DE102021207489A1 - Bonding wire, circuit with bonding wire, method for producing a bonding wire and method for producing a circuit - Google Patents

Abstract

Bonding wire (105) with a conductor element (110) for electrically conductively connecting a contact surface of a printed circuit board (125) to a contact surface of a semiconductor element (135), characterized in that the conductor element (110) is encased in an electrically non-conductive insulating layer (115). is.

Description

The present invention relates to a bonding wire, a circuit with a bonding wire, a method for manufacturing a bonding wire and a method for manufacturing a circuit.

Power modules can be used in power electronics as a central switching element in electronic devices. The switching elements can be realized with semiconductors, for example consisting of silicon, silicon carbide or gallium nitride. Bipolar transistors and unipolar field effect transistors can be installed. These semiconductors can be connected on a substrate, which can contain a copper cladding in advance, in which the necessary conductor tracks can be applied in order to be able to switch the respective topology correctly. This is comparable to a two-dimensional structure. However, in order to necessarily include the third dimension, such as skipping copper trenches or contacting the top side of a chip, bonding wires can be used as power lines on a semiconductor module. The shape of the bonding wires can have a decisive influence on the performance of the semiconductor module.

Against this background, the present invention provides an improved bonding wire, an improved circuit with a bonding wire, an improved method for manufacturing a bonding wire and an improved method for manufacturing a circuit according to the independent claims. Advantageous configurations result from the dependent claims and the following description.

The subject matter of this invention is the optimization of bonding wires for use in power modules or circuits. With the bonding wire presented here, the use of material can advantageously be reduced and the electrical performance of a circuit can be increased. In addition, the service life of the bonding wires and sometimes the mold material used can be increased.

A bonding wire with a conductor element for the electrically conductive connection of a contact surface of a circuit board with a contact surface of a semiconductor element is presented. In this case, the conductor element is encased by an electrically non-conductive insulation layer.

The printed circuit board and the semiconductor element can be part of a semiconductor module. The semiconductor element can be a transistor, an integrated circuit or a sensor, for example. According to one embodiment, the semiconductor element is a power transistor. In a corresponding manner, the bonding wire can also be used to produce an electrically conductive connection between contact surfaces of the printed circuit board. The conductor element can be a thin and electrically conductive wire, for example, which can be firmly connected to the contact surfaces, for example by means of a soldering process, and can thus produce an electrically conductive connection between the printed circuit board and the semiconductor element.

The bonding wire can advantageously be used in line electronics. One of the main tasks in hard-switching power electronics can be, among other things, low-loss switching and the resulting overshoot when the semiconductor is switched off. The magnitude of the overvoltage pulse can depend on the factor of the steepness of the commutating current on the one hand and on the structural leakage inductance in the entire commutation cell on the other. In the case of power electronics, the entire leakage inductance can be made up of the leakage inductance of an intermediate circuit, the leakage inductance of a supply line to the so-called power module, and the leakage inductance of the power module. The leakage inductance of a semiconductor module can arise, for example, from the spanned area of the incoming load current and the returning load current. Since the bonding wires within the module can contribute to spanning this area, they can also contribute to the leakage inductance of the module. The so-called loop or curvature of the bonding wires may still be necessary so that clearance and creepage distances can be maintained. A bond loop can advantageously be optimized as small as possible with the bonding wire presented here in order to further optimize the leakage inductance of the semiconductor module to a smaller value. This can lead to lower switching losses as the limit of the overvoltage pulse can be pushed further, which can increase the performance of the inverter. For this purpose, the bonding wire presented here is advantageously encased with an electrically non-conductive insulation layer. The service life of the bonding wires and sometimes of the molding material used can also be increased by using bonding wires with a sheath.

According to one embodiment, the insulation layer can be formed as a cohesive lacquer layer. For example, the insulation layer can be applied to the conductor element as a transparent lacquer layer. To contact the circuit board and the semiconductor element, for example, part of the coated bonding wire with UV be treated. To increase process reliability despite the applied layer of lacquer, this can be modified locally, for example by a UV flash. Advantageously, the conductor element can be varnished quickly and inexpensively.

According to one embodiment, the insulating layer and the conductor element can be movable relative to one another. For example, the conductor element can be surrounded by a coating that is not in material contact with the conductor element. Such a coating can be a thin silicone tube, for example. As a result, the conductor element can advantageously be movable within the insulating layer. In this embodiment, the sheathing does not form a coherent connection with the conductor or with the conductor element, in contrast to, for example, an adhesive bond in the case of paint. Thus, the wire can move slightly relative to the sheath and not be rigidly connected to the sheathing insulation. This has the advantage that the thermal expansion coefficients (CTE) of the individual package materials (mold or silicone gel, wire) can be decoupled. In this way, thermomechanical stress between the materials of the bonding wire and the power module encapsulation can be avoided, which can have a positive effect on the service life of the power module. In this way, signs of fatigue can be avoided, which can typically occur on the bonding wire, which can also be referred to as a bond wire, due to the differences in the individual CTEs and the direct, rigid connection of the materials.

According to one embodiment, the bonding wire can be formed with aluminum and additionally or alternatively copper. For example, the conductor element can be designed as a copper wire or alternatively as an aluminum wire or as an aluminum-silicon wire and encased with an insulating layer. Advantageously, the bonding wire can be produced inexpensively from these materials and can also have optimum electrical and mechanical properties.

According to one embodiment, the bonding wire and/or the conductor element can have a diameter of 10 μm to 500 μm. For example, the bonding wire or the conductor element can have a diameter between 10 μm and 50 μm, between 30 μm and 100 μm, between 100 μm and 200 μm or between 200 μm and 500 μm. The thickness of the bonding wire can be dependent on the electronic circuit in which the bonding wire is to be used. Advantageously, a thickness of the bonding wire can be selected according to the area of use.

According to one embodiment, the insulation layer can be thermally insulating. For example, the conductor element of the bond wire may be heated during use in an electrical system. Due to the thermally insulating sheathing, the molding temperature in the vicinity of the wire can advantageously be lower and the wire being favored as a nucleation site for mold cracks can be avoided due to a flexible connection between the wire and molding material.

According to one embodiment, the bonding wire can have a first end for contacting the contact surface of the printed circuit board, a second end for contacting the contact surface of the semiconductor element and an intermediate section arranged between the first end and the second end, wherein the insulating layer can be arranged exclusively in the intermediate section. For example, the insulating layer can be removed at the ends, which can also be referred to as bonding feet, before integration into a circuit, in order to advantageously enable bonding of the bonding wire to the contact surfaces of the printed circuit board and the semiconductor element, for example by soldering.

In addition, a circuit with a printed circuit board and a semiconductor element is presented, characterized in that a contact surface of the printed circuit board and a contact surface of the semiconductor element are electrically conductively connected to one another by a variant of the previously presented bonding wire. By using a bonding wire with an insulation layer in the circuit presented here, all the advantages mentioned above can be optimally implemented. The bonding wire or another corresponding bonding wire can be used in a corresponding manner in order to connect the contact area of the printed circuit board to a further contact area of the printed circuit board. According to one embodiment, the circuit has a plurality of correspondingly shaped bonding wires for connecting contact areas of the printed circuit board to one another and/or to contact areas of one or more semiconductor elements or other electronic components, such as resistors or plugs.

According to one embodiment, a length of the bonding wire can be less than 1.5 times the distance between the contact surface of the printed circuit board and the contact surface of the semiconductor element or another contact surface of the printed circuit board, depending on the connection for which the bonding wire is used. In other words, the bonding wire can have a curvature or a so-called loop or bonding loop. Bondloops can account for some of the stray inductance of the circuit, for example in the form of a semiconductor module. The curved arrangement of the bonding wires may be necessary so that clearance and creepage distances can be maintained. Advantageously, the size of the bond loops can be optimized in the circuit presented here due to the sheathed bonding wire. By reducing the bond loops on the entire semiconductor module, the leakage inductance caused by the geometry can be reduced. This can increase performance by reducing switching losses and have a positive effect on electromagnetic compatibility, since less leakage inductance in the system can be excited to oscillate. In addition, material can be saved, whereby static resistance can be reduced, and a service life of the semiconductor module can be improved.

In addition, a method for producing a variant of a previously presented bonding wire is presented, the method comprising a step of providing an electrically conductive conductor element and a step of encasing the conductor element with an electrically non-conductive insulation layer in order to produce the bonding wire.

According to one embodiment, the method can have a step of removing part of the insulation layer in order to be able to connect the bonding wire to at least one contact area. For example, the insulation layer can be designed as a non-materially bonded sheath around the conductor element. In this case, for example, the insulation layer can be removed from a first end of the bonding wire for contacting a contact area of a printed circuit board and from a second end for contacting a contact area of a semiconductor element. A bonding process, for example by means of local heating, can thus advantageously be made possible on these uncovered areas of the conductor element.

In addition, a method for producing a variant of the circuit presented above is presented, the method comprising a step of providing a printed circuit board and a semiconductor element and a step of arranging the semiconductor element on the printed circuit board. In addition, the method includes a step of connecting the semiconductor element to the printed circuit board by a variant of the previously presented bonding wire using a bonding method. For example, thermosonic ball wedge bonding (TS bonding) or ultrasonic wedge wedge bonding (US bonding) can be used as the bonding method.

• 1 eine schematische Querschnittsdarstellung eines Ausführungsbeispiels einer Schaltung mit einem Bonddraht;
• 2 eine schematische Querschnittsdarstellung eines Ausführungsbeispiels einer Schaltung mit einem Bonddraht;
• 3 ein Ablaufdiagramm eines Verfahrens zum Herstellen eines Bonddrahts gemäß einem Ausführungsbeispiel; und
• 4 ein Ablaufdiagramm eines Verfahrens zum Herstellen einer Schaltung gemäß einem Ausführungsbeispiel.

The invention is explained in more detail by way of example with reference to the accompanying drawings. Show it:

• 1 a schematic cross-sectional representation of an embodiment of a circuit with a bonding wire;
• 2 a schematic cross-sectional representation of an embodiment of a circuit with a bonding wire;
• 3 a flowchart of a method for producing a bonding wire according to an embodiment; and
• 4 a flow chart of a method for producing a circuit according to an embodiment.

In the following description of preferred exemplary embodiments of the present invention, the same or similar reference symbols are used for the elements which are shown in the various figures and have a similar effect, with a repeated description of these elements being dispensed with.

1 shows a schematic cross-sectional view of an exemplary embodiment of a circuit 100 with a bonding wire 105. The bonding wire 105 comprises an electrically conductive conductor element 110, which in this exemplary embodiment is embodied as a copper wire with a diameter of just 15 µm, for example, and which is covered by an electrically non-conductive insulating layer 115 is encased. In this exemplary embodiment, the insulation layer 115 is designed as a cohesive lacquer layer, merely by way of example. In the illustration shown here, the bonding wire forms an electrically conductive connection between a contact surface 120, a printed circuit board 125 and a contact surface 130 of a semiconductor element 135. In this exemplary embodiment, a length of the bonding wire 105 is, for example, less than 1.5 times the distance 140 between the contact surface 120 of the printed circuit board 125 and the contact surface 130 of the semiconductor element 135. The distance 140 can refer to a direct connection between the contact surfaces 120, 130, in particular between attachment points of the bonding wire 105 to the contact surfaces 120, 130. The bonding wire 105 has due to the slight excess length, only a slight curvature, which can also be referred to as a bond loop. The height 145 of the bonding loop is limited by the air and creepage distances to be maintained, with the bonding loop of bonding wire 105 being able to have a lower height 145 due to the insulation layer 115 than another, for example non-insulated bonding wire 150, which is shown in this figure for comparison with bonding wire 105 is shown.

In contrast to the bonding wire 105, the other bonding wire 150 has no insulating layer and is correspondingly formed with a bonding loop of a height 155 which, for example, corresponds to four times the height 145 of the bonding loop of the bonding wire 105.

The insulation layer 115 of the bonding wire 105 thus enables close alignment along the copper contacts of the printed circuit board 125 or of the semiconductor element 135, as a result of which the bonding wire 105 allows the commutation loop to be made significantly smaller. Accordingly, less material is required for bonding wire 105 than for the other bonding wire 150.

During operation of the circuit 100 shown here, a leakage inductance of the circuit 100 arises, for example in the form of a semiconductor module, among other things from the spanned area of the outgoing load current and the returning load current. Since the bonding wires within the module help to span this area, they also contribute to the leakage inductance of the module. By reducing the bond loop by using the coated bonding wire 105, the leakage inductance of the semiconductor module has a lower value than when using the non-insulated other bonding wire 150. This leads to lower switching losses, since the limit of the overvoltage pulse is further exhausted, which improves the performance, for example inverter increased. The circuit 100 is therefore, for example, a semiconductor module of an inverter.

Also who in 1 only a single bond wire 105 is shown, the circuit 100 may have a plurality of corresponding bond wires 105 . In this way, a plurality of contact surfaces of the printed circuit board 125 can be electrically conductively connected to a plurality of contact surfaces of the semiconductor element 135 or other electronic components. Correspondingly, such a bonding wire can be used to produce an electrically conductive connection between contact surfaces of printed circuit board 125, for example to produce a connection between contact surface 120 and a further contact surface 160 of printed circuit board 125.

2 shows a schematic cross-sectional representation of an embodiment of a circuit 100 with a bonding wire 105. The circuit 100 shown here and the bonding wire 105 correspond to or are similar to the circuit written in the previous figure and the bonding wire described, with the difference that in this embodiment the insulation layer 115 and the conductor element 110 are movable relative to each other. The structure of the bonding wire 105 is shown here in a 2 B clarifies in the a section of the in the 2A shown bonding wire is shown enlarged. The insulation layer 115 in this exemplary embodiment is thermally insulating and forms a non-cohesive sheathing of the conductor element 110, which is only exemplary in the form of an aluminum wire. In other words, the exemplary embodiment shown here differs from that described in the previous figure in that the insulation layer 115 does not have a coherent connection, such as an adhesive bond in the case of paint, with the conductor element 110. Thus, the wire is easily movable with respect to the sheath and is not rigidly connected to the sheathing insulation. As a result, no thermomechanical stress occurs between the materials of the bonding wire 105 and the semiconductor element 135, which has a positive effect on the service life of the semiconductor element 135 and also of the circuit 100. In another exemplary embodiment, signs of fatigue can occur on the bonding wire 105 due to the differences in the individual coefficients of expansion and the direct, rigid connection of the materials. In this exemplary embodiment, in addition to the pure wire reliability, the reliability of the mold is also positively influenced by the insulation layer. Due to the thermally insulating sheathing, the mold temperature in the vicinity of the wire is lower and the wire does not represent a nucleus for mold cracks due to the lack of a rigid connection between the wire and the mold material for example a first 200 end for contacting the contact surface 120 of the printed circuit board 125, a second end 205 for contacting the contact surface 130 of the semiconductor element 135 and an intermediate section 210 arranged between the first end 200 and the second end 205. The insulating layer 115 is exclusive in this exemplary embodiment arranged in the intermediate section 210 and the ends 200, 205 freed from the insulation layer 115, which can also be referred to as bonding feet, are welded to the contact surfaces 120, 130 by means of so-called ultrasonic wedge-wedge bonding, just by way of example. Lengths of the ends 200, 205 as sections of the conductor element 110 not surrounded by the insulating layer 115 are adapted, for example, to the dimensions of contact points between the ends 200, 205 and the contact surfaces 120, 135. For example, the ends 200, 205 have lengths of less than 1mm or less than 0.5mm.

In this exemplary embodiment, a length of the bond is equal to the previous figure rahts 105 smaller than 1, 5 times the distance 140 between the contact surface 120 of the circuit board 125 and the contact surface 130 of the semiconductor element 135. The bonding wire 105 has a bond loop whose height 145 is less than the height 155 of the other bonding wire 150, the has no insulation layer.

3 shows a flowchart of a method 300 for producing a bonding wire according to an embodiment. The method 300 includes a step 305 of providing an electrically conductive conductor element, which is a copper wire only by way of example, and a step 310 of encasing the conductor element with an electrically non-conductive insulation layer in order to produce the bonding wire. In this exemplary embodiment, the conductor element is sheathed with a silicon layer that is movable in relation to the conductor element, merely by way of example. In addition, the method 300 in this exemplary embodiment has a step 315 of removing part of the insulation layer in order to be able to connect the bonding wire to at least one contact area at the ends that are no longer insulated.

4 FIG. 4 shows a flow diagram of a method 400 for manufacturing a circuit according to an embodiment. The method 400 includes a step 405 of providing a printed circuit board and a semiconductor element and a step 410 of arranging the semiconductor element on the printed circuit board.

This is followed by a step 415 of connecting the semiconductor element to the printed circuit board by a bonding wire using a bonding method.

As described with reference to the previous figures, the bonding wire used here includes a conductor element for electrically conductively connecting a contact surface of a printed circuit board to a contact surface of a semiconductor element, the conductor element being encased by an electrically non-conductive insulation layer.

According to one exemplary embodiment, step 415 is repeated several times in order to electrically conductively connect a plurality of contact surface pairs using a plurality of bonding wires of corresponding design. Contact surface pairs located directly on the printed circuit board can also be connected. According to one exemplary embodiment, the lengths of the bonding wires used are adapted to the distances between the contact surfaces to be connected in each case. In this way, the curvatures of the individual bonding wires can be kept as small as possible. The distances between the respective contact surfaces to be connected can be taken from a circuit layout, for example, so that the lengths of the bonding wires to be used can be easily determined.

Reference List

100

circuit

105

bonding wire

110

ladder element

115

insulation layer

120

contact surface of the circuit board

125

circuit board

130

Contact surface of the semiconductor element

135

semiconductor element

140

Distance between the contact surfaces

145

height of the bonding wire

150

different bonding wire

155

Height of the other bonding wire

160

further contact surface of the circuit board

200

First end of the bond wire

205

Second end of the bond wire

210

Intermediate section of the bond wire

300

Method for producing a bonding wire

305

Step of providing a conductor element

310

Coating step

315

step of removal

400

Method of making a circuit

405

Step of providing a circuit board and a semiconductor element

410

arranging step

415

step of connecting

Claims (12)

Bonding wire (105) with a conductor element (110) for the electrically conductive connection of a contact surface (120) of a printed circuit board (125) with a contact surface (130) of a semiconductor element (135), characterized in that the conductor element (110) has an electrically non- conductive insulation layer (115) is coated. Bond wire (105) according to claim 1 , wherein the insulation layer (115) is formed as a cohesive lacquer layer. Bond wire (105) according to claim 1 , wherein the insulating layer (115) and the conductor element (110) are movable relative to each other Bonding wire (105) according to one of the preceding claims, wherein the bonding wire (105) is formed with aluminum and/or copper. Bonding wire (105) according to one of the preceding claims, wherein the bonding wire (105) and/or the conductor element (110) has a diameter of 10 µm to 500 µm. Bonding wire (105) according to any one of the preceding claims, wherein the insulating layer (115) is thermally insulating. Bonding wire (105) according to one of the preceding claims, wherein the bonding wire (105) has a first end (200) for contacting the contact area (120) of the printed circuit board (125), a second end (205) for contacting the contact area (130) of the semiconductor element (135) and an intermediate section (210) arranged between the first end (200) and the second end (205), the insulating layer (115) being arranged exclusively in the intermediate section (210). Circuit (100) with a printed circuit board (125) and a semiconductor element (135), characterized in that a contact surface (120) of the printed circuit board (125) and a contact surface (130) of the semiconductor element (135) and/or the contact surface (120) the printed circuit board (125) and a further contact surface (160) of the printed circuit board (125) are electrically conductively connected to one another by a bonding wire (105) according to one of the preceding claims. Circuit (100) according to claim 8 , wherein a length of the bonding wire (105) is less than 1.5 times the distance (140) between the contact surface (120) of the printed circuit board (125) and the contact surface (130) of the semiconductor element (135). Method (300) for producing a bonding wire (105) according to one of the preceding ones Claims 1 until 7 , wherein the method (300) comprises the following steps (305, 310): providing (305) an electrically conductive conductor element (110); and sheathing (310) the conductor element (110) with an electrically non-conductive insulation layer (115) in order to produce the bonding wire (105). Method (300) according to claim 10 , having a step (315) of removing part of the insulating layer (115) in order to be able to connect the bonding wire (105) to at least one contact area (120, 130, 160) in an electrically conductive manner. Method (400) for producing a circuit (100) according to one of Claims 8 or 9 , wherein the method (400) comprises the following steps (405, 410, 415): providing (405) a circuit board (125) and a semiconductor element (135); arranging (410) the semiconductor element (135) on the circuit board (125); and connecting (415) the semiconductor element (135) to the printed circuit board (125) by a bonding wire (105) according to one of Claims 1 until 7 using a bonding process.

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