to varying operating conditions, for example.

According to an embodiment, the contact material is a shear stiffening gel, such as so-called “silly putty” or a non-Newtonian fluid comprising material.

According to a third aspect, the present invention relates to the use of a contact material that changes its stiffness depending on a rate of change of mechanical stress applied to the contact material in a joining method for joining a first joining member and a second joining member by use of ultrasonic waves, wherein the joining method may be ultrasonic bonding or ultrasonic welding.

BRIEF DESCRIPTION OF THE DRAWINGS

Hereinafter, preferred embodiments of the present disclosure will be described with reference to the accompanying drawings. In the drawings:

Fig. 1 shows an embodiment of a joining method according to the present invention,

Fig. 2 shows an embodiment of an anvil according to the present invention.

DETAILED DESCRIPTION

First, it should be understood by those skilled in the art that these embodiments are only used to explain the technical principles of the present disclosure, and are not intended to limit the scope of protection of the present disclosure. For example, although the following embodiments are explained in conjunction with an apparatus, this is not limitative. The technical solutions of the present disclosure are also applicable to other devices. Such a change to application object does not deviate from the principle and scope of the present disclosure.

In addition, it should also be noted that in the description of the present disclosure, unless otherwise clearly specified and defined, terms “dispose”, “install”, “connect” and “connection” should be understood in a broad sense; for example, the connection may be a fixed connection, or may also be a detachable connection, or an integral connection; it may be a mechanical connection, or an electrical connection; it may be a direct connection, or an indirect connection implemented through an intermediate medium, or it may be an internal communication between two elements. For those skilled in the art, the specific meaning of the above terms in the present disclosure can be understood according to specific situations.

In Fig. 1 , a joining method 100 for joining a first joining member 101 and a second joining member 103 is shown.

The method 100 comprises a first placing step 105, in which the second joining member 103 is placed on a contact material 107 that changes its stiffness depending on a rate of change of mechanical stress applied to the contact material 107, such a shear stiffening gel, for example.

In a second placing step 109, the first joining member 101 is placed on the second joining member. Of course, the second placing step may be carried out before carrying out the first placing step, such that the first joining member 101 is placed on the second joining member 103 before the second joining member 103 is placed on the contact material 107. Thus, a combination of the first joining member 101 and the second joining member 103 is placed on the contact material 107.

Further, the second joining member 103 is moved and pressed into the contact material 107 with low and constant or gradually increasing force applied by a sonotrode 113. Accordingly, the contact material 107 adapts to the shape of the second joining member 103, such that there remains no space between the second joining member 103 and the contact material 107. Thus, the contact material 107 supports the second joining member 103 perfectly when the contact material becomes stiff.

In a joining step 111 , mechanical stress is applied to the first joining member 101 by moving the first joining member 101 relative to the second joining member 103, as indicated by arrow 115. Since this mechanical stress is transferred to the contact material 107 by the second joining member 103, the contact material 107 stiffens, and movement of the second joining member 103 is blocked by the stiffened contact material 107. Finally, the first joining member 101 and the second joining member 103 are welded together in an ultrasonic welding process.

Since there is no space between the second joining member 103 and the contact material 107, the second joining member 103, which may be a substrate of a power module, for example, cannot be deformed and cannot break during the welding process. As shown in Fig. 1 the contact material 107 may become stiff only in an area 117 that is stressed by the ultrasonic welding process.

In Fig. 2 an anvil 200 is shown. The anvil 200 comprises a base 201 and a contact surface 203 for holding a joining member, such as the second joining member 103 according to Fig. 1 .

On the contact surface 203, a contact material, such as contact material 107 according to Fig. 1 is provided that changes its stiffness with respect to a rate of change of mechanical stress applied to the contact material 107. Thus, the contact material 107 becomes stiffer the higher the change rate of mechanical stress applied to the contact material 107 is.

The contact material 107 is provided as a cushion that receives the second joining member 103 in a constant movement in preparation for an ultrasonic welding process, where the contact material 107 becomes stiff, in particular hard, under the influence of the ultrasonic waves.

The contact material 107 is a gel, for example. The contact material 107 comprises preferably a shear stiffening material such as a shear thickening fluid (STF) system or a shear stiffening gel (SSG) system.

An STF is a type of non-Newtonian suspension liquid obtained by dispersing micro and nanoparticles into a polar medium such as ethylene glycol or polyethylene glycol.

There are generally three types of common dispersed phase particles in STF systems: inorganic mineral particles (such as SiO2, CaCO3 or Ti02), variable particles (such as cornstarch particles), and finally synthetic polymer particles (such as polyvinyl alcohol (PVA), polystyrene acrylonitrile (PS-AN), and polystyrene-ethyl acrylate (PSt-EA)).

A shear thickening gel (SSG) may comprise a gel-like polymer blend without a solvent. Examples include a boron-siloxane polymer silicone rubber with a low crosslinking degree, which is often synthesized using polysiloxane dimethyl silicone oil or hydroxy silicone oil, boric acid, and benzoyl peroxide (BPO) at high temperature.

Hitherto, the technical solutions of the present disclosure have been described in conjunction with the preferred embodiments shown in the accompanying drawings, but it is easily understood by those skilled in the art that the scope of protection of the present disclosure is obviously not limited to these specific embodiments. Without departing from the principle of the present disclosure, those skilled in the art can make equivalent changes or replacements to relevant technical features, and the technical solutions after these changes or replacements will fall within the scope of protection of the present disclosure.

Reference signs

100 jommg method

101 first joining member 103 second joining member

105 first placing step

107 contact material

109 second placing step

111 joining step 113 sonotrode

115 arrow

117 area

200 anvil

201 base 203 contact surface

Claims

- 9 - C LAI MS

1. Joining method (100) for joining a first joining member (101) and a second joining member (103), the method (100) comprising: placing (105) the second joining member (103) on a contact material (107) that changes its stiffness depending on a rate of change of mechanical stress applied to the contact material (107), placing (109) the first joining member (101) on the second joining member (103),

- applying (111) mechanical stress to the contact material (107) by moving the first joining member (101) relative to the second joining member (103).

2. Joining method (100) according to claim 1 , wherein the mechanical stress is applied to the contact material (107) by a sonotrode (113) that moves the first joining member (101) relative to the second joining member (103) by ultrasonic waves coupled into the sonotrode (113) by an ultrasound generator.

3. Joining method (100) according to claim 1 or 2, wherein the contact material (107) is placed on an anvil (200) or a part of an anvil (200).

4. Joining method (100) according to any of the preceding claims, wherein second joining member (103) is placed on the contact material (107) with a gradual force, which allows the contact material (107) to fill any space between the second joining member (103) and the contact material (107).

5. Joining method (100) according to any of the preceding claims, wherein the contact material (107) includes a non-Newtonian fluid, such that the contact material (107) reversibly gets stiffer the higher the mechanical stress applied to the contact material (107) is.

6. Joining method (100) according to any of the preceding claims, wherein the contact material (107) is a shear stiffening gel.

7. Anvil (200) for use in a joining method (100) for joining a first joining member (101) and a second joining member (103) by use of ultrasonic waves, wherein the anvil (200) comprises a contact material (107) that changes its stiffness depending on a rate of change of mechanical stress applied to the contact material (107). Anvil (200) according to claim 7, wherein the contact material (107) is a shear stiffening gel. Use of a contact material (107) that changes its stiffness depending on a rate of change of mechanical stress applied to the contact material in a joining method (100) for joining a first joining member (101) and a second joining member (103) by use of ultrasonic waves. Use of a contact material (107) according to claim 9, wherein the joining method (100) is ultrasonic bonding or ultrasonic welding.