Contact system with a contact carrier and a bonding wire

Abstract

The invention relates to a contact system. The contact system comprises a contact carrier and an electrical connection with a contact surface arranged on the contact carrier. The contact system also comprises a bonding wire, the contact surface of which is configured to be connected to the bonding wire by ultrasonic welding. The contact surface of the connection has a projection, in particular a pedestal, a hump, or a ridge. The projection is configured to be connected to the bonding wire, in particular by ultrasonic welding. The projection preferably has at least one ramp tapered away from the contact carrier.

Description

State of the art

[0001] The invention relates to a contact system. The contact system comprises a contact carrier and an electrical connection arranged on the contact carrier with a contact surface. The contact system also comprises a bonding wire, wherein the contact surface is designed to be connected to the bonding wire by ultrasonic welding.

[0002] From WO 2011 130 205 A2 a support system for a semiconductor for wire or ribbon bonding is known. Disclosure of the invention

[0003] According to the invention, the contact surface of the contact system of the type mentioned above, in particular of the terminal, has a projection, in particular a pedestal, a bump, or a web. The projection, in particular the contact surface, is designed to be connected to the bonding wire, in particular ultrasonically welded. The projection preferably has at least one ramp tapered away from the contact carrier.

[0004] This can advantageously reduce or prevent stress during bonding and thus prevent crack formation in the contact carrier.

[0005] In a preferred embodiment, the at least one ramp adjoins the contact surface. This advantageously allows mechanical vibration, or vibration input into the projection, to be introduced into the contact carrier with an impedance that gradually transitions into the contact carrier. This advantageously prevents cracks or the formation of cracks.

[0006] In a preferred embodiment, the projection is formed by a truncated pyramid or a truncated cone. Advantageously, the projection can be produced in the contact carrier in a cost-effective manner, for example, by electroplating, using an additive manufacturing process, in particular laser sintering, 3D printing, or by removal, for example, milling, or laser ablation.

[0007] In a preferred embodiment, the ramp is concave. This advantageously allows for a gradual impedance transition from the projection to the contact carrier.

[0008] In a preferred embodiment, the contact surface of the terminal, in particular the projection, is groove-shaped. Advantageously, the bonding wire can be easily inserted into the groove and finds a secure hold there during the bonding process. It has also been recognized that the groove can also reduce the likelihood of crack formation. The vibration energy introduced into the projection during ultrasonic welding of the bonding wire to the projection can thus advantageously flow at least partially into the groove edges and be dissipated there.

[0009] In a preferred embodiment of the contact system, the bonding wire is a round wire, with a radius of curvature of the contact surface corresponding to a cross-sectional radius of the bonding wire. The round wire preferably has a round, in particular circular, or elliptical cross-section. Advantageously, a contact surface of the bonding wire can thus be friction-welded, in particular ultrasonically welded, to the contact surface of the projection with minimal force.

[0010] In a preferred embodiment of the contact system, lamellae or webs are formed on the contact surface, deflecting away from the contact surface. Preferably, grooves are formed between the lamellae or webs that are immediately adjacent to one another. This advantageously allows the bonding wire to melt into the lamellae during ultrasonic welding, and thus also absorbs part of the vibration energy by deforming the lamellae.

[0011] The lamellae preferably have a ratio between a lamella height and a lamella thickness of more than 2:1 or more than 3:1. The distance between adjacent lamellae is preferably less than or equal to one-fifth of the diameter of the bonding wire, in particular of a round bonding wire or the width of a flat bonding wire. Advantageously, the lamellae can thus form an easy-to-bond and sufficiently stable support for the bonding wire.

[0012] In the embodiment of the contact surface with the lamellae, the bonding wire is preferably a bonding ribbon or bonding ribbon. The bonding ribbon formed in this way can advantageously prevent point loading on the contact surface during ultrasonic welding.

[0013] In another embodiment of the contact system, the laminations can be formed independently of a projection on a contact carrier, in particular on a flat bonding surface of the contact carrier. Advantageously, a contact carrier without a projection can thus be ultrasonically welded to a bonding wire or bonding strip in a low-stress manner. For this purpose, the bonding strip or bonding wire is placed on the laminations, and a sonotrode is placed on the bonding wire or bonding strip, thus ultrasonically welding the bonding wire or bonding strip to the laminations.

[0014] In a preferred embodiment of the contact system, the projection is softer in the area of ​​the outward-facing contact surface than in a base area facing the contact carrier. The outward-facing area of ​​the contact surface preferably has a lower Shore hardness than the base area of ​​the projection, which is integrally formed on the contact carrier. This advantageously allows the bonding wire to sink more easily into the surface of the projection during ultrasonic welding.

[0015] In a preferred embodiment, the projection, in particular the projection, comprises a different, in particular harder, material in the region of the ramp than the projection core. The material can be formed, for example, from an alloy different from the projection core or from a metal plating, in particular copper plating. This can advantageously further reduce the likelihood of crack formation in the projection region.

[0016] The projection is preferably made of copper or a copper alloy, an alloy comprising copper and aluminum, or aluminum. The contact surface is preferably formed as a surface region of the projection. Advantageously, the projection can thus provide good current-carrying capacity as well as mechanical protection for the contact carrier during ultrasonic bonding.

[0017] The projection preferably has a height that corresponds to or is greater than the thickness of the terminal, preferably between one and six times, more preferably between two and five times, the thickness of the terminal. The terminal is preferably formed by a metal layer on the contact carrier, in particular a semiconductor or substrate. The metal layer preferably has a thickness between 5 and 50 micrometers, preferably between 20 and 30 micrometers.

[0018] In a preferred embodiment of the contact system, the contact carrier is a semiconductor, preferably a packageless semiconductor switch, also called a bare die. The semiconductor switch is preferably a silicon semiconductor switch or a silicon carbide semiconductor switch. The semiconductor switch is preferably a field-effect transistor, in particular an IGFET (IG = insulated gate), MOS-FET (MOS = metal oxide semiconductor), MIS-FET (MIS = metal insulator semiconductor), or an IGBT (IGBT = insulated gate bipolar transistor). Advantageously, a secure electrical contact can be formed towards the semiconductor switch by means of the projection.

[0019] The terminal is preferably formed by a metal layer, in particular a copper layer or aluminum layer. The projection is preferably formed by a metal block, in particular a copper block or a copper alloy.

[0020] In another embodiment, the contact carrier is a substrate, in particular a ceramic substrate. The substrate is preferably a DCB substrate (DCB = Direct Copper Bonded), AMB substrate (AMB = Active Metal Brazed), IMS substrate (IMS = Insulated Metal Substrate), LTCC substrate (LTCC = Low Temperature Cofired Ceramics), or HTCC substrate (HTCC = High Temperature Cofired Ceramics). The substrate preferably has an electrically insulating ceramic layer, in particular an aluminum oxide layer, and at least one electrically conductive layer, in particular a copper layer or aluminum layer. The projection is preferably integrally bonded to the electrically conductive layer of the substrate, applied to it, or molded onto it.

[0021] The projection can be produced, for example, by means of plasma spray, thermal spraying, laser sintering, or galvanically on the terminal or the substrate, or can be applied to the terminal as a solid metal element and connected to the terminal in a material-to-material manner, in particular by soldering, welding, electrically conductive bonding, or sintering.

[0022] The invention also relates to a method for bonding a bonding wire to a contact carrier, in particular a semiconductor. In the method, the bonding wire is bonded, in particular welded, to a projection formed on the contact carrier using ultrasonic waves, wherein the projection has a ramp that laterally widens the projection. The ramp is designed to gradually conduct ultrasonic energy introduced into the projection during bonding into the contact carrier. This advantageously reduces or prevents crack formation in the contact carrier, in particular the semiconductor, during ultrasonic welding, and / or reduces thermomechanical stress.

[0023] Advantageously, by means of the projection arranged on the contact carrier, a thermomechanical stress introduction, in particular formed by different expansion coefficients of the materials, in particular the material of the bonding wire and the semiconductor, can be advantageously influenced even during operation of the contact carrier, in particular a power semiconductor, so that crack formation can be largely avoided or completely prevented even during operation.

[0024] The invention will now be described below with reference to figures and further exemplary embodiments. Further advantageous embodiments will become apparent from a combination of the features described in the dependent claims and in the figures. Fig. 1 shows an embodiment of a contact system with a truncated pyramid-shaped projection onto which a bonding wire is ultrasonically welded; Fig. 2 shows that in Fig. 1 illustrated contact system in a plan view in which the truncated pyramid shape of the projection area is shown; Fig. 3 shows a contact system with a contact carrier and a projection which is hollow and rises towards a contact surface formed for bonding with a bonding wire; Fig. 4 shows a contact system with a contact carrier and a truncated pyramid-shaped projection arranged on the contact carrier, which has knobs or lamellae formed on a contact surface formed for bonding with a bonding wire for bonding.

[0025] Fig. Figure 1 shows an exemplary embodiment of a contact system 1. The contact system 1 comprises a contact carrier 2, in this exemplary embodiment a semiconductor switch, in particular a bare die. The contact carrier 2 has an electrical connection 3, which in this exemplary embodiment is formed by a metal layer, in particular an aluminum layer, or a copper layer.

[0026] The contact carrier 2 has a projection 4, which in this exemplary embodiment is designed as a trapezoidal pedestal or bump. In this exemplary embodiment, the projection 4 is designed as a copper or aluminum element that is molded onto the contact carrier 2 or, in another embodiment, is connected to the contact carrier 2, in particular to the terminal 3, by soldering or sintering. The projection 4 can be produced by a deposition process, in particular laser sintering, or electroplated, or can be integrally connected to the terminal as a metal element.

[0027] In this exemplary embodiment, the projection 4 has a side surface 5 extending around the projection 4, which is designed as an inclined flank. The projection 4 also has a contact surface 7 designed for ultrasonically bonding to a bonding wire 8, in this example a bonding strip or bonding flat wire, which forms an outward-facing surface of the projection 4. The projection 4 thus has a trapezoidal shape with the inclined side surface 5, so that the projection 4 forms a truncated pyramid or a truncated cone. Instead of the bonding strip, a round bonding wire can be ultrasonically bonded to the projection 4.

[0028] To firmly bond the bonding wire 8, which in this embodiment is designed as a round wire or a flat round wire, to the projection 4, a sonotrode 9—as indicated by an arrow—can be placed on the bonding wire 8, and the bonding wire 8 can be pressed onto the contact surface 7. Ultrasonic vibrations can then be introduced into the bonding wire by means of the sonotrode 9, which can then be ultrasonically welded to the contact surface 7 of the projection 4 by means of the ultrasonic vibrations.

[0029] Fig. 1 also shows a variant for the projection 4, shown in dashed lines, in which the outwardly facing side surface 5 is covered with a cover layer 6. In this exemplary embodiment, the cover layer 6 is a metal layer having a greater hardness, in particular Shore hardness, than the projection 4. The cover layer 6 is formed, for example, from a copper alloy, in particular a copper-zirconium alloy.

[0030] The projection 4 is formed, for example, from copper, in particular pure copper, or a copper alloy. The bonding wire 8 is, for example, a copper wire or an aluminum wire.

[0031] Fig. 2 shows that in Fig. 1 shows a top view of a contact system shown in a sectional view. The projection 4, which forms a truncated pyramid, faces outward with the contact surface 7, which is designed for bonding with the bonding wire 8, and is integrally bonded to the contact carrier 2, in particular to the metal layer forming the connection 3. The inclined side surface 5 is formed circumferentially around the contact surface 7 and can prevent cracking caused by thermomechanical stresses both during ultrasonic bonding and during operation of the contact carrier 2, in particular the power semiconductor.

[0032] Fig. Figure 3 shows an exemplary embodiment of a contact system 10 comprising a contact carrier 11, in particular a power semiconductor, and a bonding wire 16, in particular a round wire with a circular cross-section. The contact carrier 11 has an electrical connection 12 formed by a metal layer. The electrical connection 12 is, for example, a switching path connection of a power semiconductor switch formed by the contact carrier.

[0033] In this embodiment, a projection 13 is integrally connected to the terminal 12, forming a base for bonding the bonding wire 16. The projection 13 has an outwardly facing, concave contact surface 15. The contact surface 15 can thus form a groove into which the bonding wire 16 can be inserted for ultrasonic welding to the projection 13.

[0034] In this embodiment, the projection 13 has a concave side surface 14 which adjoins the contact surface 15 and extends to the electrical connection 12.

[0035] Both by means of the concave, in particular groove-shaped, contact surface 15, and by means of the concave side surface 14 formed circumferentially around the contact surface 15, crack formation caused by thermomechanical stress can be prevented both during bonding and during operation of the power semiconductor formed by the contact carrier 11.

[0036] Fig.4 shows an exemplary embodiment of a contact system 20. The contact system 20 has a contact carrier 21, which in this exemplary embodiment is designed as a power semiconductor. The contact carrier 21 has an electrical connection 22. The electrical connection 22 is formed as an electrically conductive layer, in particular copper or aluminum. The contact carrier 21 also has a projection 23 with a circumferentially formed ramp 26, which is applied to the electrical connection galvanically or by means of an additive manufacturing process or is integrally connected to the electrical connection 22, in particular by soldering or sintering. The projection 23 is formed in this exemplary embodiment as a truncated pyramid-shaped copper block.

[0037] The projection 23 has outwardly facing lamellae on an outwardly facing contact surface 24, designed for bonding with a bonding wire 27, in this embodiment a bonding strip or bonding flat wire, of which a lamella 25 is shown as an example. Instead of the bonding strip 27, a round bonding wire with a circular cross-section can be ultrasonically bonded to the projection 23.

[0038] The lamellae are designed, for example, as longitudinally extending webs or as nubs, particularly cylinders, that protrude from the contact surface. The lamellae are preferably made of copper and / or aluminum or a copper alloy.

[0039] For example, the thickness of the slats is less than half or less than one third of the height of the slats. QUOTES CONTAINED IN THE DESCRIPTION

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

[0000] WO 2011 130 205 A2

[0002]

Claims

[1] Contact system (1, 10, 20) with a contact carrier (2, 11, 21) and an electrical connection (4, 13, 23) arranged on the contact carrier (2, 11, 21) with a contact surface (7, 15, 25) and a bonding wire (8, 16, 27), wherein the contact surface (7, 15, 25) is designed to be connected to the bonding wire (8, 16, 27) by means of ultrasonic welding (9), characterized by in that the terminal (4, 13, 23) has a projection (4, 13, 23), in particular a pedestal, hump or web, which is designed to be connected, in particular welded, to the bonding wire (8, 16, 27) and which has a ramp (5, 14, 26) tapered away from the contact carrier (2, 11, 21). [2] Contact system (1, 10, 20) according to claim 1, characterized by that the ramp (5, 14, 26) connects to the contact surface. [3] Contact system (1, 10, 20) according to claim 1 or 2, characterized by that the projection (4, 13, 23) forms a truncated pyramid or truncated cone. [4] Contact system (1, 10, 20) according to one of the preceding claims, characterized by that the ramp (5, 14, 26) is concave. [5] Contact system (1, 10, 20) according to one of the preceding claims, characterized by that the contact surface (7, 15, 25) is groove-shaped. [6] Contact system (1, 10, 20) according to claim 5, characterized by that the bonding wire (8, 16, 27) is a round wire, wherein a radius of curvature of the contact surface (7, 15, 25) corresponds to a cross-sectional radius of the bonding wire (8, 16, 27). [7] Contact system (1, 10, 20) according to one of the preceding claims, characterized by that on the contact surface (7, 15, 25) there are formed lamellae which deflect away from the contact surface (7, 15, 25). [8] Contact system (1, 10, 20) according to one of the preceding claims, characterized bythat the projection (4, 13, 23) is softer in the region of the outwardly facing contact surface (7, 15, 25) than in a foot region facing the contact carrier. [9] Contact system (1, 10, 20) according to one of the preceding claims, characterized by that the projection (4, 13, 23) in the region of the ramp (5, 14, 26) has a different material than the projection core. [10] Contact system (1, 10, 20) according to one of the preceding claims, characterized by that the contact carrier (2, 11, 21) is a semiconductor switch. [11] Method for bonding a bonding wire (8, 16, 27) to a contact carrier (2, 11, 21), in which a bonding wire (8, 16, 27) is bonded to a projection (4, 13, 23) formed on the contact carrier (2, 11, 21), wherein the projection (4, 13, 23) has a ramp (5, 14, 26) laterally widening the projection (4, 13, 23), and the ramp (5, 14, 26) is designed to gradually conduct ultrasonic energy introduced into the projection (4, 13, 23) during bonding (9) into the contact carrier (2, 11, 21) and / or to reduce thermomechanical stress.

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