Methods for determining the adhesion strength of a metallization

Abstract

Method for testing the adhesion strength of a metallization (10) on a MID substrate (12), wherein a bond wire (14) having a first end (16) and a second end (18) is used, characterized by the following steps: - Connecting the first end (16) of the bond wire (14) to the metallization (10), - Connecting the second end (18) of the bond wire (14) to a bond wire base (20) so that a test bond connection (22) is formed between the metallization (10) and the bond wire base (20), - Inserting a test hook (24) into the test bond connection (22), - Applying a force (F) to the test hook (24) so ​​that a pull-off force acts away from the metallization (10).

Description

[0001] The present invention relates to a method for determining the adhesive strength of a metallization on a substrate according to the preamble of claim 1. State of the art

[0002] Circuit carriers for electronic or mechatronic assemblies are often manufactured using injection-molded plastic components and serve as so-called Molded Interconnected Devices (MIDs) as carriers for conductive traces or metallizations. It is important that the adhesive strength of the applied metallizations is sufficient for the respective application. KR 10 2007 0028571 A discloses a method and a device that provides an improved connection between a chip and a device housing or substrate. Furthermore, a technique for testing the adhesive strength between a chip and a substrate is disclosed. In this technique, adhesive sections applied by thermal compression processes are tested using a pick-and-place system.

[0003] From US patent 2010 0072473 A1, a bond connection between a metallization applied to a substrate and a printed circuit is also known. The bond profile can be modified. Furthermore, the adhesion between a substrate and an object with a flat surface can be quantitatively measured. Disclosure of the invention

[0004] The invention provides a method for determining the adhesive strength of a metallization on a substrate with the features according to claim 1. Preferred embodiments of the method are the subject of the dependent claims. Advantages of the invention

[0005] One aspect of the invention is that, to test the adhesive strength of a metallization on a substrate, a bonding wire is connected to the metallization, the bonding wire having a first end and a second end. A metallization is applied to a MID substrate, and the first end of the bonding wire is connected to the metallization. The second end of the bonding wire is connected to a bonding wire base such that a test bond is formed between the metallization and the bonding wire base by means of the bonding wire. Depending on the chosen embodiment, the second end of the bonding wire can also be connected before the first end of the bonding wire. A test hook is inserted under the test bond. Subsequently, a tensile force is applied to the test hook such that a pull-off force acts on the test bond and thus on the bonding wire base away from the metallization.This tensile force also acts on the connection between the metallization and the MID circuit carrier. The applied tensile force allows the adhesion of the metallization to the MID circuit carrier to be characterized. For example, the shape of the bond wire in the test bond connection can be shaped or bent such that a highest point of the bent bond wire, i.e., a vertex of the bent shape of the bond wire, is located laterally closer to the first end of the bond wire and to the metallization, and thus further away from the base of the bond wire. Additionally, the top surface of the metallization, to which the first end of the bond wire is connected, can be positioned higher than the base of the bond wire.

[0006] Regardless of the bend in the bond wire, it is advantageous to position the test hook closer to, or as close as possible to, the bond wire connection under test, i.e., the first end of the bond wire and the metallization, in order to apply as much force as possible, preferably acting vertically, to the bond wire connection under test. This ensures that the force generated by the test hook acts on the bond wire connection under test to the greatest extent possible.

[0007] The position of the test hook can result in an asymmetrical bond wire shape which supports the tensile force component in the vertical direction.

[0008] Furthermore, the pulling direction of the test hook can be selected so that the highest possible force component is applied vertically to the bond wire connection under test and thus to the metallization. The pulling direction of the test hook also allows for adjustment of the force direction.

[0009] The proposed method allows the adhesion strength of the metallization to be determined on the MID circuit carrier without the result being subject to undesirable fluctuations. Furthermore, the adhesion strength can be determined without the measurement being distorted by the adjacent base material.

[0010] The measures listed in the dependent claims enable advantageous further developments and improvements of the method specified in independent claim 1.

[0011] By determining the tensile force at which the metallization detaches from the MID substrate, a quantitative value can be obtained that characterizes the adhesive force. This can be done without requiring additional temperature modifications, such as a temperature step, which could influence the initial adhesive force.

[0012] In one embodiment of the method, the bond wire base can be designed as a second metallization, which is also applied to the MID substrate. Furthermore, it is possible to apply the bond wire base to a substrate located outside, for example, beneath, the MID substrate. This allows for greater flexibility in creating the test bond, enabling the consideration of the specific topologies present in each case.

[0013] In another embodiment, the dimensions, i.e. the length and width of the metallization, can also be chosen to be small, e.g. between 50 µm and 200 µm, in particular between 80 µm and 150 µm, without negatively affecting the possibility of testing the adhesive force.

[0014] In another embodiment, the bonding wire can be applied to the metallization and / or the bonding wire base by so-called ultrasonic bonding. This method has the advantage that even metallizations applied only to small areas can be tested for adhesion.

[0015] In a further embodiment of the invention, copper or aluminum is selected as the material for the bonding wire. The thickness can range from 50 µm to 600 µm, and in particular from 100 µm to 200 µm. This is advantageous for testing the bond strength, as thicker bonding wires are less prone to breaking during the bond strength determination itself.

[0016] The bond wire base is a bond wire connection, and these terms are used synonymously. Brief description of the characters

[0017] Further features and advantages of the present invention are explained below with reference to exemplary embodiments and the figures. The figures show: Fig. 1 a schematic representation of a test bond connection between metallization areas of a MID layer; Fig. 2 a schematic representation of the procedure for testing the adhesion strength of a metallization on a MID layer. Fig. 3 a schematic representation of a test bond connection between the metallization area of ​​a MID layer and a substrate layer; Fig. 4 A schematic representation of the procedure for testing the adhesion strength of a metallization on a MID layer. Embodiments of the invention

[0018] In the figures, identical reference symbols denote identical or functionally equivalent elements.

[0019] Fig. Figure 1 schematically shows a MID substrate 12. A metallization 10 is applied to the MID substrate 12. The metallization 10 is typically implemented with small geometric dimensions. For example, the length and width of the metallization 10 can be between 50 µm and 200 µm, and particularly between 80 µm and 150 µm. To determine the adhesive strength, especially of such small metallization areas, a first end 16 of a bonding wire 14 is applied to the metallization 10. This can be achieved using methods known in bonding, for example, by friction welding, such as ultrasonic bonding. The second end 18 of the bonding wire 14 is applied to a bonding wire base 20, which in the example shown is also implemented as a metallization. This creates a test bond 22 between the metallization 10 and the metallic bonding wire base 20.

[0020] Fig. Figure 2 schematically illustrates the procedure for determining the adhesive force. A test hook 24 is guided under the test bond 22 such that the test hook 24 engages the test bond 22 without causing damage. To determine the adhesive force, the test hook 24 is subjected to a force F that pulls the test hook 24 away from the surface of the MID substrate 12 and thus away from the metallization 10. The force F is applied, for example, so that it is perpendicular to the surface of the MID substrate 12.

[0021] The force F is increased progressively until the metallization 10 or the metallic bond wire base 20 detaches from the MID substrate 12. In this way, the adhesive force of the metallization 10 on the MID substrate can be quantitatively determined by measuring this detachment force. If only one of the two bond connections shown is to be tested for adhesive strength, the test hook 24 can also be positioned closer to the bond connection under test at the test bond connection 22.

[0022] Preferably, the force is introduced into the bond connection to be tested at the first end 16 of the bond wire in a vertical direction, i.e. along a y-direction perpendicular to a surface of the metallization 10 or of the MID substrate 12.

[0023] Fig. Figure 3 schematically shows another arrangement in which the method can be applied. A MID substrate 12 is applied to a substrate 28. The substrate 28 can, for example, be made of plastic, such as a temperature-resistant plastic like PEEK, wherein the substrate has a metal layer at least in the area of ​​the bond connection. A metallization 10 is applied to the MID substrate 12, which, as already described, is typically designed with small geometric dimensions. The first end 16 of a bond wire 14 is applied to the metallization 10 as already described. The second end 18 of the bond wire 14 is applied to the surface of the substrate 28 using suitable methods. This creates a test bond connection 22 between the metallization 10 and the substrate 28, with the location where the second end 18 of the bond wire 14 is applied serving as the bond wire base 20.In this arrangement, an upper apex 30 of the test bond 22 is positioned along the lateral x-direction closer to the first end 16 of the bond wire 14 of the bond 14 under test than to the second end 18 of the bond wire. The test hook 24 can engage the test bond 22 laterally next to the apex 30 and closer to the bond 16, 10 under test, regardless of the position of the apex 30, in order to apply a large force to the bond wire base 16 under test, and thus to the metallization 10, as schematically illustrated. Preferably, the test hook 24 is guided without tilting along the direction of force F. This prevents lateral sliding of the test hook 24 towards the apex 30 and achieves deformation of the bond wire 14.

[0024] Fig. Figure 4 schematically illustrates the procedure for determining the adhesive force when the bonding wire 14 is fixed to the metallization 10 and the substrate 28. The adhesive force of the metallization 10 is again determined, as already mentioned in connection with Fig. 2 described, determined. When positioning appropriately, it must be taken into account that the test bond connection 22 may be asymmetrically shaped.

[0025] The examples in the Fig. 2 and Fig.The four methods shown have in common that a thick-wire bond is applied to the metallization 10, which in the product is intended, for example, for attaching a small wire bond. In a subsequent tensile test, this test bond 22 is checked for its strength. Using a suitable wire diameter for the test wire 14, the metallization 10 detaches from the MID substrate 12. If the test is successful, this detachment must be destructive.

[0026] For determining the adhesive force, a bonding wire 14 is preferably used, which is typically employed in thick-wire bonding. A copper or aluminum wire with a thickness of 50 µm to 600 µm, particularly 100 µm to 200 µm, is used. The thickness of the bonding wire 14 is selected such that the contact of the bonding wire 14 on the metallization 10 and the bonding wire base 20 is stronger than the holding force of the metallization 10 being tested. When selecting the thickness of the bonding wire 14, it must be ensured that contact of the ends of the bonding wire 16, 18 occurs only on the metallization 10 and the bonding wire base 20, respectively, and that contact with adjacent areas is avoided; otherwise, the result would be distorted. For example, during the bonding process, no bond connection can be formed on a non-metallic surface next to the metallization 10 and / or next to the bond wire base 20.For example, for metallizations 10 with a width of 100 µm, a bonding wire with a diameter of 125 µm can be used.

[0027] The described method can still determine the adhesive strength even when other testing methods, such as pull-off tests with adhesive tapes as well as adhesive and solder connections with subsequent mechanical testing of the adhesion, fail or these methods deliver inaccurate or non-reproducible results.

[0028] The method for testing the adhesion strength of a metallization can be advantageously used in a wide variety of applications. For example, the adhesion strength can be evaluated as early as the development phase of the circuit carrier. Since the adhesion strength depends significantly on the processing, important, positively influencing process parameters can be optimized. Furthermore, the method can be used as a sampling method within the framework of ongoing quality control during the production process. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] KR 10 2007 0028571 A

[0002] US 2010 0072473 A1

[0003]

Claims

[1] Method for testing the adhesion strength of a metallization (10) on a MID substrate (12) wherein a bond wire (14) having a first end (16) and a second end (18) is used, characterized by the following steps: - Connecting the first end (16) of the bond wire (14) to the metallization (10), - Connecting the second end (18) of the bond wire (14) to a bond wire base (20) so that a test bond connection (22) is formed between the metallization (10) and the bond wire base (20), - Inserting a test hook (24) into the test bond connection (22), - Applying a force (F) to the test hook (24) so ​​that a pull-off force acts away from the metallization (10). [2] Method for testing the adhesive strength of a metallization (10) according to claim 1, characterized by , that a detachment force is determined at which the metallization (10) detaches from the MID substrate (12). [3] Method for testing the adhesive strength of a metallization (10) according to claim 1 or 2, characterized by , that the bond wire base (20) is designed as a metallization. [4] Method for testing the adhesive strength of a metallization (10) according to claim 3 characterized by , that the bond wire base (20) is applied to the MID substrate (12). [5] Method for testing the adhesive strength of a metallization (10) according to claim 4, characterized by , that a detachment force is determined at which the metallized bond wire base (20) detaches from the MID substrate (12). [6] Method for testing the adhesive strength of a metallization (10) according to any one of claims 1 to 3, characterized by , that the bond wire base (20) is applied to a substrate (28) that lies outside the MID substrate (12). [7] Method for testing the adhesive strength of a metallization (10) according to any one of claims 1-6 characterized by, that the length and width of the metallization (10) are each between 50 µm and 200 µm, in particular between 80 µm and 150 µm. [8] Method for testing the adhesive strength of a metallization (10) according to any one of claims 1-7 characterized by , that the connection of the first end (16) of the bond wire (14) with the metallization (10) and / or the connection of the second end (18) of the bond wire (14) with the bond wire base (20) is made by ultrasonic bonding. [9] Method for testing the adhesive strength of a metallization (10) according to any one of claims 1-8 characterized by , that a copper or aluminium wire with a thickness of 50 µm to 600 µm, in particular 100 µm to 200 µm, is used as the bond wire (14). [10] Method for testing the adhesive strength of a metallization (10) according to claim 9 characterized by , that the thickness of the bond wire (14) is chosen depending on the distance of the metallization (10) to an adjacent metallization.

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