Method for manufacturing circuit board, circuit board and power module

Abstract

A method for manufacturing a circuit board, comprising: a step for preparing a plurality of composites provided with a silicon nitride plate, a copper plate, and a brazing layer for bonding the silicon nitride plate and the copper plate; and a step for preparing a laminate by disposing a spacer between the pair of composites. And a step for heating the laminate at a temperature of 370-420 DEG C for 3.5 hours or more to degrease the brazing layer. And a step for heating the laminated body so that the silicon nitride plate and the copper plate are joined via the brazing layer.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a circuit substrate, a circuit substrate, and a power module. Background Art

[0002] Circuit boards used in electronic devices are manufactured by joining a ceramic plate and a metal plate using a brazing material. During joining, a pressure fixture is used to secure the objects and apply pressure to promote the reaction between the brazing material and the ceramic plate. Patent Document 1 discloses a pressure fixture using a spring washer.

[0003] Existing technology

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 2022-106195 Summary of the Invention

[0006] Problems to be solved by the invention

[0007] When using a pressure fixture to join a ceramic plate and a metal plate, the pressure distribution deviates perpendicular to the direction of pressure. This causes a deviation in the reaction process between the brazing material and the ceramic plate, thereby reducing the bond strength. Therefore, the present disclosure provides a circuit substrate with high bond strength and a method for manufacturing the same. Furthermore, a power module incorporating such a circuit substrate is provided.

[0008] Means for solving problems

[0009] One embodiment of the present invention provides the following method for manufacturing a circuit board.

[0010] [1] A method for manufacturing a circuit substrate, comprising: a process of preparing a plurality of composite bodies, wherein the composite bodies include a silicon nitride plate, a copper plate, and a solder layer bonding the silicon nitride plate and the copper plate; a process of arranging a spacer between a pair of the composite bodies to prepare a laminate; a process of heating the laminate body at a temperature range of 370 to 420° C. for more than 3.5 hours to degrease the solder layer; and a process of heating the laminate body so that the silicon nitride plate and the copper plate are bonded via the solder layer.

[0011] The above-mentioned circuit board manufacturing method heats the laminate within a temperature range of 370-420°C for at least 3.5 hours. This effectively removes carbon from the organic binder in the solder layer and promotes the reaction between the solder layer and the silicon nitride plate. This ensures a sufficient and uniform reaction between the solder layer and the silicon nitride plate, without any unevenness. As a result, a circuit board with high bonding strength can be obtained.

[0012] The method for manufacturing a circuit board according to the above-mentioned [1] may be any one of the following [2] to [3].

[0013] [2] The method for manufacturing a circuit board according to [1], wherein, in the step of heating the laminate, heating is performed while the laminate is pressurized in a laminating direction using a pressure jig.

[0014] [3] The method for manufacturing a circuit board according to [1] or [2], wherein the solder layer contains Ag, Cu, TiH2 and Sn.

[0015] In the method for manufacturing a circuit substrate of the above-mentioned [2], a pressure fixture is used to further pressurize the composite. This can further promote the reaction between the solder layer and the silicon nitride plate, resulting in a circuit substrate with higher bonding strength. In the method for manufacturing a circuit substrate of the above-mentioned [3], the solder layer contains Ag, Cu, TiH2, and Sn. Due to the solder layer having such a composition, a titanium nitride layer is easily formed between the silicon nitride plate and the solder layer during heating. Therefore, a circuit substrate with higher bonding strength can be obtained.

[0016] One embodiment of the present disclosure provides the following circuit substrate.

[0017] [4] A circuit substrate comprising a silicon nitride plate, a copper plate, and a bonding layer bonding the silicon nitride plate and the copper plate, wherein the bonding layer comprises, starting from one side of the silicon nitride plate, a first bonding layer containing titanium nitride, a second bonding layer containing Si, and a third bonding layer containing Ag, wherein the carbon content in the first bonding layer is C1 atomic %, the carbon content in the third bonding layer is C3 atomic %, and the average value of C1 / C3 is less than 0.5.

[0018] Since the average value of C1 / C3 in the circuit substrate of [4] is 0.5 or less, carbon from the binder in the first bonding layer can be fully removed. In such a circuit substrate, the first bonding layer, the second bonding layer, and the third bonding layer are fully formed. Therefore, the bonding strength between the silicon nitride plate and the copper plate can be improved.

[0019] The method for manufacturing a circuit board according to the above-mentioned [4] may be any one of the following [5] to [7].

[0020] [5] The circuit substrate according to [4], wherein the difference between the maximum and minimum thickness values ​​of the first bonding layer is 70 nm or less.

[0021] [6] The circuit substrate according to [4] or [5], wherein the thickness of the second bonding layer is 50 nm or more.

[0022] [7] The circuit substrate according to any one of [4] to [6], wherein the average thickness of the first bonding layer is t1, the average thickness of the second bonding layer is t2, and t1 / t2 is less than 5.

[0023] The difference between the maximum and minimum thicknesses of the first bonding layer of the circuit substrate of the above-mentioned [5] is 70 nm or less. In a circuit substrate having a first bonding layer of such thickness, the first bonding layer is fully formed over a large range without causing deviation. Therefore, the bonding strength between the silicon nitride plate and the copper plate can be fully improved. The thickness of the second bonding layer of the circuit substrate of the above-mentioned [6] is 50 nm or more. In such a circuit substrate, since a sufficiently thick second bonding layer is formed, the bonding strength between the silicon nitride plate and the copper plate can be fully improved.

[0024] In the circuit substrate of [7], the average thickness of the first bonding layer is t1, and the average thickness of the second bonding layer is t2, so t1 / t2 is less than 5. In a circuit substrate where the average thickness of the first bonding layer and the average thickness of the second bonding layer are within this range, the first bonding layer and the second bonding layer are formed very evenly. Therefore, the bonding strength between the silicon nitride plate and the copper plate can be sufficiently improved.

[0025] One embodiment of the present disclosure provides the following power module.

[0026] [8] A power module comprising the circuit substrate described in any one of [4] to [7] above, and a semiconductor element electrically connected to the copper plate of the circuit substrate.

[0027] In the power module, the bonding strength between the silicon nitride plate and the copper plate of the circuit board is high, so the power module has excellent durability.

[0028] Effects of the Invention

[0029] The present disclosure can provide a circuit substrate having high bonding strength and a method for manufacturing the same, and can also provide a power module having such a circuit substrate. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 is a cross-sectional view of the composite.

[0031] Figure 2 This is an example of a cross-sectional view of a laminate for explaining the steps in the method for manufacturing a circuit board.

[0032] Figure 3 It is a perspective view showing a pressure jig.

[0033] Figure 4It is a plan view showing a structure with a portion of the press jig cut away.

[0034] Figure 5 It is a front view showing the structure with a portion of the press jig cut away.

[0035] Figure 6 It is a side view showing a structure with a portion of the press jig cut away.

[0036] Figure 7 Yes Figure 4 VII-VII line cross-sectional view of the structure shown in .

[0037] Figure 8 This is a cross-sectional view of the structure showing a state in which the pressure plate is raised to restore the spring washer.

[0038] Figure 9 It is an enlarged representation Figure 8 A cross-sectional view of a composite and a portion of a spacer.

[0039] Figure 10 It is a cross-sectional view showing a circuit board.

[0040] Figure 11 (A) is a STEM image showing a cross section of a circuit board in Example 1. (B) is a STEM image showing a cross section of a circuit board in Comparative Example 1.

[0041] Figure 12 (A) is a graph showing the distribution of titanium elements in the cross section of Example 1 as determined by EDX analysis. (B) is a graph showing the distribution of silicon elements in the cross section of Example 1 as determined by EDX analysis.

[0042] Figure 13 (A) is a graph showing the distribution of silver elements in the cross section of Example 1 as determined by EDX analysis. (B) is a graph showing the distribution of copper elements in the cross section of Example 1 as determined by EDX analysis.

[0043] Figure 14 (A) is a graph showing the distribution of titanium in the cross section of the circuit substrate of Comparative Example 1 as determined by EDX analysis. (B) is a graph showing the distribution of silicon in the cross section of the circuit substrate of Comparative Example 1 as determined by EDX analysis.

[0044] Figure 15 (A) is a graph showing the distribution of silver elements in the cross section of the circuit board of Comparative Example 1 as determined by EDX analysis. (B) is a graph showing the distribution of copper elements in the cross section of the circuit board of Comparative Example 1 as determined by EDX analysis.

[0045] Figure 16 This is an EDX line section showing Example 1.

[0046] Figure 17 (A) is a photograph showing the state at the time of peeling the copper plate from the circuit board in Example 1. (B) is a photograph showing the state at the time of peeling the copper plate from the circuit board in Comparative Example 1.

[0047] Figure 18 (A) is an SEM image showing the peeling surface at the time of peeling the copper plate from the circuit board in Example 1. (B) is an SEM image showing the peeling surface after peeling the copper plate from the circuit board in Comparative Example 1.

[0048] Figure 19 (A) is a distribution chart showing the distribution of silicon element in the peeling surface at the time of peeling the copper plate from the circuit board in Example 1 by EDX analysis. (B) is a distribution chart showing the distribution of silicon element in the peeling surface after peeling the copper plate from the circuit board in Comparative Example 1 by EDX analysis. DETAILED DESCRIPTION

[0049] Hereinafter, an embodiment of the present disclosure will be described. However, the following embodiment is an example to explain the present disclosure, and is not intended to limit the present disclosure to the following. The upper limit or lower limit of the numerical range disclosed in the present disclosure can be replaced with any one of the values shown in the examples. In addition, the upper limit values and lower limit values listed separately can be combined arbitrarily. Unless otherwise specified, the materials or components exemplified in the present disclosure can be used singly or in combination of two or more. In the description, the same elements or elements having the same function are given the same reference numerals, and the repeated description is omitted. In addition, unless otherwise specified, the positional relationship of up, down, left, right, and the like used in the description is based on the positional relationship shown in the drawing.

[0050] Hereinafter, with reference to Figures 1 to 9 A manufacturing method of a circuit board relating to one embodiment will be described. The manufacturing method of the circuit board relating to the present embodiment includes: a step (a) of preparing a plurality of composite bodies 40 (see Figure 1 ), in which the composite body 40 has a silicon nitride plate 10, a copper plate 50, and a solder layer 30 bonding them; and a step (b) of arranging a spacer 70 between a pair of composite bodies 40 to prepare a laminate 80 (see Figure 2 ); and a step (c) of heating the laminate 80 to degrease the solder layer; and a step (d) of heating the laminate 80 to join the silicon nitride plate 10 and the copper plate 50 through the solder layer 30 to obtain a joined body; and a step (e) of preparing a circuit board from the joined body.

[0051] In step (a), silicon nitride plate 10 can be made from a silicon nitride sintered body formed by sintering silicon nitride powder. The shape of silicon nitride plate 10 is not particularly limited, as long as it is plate-like. For example, the thickness of silicon nitride plate 10 can be 0.2 to 2 mm, or 0.32 to 1.1 mm.

[0052] The shape of the copper plate 50 is not particularly limited as long as it can be bonded to the main surface of the silicon nitride plate 10. For example, the thickness of the copper plate 50 may be 0.1 to 1.2 mm, or 0.2 to 1.0 mm. The surface of the copper plate 50 may have a plating film.

[0053] Separation lines can be formed on the main surface of the silicon nitride plate 10. For example, a laser beam can be irradiated onto the main surface of the silicon nitride plate 10 to form scribe lines serving as the separation lines. Examples of the irradiated laser beam include laser beams emitted by a CO2 laser and a YAG laser. By intermittently irradiating the main surface with a laser beam emitted by such a laser source, scribe lines serving as separation lines are formed. Such separation lines can be used as cutting lines when separating the bonded body.

[0054] The brazing material applied to the main surface of the silicon nitride plate 10 may contain, for example, silver, copper, tin, active metals, metal compounds containing these elements, an organic solvent, and an organic binder. The viscosity of the brazing material may be, for example, 5 to 20 Pa·s. The organic solvent content in the brazing material may be, for example, 5 to 25% by mass, and the organic binder content may be, for example, 2 to 15% by mass.

[0055] The brazing material may contain silver in the form of a metal element or a metal compound (alloy). In addition to silver, it may also contain one or more metals selected from the group consisting of copper, tin and active metals. The two or more metals may form an alloy. The active metal may contain one or more metals selected from the group consisting of titanium, hafnium, zirconium and niobium. The silver content in the brazing material, converted to Ag, may be 45 to 95% by mass, or 50 to 95% by mass. The total content of silver and copper in the brazing material, converted to Ag and Cu, respectively, may be 65 to 100% by mass, 70 to 99% by mass, or 90 to 98% by mass.

[0056] The active metal content in the brazing material can be 0.5 to 8 parts by mass per 100 parts by mass of Ag and Cu combined. Setting the active metal content to 0.5 parts by mass or greater improves the bondability between the silicon nitride plate and the brazing material. On the other hand, setting the active metal content to 8 parts by mass or less prevents the formation of a brittle alloy layer at the joint interface.

[0057] The above-mentioned metals contained in the brazing material can be contained in the form of nitrides, oxides, carbides, or hydrides. As an example, the brazing material can contain titanium nitride and / or titanium hydride (TiH2). This can significantly improve the bonding strength between the silicon nitride plate 10 and the copper plate 50. The TiH2 content can be 1 to 8 parts by mass per 100 parts by mass of Ag and Cu combined.

[0058] The tin content in the brazing material can be 0.5 to 6 parts by mass relative to 100 parts by mass of the total of Ag and Cu. Setting the tin content to 0.5 parts by mass or greater improves the bondability between the silicon nitride plate 10 and the brazing material. On the other hand, setting the tin content to 5 parts by mass or less prevents the formation of a brittle alloy layer at the bonding interface.

[0059] A brazing material can be applied to the main surface of the silicon nitride plate 10 by a roll coating method, screen printing method, transfer method, or the like, and then dried to form one or more brazing layers 30. The brazing layer 30 can contain, for example, Ag, Cu, TiH2, and Sn. The brazing layer 30 can be provided at the location where the copper plate 50 and the silicon nitride plate 10 are joined. After forming the brazing layer 30, the silicon nitride plate 10 and the copper plate 50 are laminated with the brazing layer 30 interposed therebetween to produce a plurality of composite bodies 40.

[0060] In step (b), if Figure 2 As shown, the composite 40 and the spacer 70 are laminated together adjacent to each other in the lamination direction to prepare a laminate 80. A commercially available carbon plate can be used as the spacer 70. The density of the carbon plate can be 1.6 to 1.9 g / cm3. The thickness of the carbon plate can be 0.5 to 1.0 mm. The surface roughness Ra can be 5 to 10 μm. The spacer 70 and the composite 40 can be repeatedly laminated in any number to form a laminate 80. There is no particular limitation on the number of laminated composites 40 and spacers 70, and they can be adjusted according to the size of the heating furnace used. By laminating in this way, a plurality of composites 40 can be heated at one time, so that a joint body can be prepared efficiently.

[0061] The laminate 80 may be heated while being pressed in the lamination direction. Figure 3 、 4 , 5, 6, 7 and 8 describe an example of a method of pressurizing the laminate 80. Figure 3The structure 90 includes a pressure jig 1 and a laminate 80 sandwiched between a base plate 2 and a cover plate 3 of the pressure jig 1. The laminate 80 is composed of a plurality of spacers 70 and a plurality of composites 40 alternately stacked. The laminate 80 is rectangular in plan view, but may also have other shapes. The spacer 70 is arranged between the laminate 80 and the pressure jig 1. The spacer 70 also has the function of preventing the composites 40 from joining to each other and the composites 40 from joining to the pressure jig 1.

[0062] like Figure 3 As shown, the pressure jig 1 includes a plate-shaped bottom plate 2 (base portion) on which a laminate 80 is placed, and a cover plate 3 (cover portion) disposed opposite the bottom plate 2. The cover plate 3 and the bottom plate 2 sandwich the laminate 80. Furthermore, the pressure jig 1 includes a plurality of spring washers 4 disposed on the cover plate 3, and a pressure plate 5 (pressing portion) disposed on the spring washers 4. Furthermore, the pressure jig 1 includes a pressurizing structure 6 that compresses the spring washers 4 via the pressure plate 5, thereby pressurizing the laminate 80.

[0063] The base plate 2 is, for example, rectangular in shape and has a protruding area 2a extending from the laminate 80 in a plan view, that is, an area not overlapping the laminate 80. Multiple (e.g., two) pillars 8 (pillar members) are vertically disposed on the protruding area 2a of the base plate 2 along the short sides of the base plate 2. The pillars 8 are arranged on opposite sides of the base plate 2 in the longitudinal direction (left-right direction), with the laminate 80 positioned between the pair of opposing pillars 8. Engaging holes 8a are formed in the upper portions of the pillars 8, into which engaging claws 9 are inserted.

[0064] like Figure 5 and 7 As shown, the cover plate 3 is rectangular in shape, corresponding to the shape of the laminate 80, and has a surface 3a (hereinafter referred to as the "lower surface") and another surface 3b (hereinafter referred to as the "upper surface"). The lower surface 3a is a flat surface that contacts the spacer 70 disposed near the cover plate 3. Figure 3 As shown, a plurality of countersunk holes 3c are formed on the upper surface 3b, each receiving a spring washer 4. The depth of each countersunk hole 3c can be, for example, such that the entire spring washer 4 can be accommodated when the spiral spring washer 4 is compressed to a flat state. The countersunk holes 3c are annular in plan view and accommodate the annular spring washer 4, thereby preventing the spring washer 4 from shifting. The countersunk holes 3c serve as positioning members for the spring washer 4.

[0065] like Figure 5 As shown, the pressing plate 5 has a remaining area 5a opposite to the protruding area 2a of the bottom plate 2 in a plan view. Figure 3 and Figure 4As shown, the remaining area 5a is formed with a support through-hole 5b for the support 8 to pass through. The upper surface of the remaining area 5a is provided with a receiving groove 5c that penetrates the support through-hole 5b. The locking claw 9 is accommodated in the receiving groove 5c.

[0066] The pressure plate 5 is arranged in an overlapping manner with the cover plate 3, and is further pressed downward to abut against the spring washer 4. When the pressure plate 5 is pressed downward, the pillar 8 passes through the pillar through-hole 5b provided on the remaining area 5a of the pressure plate 5. The upper part of the pillar 8 protrudes above the pillar through-hole 5b. A locking hole 8a is provided on the upper part of the pillar 8, and a locking claw 9 (locking component) is inserted and passed through the locking hole 8a. The locking claw 9 passes through the locking hole 8a horizontally and abuts against the surface (upper surface) on the opposite side of the side surface (lower surface) of the pressure plate 5 that abuts against the spring washer 4, thereby locking the pressure plate 5. A receiving groove 5c corresponding to the outer shape of the locking claw 9 is formed on the upper surface of the pressure plate 5, and the locking claw 9 slides along the receiving groove 5c.

[0067] When the locking claws 9 engage the pressure plate 5, the pressure plate 5 is restricted from upward movement. By restricting the movement of the pressure plate 5, the spring washer 4 is prevented from returning to its original position, maintaining the spring washer 4 in a compressed state. The pressure structure 6 of this embodiment includes at least the pressure plate 5, the support column 8, the engagement hole 8a, and the locking claws 9.

[0068] The spring washer 4 is formed of, for example, an alloy such as Inconel 750 or Inconel 718, silicon nitride, or a carbon composite. The spring washer 4 is in a non-compressed state when it is not in contact with the cover plate 3 (see FIG. Figure 8 ). The spring washer 4 is an example of a compression spring, which is wound in a spiral shape without overlapping, and whose two end portions 4a, 4b are spaced apart. More specifically, the spring washer 4 is in a C-shape, with the two end portions 4a, 4b separated from each other, and offset in the axial direction (e.g., up and down directions) assuming a spiral shape. Here, in the countersunk hole 3c of the cover plate 3, one end portion abutting against the bottom of the countersunk hole 3c is referred to as the lower end portion 4a, and the other end portion on the opposite side is referred to as the upper end portion 4b. When the spring washer 4 is compressed by the pressurizing structure 6 through the cover plate 3, the lower end portion 4a and the upper end portion 4b approach each other, and the spiral shape of the spring washer 4 is released, presenting an almost flat shape (see Figure 7 ).

[0069] The multiple spring washers 4 are arranged so as not to extend beyond the outer edge 3x of the cover plate 3 but rather to be contained within the outer edge 3x of the cover plate 3. Furthermore, multiple spring washers 4 are arranged along the outer edge 3x of the cover plate 3. For example, the outer edge 3x of the cover plate 3 in this embodiment is rectangular. Three spring washers 4 are arranged side by side along each short side of the outer edge 3x, and five spring washers 4 are arranged side by side along each long side of the outer edge 3x. By arranging multiple spring washers 4 along the outer edge 3x of the cover plate 3, it is easier to uniformly pressurize the laminate 80 through the cover plate 3.

[0070] A plurality of spring washers 4 are arranged at equal intervals. Specifically, a total of 15 spring washers 4 are arranged in 3 rows and 5 columns (multiple rows and columns), and all spring washers 4 are arranged at equal intervals. By arranging the spring washers 4 at equal intervals, it is easier for the cover plate 3 to uniformly pressurize the laminate 80. In addition, the plurality of spring washers 4 arranged only along the outer edge 3x of the cover plate 3 can be arranged at equal intervals. In addition, when the center of the cover plate 3 is limited in a plan view, the plurality of spring washers 4 can be arranged point-symmetrically with respect to the center.

[0071] A separation region 4x is formed between the lower end 4a and the upper end 4b of the spring washer 4 (between the two ends). The multiple spring washers 4 are arranged so that the separation region 4x faces the outer edge 3x of the cover plate 3. In other words, assuming that the spring washer 4 is annular in plan view, the spring washer 4 is arranged so that the separation region 4x is closer to the outer edge 3x of the cover plate 3 than the center point of the annular shape. Furthermore, assuming that a line connects the separation regions 4x of the multiple spring washers 4, the line is arranged along the outer edge 3x of the cover plate 3.

[0072] When the spring washer 4 is compressed, the spring washer 4 exerts the greatest repulsive force (pressure) at the lower end 4a and upper end 4b, which face each other across the separation region 4x. By arranging this separation region 4x so as to face the outer edge 3x of the cover plate 3, it is easier to reliably press the portion along the outer edge 3x of the cover plate 3, and it is easier to uniformly pressurize the laminate 80 via the cover plate 3.

[0073] Figure 9 The enlarged view shows the Figure 8 A portion of a cross section in the lamination direction of a laminated structure of the composite body 40 and the spacer 70. Figure 9In this embodiment, the cover plate 3 is laminated on the base plate 2 in the order of the spacer 70, the laminate 80, and the spacer 70. The laminate 80 is formed by laminating a pair of the composite 40 with the spacer 70 interposed therebetween. The composite 40 is formed by laminating a pair of the copper plate 50 with the silicon nitride plate 10 interposed therebetween via the brazing layer 30. The laminate 80 can be formed by repeating the lamination of any number of the composite 40 and the spacer 70. By using such a laminate structure, the reaction deviation of the laminate 80 at the time of heating and pressurization in the process (c) and the process (d) can be suppressed, and thus a bonded body having a high bonding strength can be obtained. Further, the number of the spacers 70 and the composites 40 constituting the laminate 80 is not particularly limited.

[0074] The process (c) is a process of degreasing carbon in the brazing layer 30. The heating temperature of the degreasing process can be 370 to 420°C, 380 to 415°C, or 390 to 410°C. Further, the heating time of the above heating temperature can be 3.5 hours or more, or 3.75 hours or more. Further, from the viewpoint of shortening the time required for the entire manufacturing process, the heating time can be 5 hours or less, or 4.5 hours or less. In the degreasing process, carbon contained in the brazing layer 30 from the organic binder can be reduced by thermal decomposition. During the heating in the process (d), the reaction between carbon and titanium can be suppressed, and the formation of titanium nitride and titanium silicide can be sufficiently performed.

[0075] The atmosphere in the heating furnace can be an inert gas such as nitrogen, and the process can be performed under reduced pressure lower than the atmospheric pressure or under vacuum. The heating furnace can be a continuous type for continuously manufacturing a plurality of the composites 40, or a batch type for manufacturing one or a plurality of the composites 40.

[0076] From the viewpoint of promoting the reaction, the heating temperature in the process (d) can be 700 to 900°C, or 750 to 850°C. The heating time can be 3 hours or less, or 2 hours or less. The pressure in the furnace during heating can be any one of the atmospheric pressure, the reduced pressure, or the vacuum. From the viewpoint of promoting the reaction, the pressure in the furnace can be 10"2to 10"7Pa.

[0077] The temperature increasing rate in the heating furnace in the process (c) and the process (d) can be 70 to 120°C / min, or 80 to 110°C / min. By setting the temperature increasing rate in this range, the time required for the entire manufacturing process can be sufficiently shortened. Further, the temperature decreasing rate after heating can also be in the same range as the above temperature increasing rate.

[0078] After step (d), an annealing step can be performed. The annealing temperature in the annealing step can be 400 to 650°C, or 500 to 600°C. The annealing time at the above annealing temperature can be 1.5 to 3.0 hours, or 2.0 to 2.5 hours. After cooling, the bonded body can be removed from the pressure fixture. By implementing the annealing step, the deformation of the laminate 80 caused by heating can be reduced, and a circuit substrate with sufficiently excellent thermal cycle characteristics can be prepared.

[0079] In step (e), the obtained bonded body is subjected to resist printing and etching to obtain a bonded body as shown in FIG. Figure 10 Circuit substrate 100 is shown. In circuit substrate 100, since the carbon in solder layer 30 has been fully removed, bonding layer 20 includes first bonding layer 21, second bonding layer 22, and third bonding layer 23. Therefore, the bonding strength between silicon nitride plate 10 and copper plate 50 in circuit substrate 100 can be substantially improved. Furthermore, the bonded product obtained in step (d) can be used directly as circuit substrate 100.

[0080] The circuit substrate 100 includes a pair of copper plates 50 on both surfaces of the silicon nitride plate 10 and a bonding layer 20 that bonds the respective main surfaces of the silicon nitride plate 10 to the main surfaces of the copper plates 50. The bonding layer 20 includes a first bonding layer 21, a second bonding layer 22, and a third bonding layer 23, in this order from the silicon nitride plate 10 side.

[0081] The shape of the circuit substrate 100 is not particularly limited, and it may be an aggregate substrate or a single-piece substrate obtained by dividing the aggregate substrate. The thickness of the circuit substrate may be 0.9 to 2.7 mm or 1.3 to 2.2 mm.

[0082] The bonding layer 20 comprises, in order from the silicon nitride plate 10 side, a first bonding layer 21 containing titanium nitride, a second bonding layer 22 containing Si, and a third bonding layer 23 containing Ag. Assuming the carbon content in the first bonding layer is C1 atomic % and the carbon content in the third bonding layer is C3 atomic %, the average C1 / C3 ratio is 0.5 or less. The circuit substrate 100 having such a bonding layer 20 can sufficiently reduce the carbon content in the first bonding layer 21 and improve the bonding strength between the silicon nitride plate 10 and the copper plate 50.

[0083] The bonding layer 20 includes a first bonding layer 21, a second bonding layer 22, and a third bonding layer 23. The bonding layer 20 contains titanium, silver, and silicon. The bonding layer 20 may further contain one or more metals selected from the group consisting of copper, tin, and an active metal. The two or more metals may be alloys. The active metal may contain one or more metals selected from the group consisting of titanium, hafnium, zirconium, and niobium.

[0084] The silver contained in the bonding layer 20 can be contained in the bonding layer 20 in the form of an alloy such as an Ag-Cu eutectic alloy. The silver content in the bonding layer 20 can be 60 to 95% by mass, calculated as Ag. The silver and copper contents in the bonding layer 20 can be 75 to 100% by mass, 85 to 99% by mass, or 90 to 98% by mass, calculated as Ag and Cu, respectively. This improves the density of the bonding layer 20 and substantially reduces residual stress in the bonding layer 20.

[0085] The active metal content in the bonding layer 20 can be 0.5 to 5 parts by mass relative to 100 parts by mass of the total of Ag and Cu. Setting the active metal content to 0.5 parts by mass or greater improves the bondability between the silicon nitride plate 10 and the bonding layer 20. On the other hand, setting the active metal content to 5 parts by mass or less prevents the formation of a brittle alloy layer at the bonding interface.

[0086] The metals contained in the bonding layer 20 may be contained in the form of nitrides, oxides, carbides, or hydrides. As an example, the bonding layer 20 may contain titanium nitride and / or titanium hydride (TiH2). This allows the silicon nitride plate 10 and the bonding layer 20 to react fully, thereby forming a first bonding layer 21, a second bonding layer 22, and a third bonding layer 23. This allows the bonding strength between the silicon nitride plate 10 and the copper plate 50 to be sufficiently improved. In the bonding layer 20, the content of TiH2 may be, for example, 1 to 8 parts by mass relative to a total of 100 parts by mass of Ag and Cu.

[0087] The elements contained in the bonding layer 20 can be identified and quantitatively analyzed by the following steps. First, a cross section of the circuit substrate is observed, for example, using a scanning transmission electron microscope (STEM). In the cross-sectional image, an energy dispersive X-ray analyzer (EDX) is used to analyze along a line perpendicular to the main surface of the silicon nitride plate 10 from the silicon nitride plate 10 to the copper plate 50 side. Thus, the distribution of each element can be detected in the form of a line profile and quantitatively analyzed. Here, the cross section of the present disclosure refers to a cross section perpendicular to the main surface of the silicon nitride plate 10 provided with the bonding layer 20 and passing through the bonding layer 20.

[0088] The first bonding layer 21 is a layer containing titanium nitride. The titanium nitride content can be 50 to 90 atomic percent, 55 to 85 atomic percent, or 60 to 80 atomic percent. The titanium and nitrogen elements detected in the first bonding layer 21 can be greater than those detected in the second bonding layer 22 and the third bonding layer 23. In other words, the titanium nitride content of the first bonding layer 21 can be higher than that of the second bonding layer 22 and the third bonding layer 23.

[0089] The titanium nitride phase contained in the first bonding layer 21 can be formed in a layered manner along the contact surface between the silicon nitride plate 10 and the first bonding layer 21. By forming the titanium nitride phase in a continuous layered manner on the contact surface between the silicon nitride plate 10 and the first bonding layer 21, the bonding strength between the silicon nitride plate 10 and the copper plate 50 can be further improved. The formation of the titanium nitride phase in a layered manner along the contact surface between the silicon nitride plate 10 and the first bonding layer 21 can be confirmed by analyzing a cross section using, for example, an electron probe microanalyzer (EPMA).

[0090] The thickness of the first bonding layer 21 can be determined by the length of the line where the detected titanium and nitrogen contents are 10 atomic % or more. The titanium and nitrogen contents in the first bonding layer 21 can be 10 to 45 atomic %, or 20 to 40 atomic %.

[0091] The thickness of the first bonding layer 21 can be 100nm to 300nm, or 150nm to 250nm. The difference between the maximum and minimum values ​​of the thickness of the first bonding layer 21 can be 70nm or less, 50nm or less, or 45nm or less. By making the difference between the maximum and minimum values ​​of the thickness of the first bonding layer 21 within this range, the first bonding layer 21 contains sufficient titanium nitride, thereby improving the bonding strength between the silicon nitride plate 10 and the copper plate 50. The average value t1 of the thickness of the first bonding layer 21 can be determined as the average value of the thickness measured on more than 5 lines. The average value t1 of the thickness of the first bonding layer 21 can be 175 to 235nm, 180 to 230nm, or 190 to 220nm.

[0092] The second bonding layer 22 is a layer containing Si. The Si originates from the silicon nitride plate 10. When the silicon nitride plate 10 and the copper plate 50 are heated and bonded via the brazing layer 30, it is believed that the heating causes the silicon nitride to react with the titanium in the brazing layer 30, forming a layer containing titanium silicide. This layer is the second bonding layer 22.

[0093] The Si content of the second bonding layer 22 can be 10 to 40 atomic percent, or 20 to 30 atomic percent. A second bonding layer 22 with a Si content within this range is formed by a sufficient reaction between the silicon nitride plate 10 and the titanium in the brazing layer 30. Consequently, the bonding strength between the silicon nitride plate 10 and the copper plate 50 can be sufficiently enhanced.

[0094] The second bonding layer 22 can be formed between the first bonding layer 21 and the third bonding layer 23 to perform isolation. That is, the second bonding layer 22 can be formed in the entire area between the first bonding layer 21 and the third bonding layer 23. Such a second bonding layer 22 is formed when the silicon nitride plate 10 and the copper plate 50 are heat-bonded by the solder layer 30, and the reaction of the silicon nitride with titanium in the solder layer 30 is sufficiently performed. Therefore, the bonding strength between the silicon nitride plate 10 and the copper plate 50 of the circuit substrate 100 can be improved.

[0095] The thickness of the second bonding layer 22 can be determined by the length of a line in which the content of detected Si is 10 atomic % or more. The thickness of the second bonding layer 22 can be 50 nm or more, can be 50 nm to 120 nm, can be 60 nm to 110 nm, or can be 80 nm to 100 nm. By making the thickness of the second bonding layer 22 in this range, the reaction of the silicon nitride with titanium in the bonding layer is sufficiently performed, and the bonding strength between the silicon nitride plate and the copper plate can be improved.

[0096] The average value t2 of the thickness of the second bonding layer 22 can be determined by the average value of the thickness measured on five or more lines. The average value t2 of the thickness of the second bonding layer 22 can be 60 nm to 100 nm, or can be 70 nm to 90 nm. The second bonding layer 22 in which the average value t2 of the thickness is in this range is formed by the reaction of the silicon nitride plate 10 and the solder layer 30. Such a second bonding layer 22 can sufficiently improve the bonding strength between the silicon nitride plate 10 and the copper plate 50.

[0097] The ratio (t1 / t2) of the average value t1 of the thickness of the first bonding layer 21 to the average value t2 of the thickness of the second bonding layer 22 can be 5 or less, can be 4 or less, or can be 3 or less. By making (t1 / t2) in this range, the first bonding layer 21 and the second bonding layer 22 can be formed in balance, and the bonding strength between the silicon nitride plate 10 and the copper plate 50 can be sufficiently improved. The lower limit of the above ratio can be 1.0, or can be 1.5.

[0098] The third bonding layer 23 is a layer containing Ag. The silver in the third bonding layer 23 can be 20 atomic % to 90 atomic %, or can be 30 atomic % to 80 atomic %. The thickness of the third bonding layer 23 can be 1.0 μm to 2.0 μm, or can be 1.2 μm to 1.7 μm.

[0099] The bonding layer 20 contains carbon from an organic binder, and the average value of the ratio (C1 / C3) of the carbon content (C1) contained in the first bonding layer 21 to the carbon content (C3) contained in the third bonding layer 23 is 0.5 or less. From the viewpoint of sufficiently reducing the carbon contained in the first bonding layer 21, the average value of (C1 / C3) can be 0.45 or less, or 0.4 or less. By making the average value of (C1 / C3) within this range, the thickness of the first bonding layer 21 can be made sufficiently large. As a result, the bonding strength between the silicon nitride plate 10 and the copper plate 50 can be sufficiently improved. The lower limit of the above ratio can be 0.2 or 0.3. The average value of (C1 / C3) is calculated as follows: (C3) and (C1) are measured on 5 or more lines, and (C1 / C3) is calculated based on each measured value. The above average value is obtained based on the values ​​of 5 or more (C1 / C3). Furthermore, each of the five or more values ​​of (C1 / C3) may be 0.5 or less, 0.45 or less, or 0.4 or less.

[0100] The bond strength between the silicon nitride plate 10 and the copper plate 50 can be measured in accordance with JIS K 6854-1:1999, "Adhesives - Peel Bond Strength Test Method," by peeling the copper plate 50 from the circuit substrate 100 at a 90° vertical angle and measuring the strength at the time of peeling. The bond strength can be 500-800 N / cm, or even 600-700 N / cm or higher. A circuit substrate 100 having such a bond strength can suppress variations in bond strength across the circuit substrate 100 and stabilize the quality of the circuit substrate 100.

[0101] The circuit substrate 100 can be used to manufacture a power module. The power module can be manufactured by mounting semiconductor elements electrically connected by soldering, wire bonding, etc. on a copper plate of the circuit substrate, then housing the circuit substrate and semiconductor elements in a housing and encapsulating them with resin.

[0102] While the embodiments of the present disclosure have been described above, the present disclosure is not limited to these embodiments. For example, the metal plates bonded to the pair of main surfaces of the silicon nitride plate, as well as the structure and shape of the bonding portion, may vary. Furthermore, a circuit substrate may be provided with a bonding layer and a copper plate only on one main surface of the silicon nitride plate.

[0103] Example

[0104] Hereinafter, the contents of the present disclosure will be described in more detail with reference to examples, but the present disclosure is not limited to the following examples.

[0105] (Example 1)

[0106] [Preparation of circuit substrate]

[0107] A silicon nitride plate having a thickness of 0.32 mm, a copper plate (dimensions: length×width×thickness=170 mm×120 mm×0.8 mm), and a brazing material were prepared. The copper plate was obtained by stamping.

[0108] The brazing material contains Ag, Cu, TiH2, and Sn. The mass ratio of Ag to Cu is 9:1. The brazing material contains 5 parts by mass of Sn and 3.5 parts by mass of TiH2 per 100 parts by mass of the total of Ag and Cu.

[0109] A brazing material was applied to the main surface of the silicon nitride plate by screen printing (mesh count: 150) and dried to form a brazing layer. The brazing layer was applied over an area equal to the main surface of the copper plate bonded to the silicon nitride plate. The thickness of the applied brazing layer was 0.03 mm.

[0110] After forming the brazing layer, the copper plate was stacked on the silicon nitride plate with the brazing layer in contact with the main surface of the copper plate to produce a composite. In this way, 20 composites of silicon nitride plates, brazing layers, and copper plates were prepared.

[0111] A pair of carbon plates (thickness: 0.5 mm, density: 1.8 g / cm 3 ) are respectively arranged between adjacent composite bodies, thereby preparing a laminate. Figure 9 As shown, spacers are arranged on both major surfaces of the laminate and fixed by a pressure jig.

[0112] In a state fixed by the press jig, the laminate fixed by the press jig is placed in a vacuum (10 -3 Pa) was heated to 400°C at a heating rate of 100°C / min and degreased at 400°C for 3.5 hours. - 3 In an atmosphere of Pa, the temperature was raised from 400°C to 750°C at a heating rate of 100°C / min, and heated at 750°C for 3 hours. Then, the temperature was lowered to 600°C at a cooling rate of 100°C / min, and maintained at 600°C for 2 hours to perform an annealing process. After cooling, the joint body was removed from the pressure fixture. In this way, a joint body in which a silicon nitride plate and a copper plate were joined by a joining layer was prepared. A portion of the copper plate in the prepared joint body was removed by etching to prepare a circuit substrate. In this way, the circuit substrate of Example 1 was obtained.

[0113] (Comparative Example 1)

[0114] A circuit board was prepared by the same procedure as in Example 1 except that degreasing was performed at 350° C. for 3 hours.

[0115] [Evaluation of circuit boards]

[0116] <Element Mapping of Layer State in Cross Section of Circuit Board>

[0117] The cross section of the obtained circuit substrate in the thickness direction was observed at a magnification of 25,000 times using a scanning transmission electron microscope (STEM, manufactured by Hitachi High-Technologies Corporation, product name: HD-2700). The element mapping of Ti, Si, Ag, and Cu was performed on the observed cross section using an energy dispersive X-ray analyzer (EDX, manufactured by Oxford, product name: XMAXN 100TLE) at an accelerating voltage of 200 kV. The STEM image of Example 1 is shown in FIG. Figure 11 As shown in (A), the element mapping results are as follows Figure 12 (A), 12(B), 13(A) and 13(B). The STEM images of Comparative Example 1 are shown in FIG. Figure 11 As shown in (B), the element mapping results are as follows Figure 14 (A), 14(B), 15(A) and 15(B). Figure 12 (A) and Figure 14 (A) represents the distribution of titanium element, Figure 12 (B) and Figure 14 (B) shows the distribution of silicon. Figure 13 (A) and Figure 15 (A) represents the distribution of silver elements, Figure 13 (B) and Figure 15 (B) shows the distribution of copper elements.

[0118] The results of STEM images and elemental mapping show that in Example 1, the second bonding layer 22 is located between the first bonding layer 21 and the third bonding layer 23, and plays an isolating role (see Figure 12 (A), 12 (B) and 13 (A)). On the other hand, in Comparative Example 1, although the second bonding layer 22A was confirmed, unlike the second bonding layer 22, the second bonding layer 22A was a discontinuous layer, and there was a portion where the first bonding layer 21 and the third bonding layer 23 were in direct contact (see Figure 14 (A), 14(B) and 15(A)).

[0119] <Measurement of Thickness of First and Second Bonding Layers 21 and 22>

[0120] In the above STEM image, the line profile of each element was measured by EDX analysis along the line from the silicon nitride plate to the copper plate. The EDX analysis results in Example 1 are as follows: Figure 16 As shown. Figure 16, the length of the line where the detected titanium element and nitrogen element are respectively more than 10 atomic % is taken as the thickness of the first bonding layer 21. In addition, the length of the line where the detected titanium element and silicon element are respectively more than 10 atomic % is taken as the thickness of the second bonding layer 22. Line profile analysis is performed at any 5 positions in the STEM image, and the thicknesses of the first bonding layer 21 and the second bonding layer 22 are measured in the same way. In Comparative Example 1, any 5 positions are selected from the portion where the second bonding layer 22A is formed for measurement. The average value t1 of the thickness of the first bonding layer 21 and the average value t2 of the thickness of the second bonding layer at the 5 measured positions are calculated, and t1 / t2 is calculated. The measurement results are shown in Table 1. In addition, Table 1 also shows the maximum value, minimum value and difference between the measured thicknesses of the bonding layers.

[0121] [Table 1]

[0122]

[0123] The results show that the thickness of the second bonding layer of Example 1 is greater than that of the second bonding layer of Comparative Example 1. Therefore, this indicates that heating causes the reaction of the silicon nitride plate and the solder layer to proceed fully. In addition, the second bonding layer in the circuit substrate of Example 1 has sufficient thickness, and the difference between the maximum and minimum values ​​is also sufficiently small. It can be confirmed by this result that heating causes the reaction height of the silicon nitride plate and the solder layer to proceed uniformly and fully.

[0124] <Ratio of C (Carbon) Contained in the First Joining Layer 21 and the Third Joining Layer 23>

[0125] In the above-mentioned line section, the portion where the silver element is detected to be 40 atomic % or more is used as the third bonding layer 23. Starting from the side of the silicon nitride plate 10, the measurement is carried out along the line at the position where the titanium element is initially detected to be 10 atomic % or more, and the atomic % of C (carbon) (C1) of the first bonding layer 21 at a distance of 100 nm from the copper plate 50 side is measured. In addition, starting from the above-mentioned initially detected position along the line, the atomic % of C (carbon) (C 3) of the third bonding layer 23 at a distance of 1000 nm from the copper plate 50 side is measured. Further, the ratio of C (carbon) (C1 / C3) is calculated based on each measured value. The determination of the atomic % of carbon is carried out by measuring the lines of 5 arbitrarily selected different positions. The results are shown in Table 2. In addition, Table 2 also shows the measured atomic % of carbon and the average value of the calculated (C1) / (C3), the maximum value, the minimum value, and the difference between the maximum value and the minimum value.

[0126] [Table 2]

[0127]

[0128] The amount of carbon detected in the first bonding layer relative to the third bonding layer in Example 1 was confirmed to be less than the amount of carbon detected in the first bonding layer relative to the third bonding layer in Comparative Example 1. This suggests that, in Example 1, the carbon from the binder in the first bonding layer was reduced by degreasing at a long time and high temperature. Therefore, it is believed that the reaction between carbon and titanium was suppressed, while the reaction between nitrogen from silicon nitride and titanium proceeded sufficiently.

[0129] <Copper Plate Bonding Strength and Bonding Condition>

[0130] In Example 1 and Comparative Example 1, the copper plate bonded to the silicon nitride plate was stretched vertically upward using a tensile tester, as shown in FIG. Figure 17 As shown in (A) and 17 (B), the bonding strength at the moment when the copper plate was peeled off from the silicon nitride plate was measured. The workbench of the tensile tester used was FGS-100VC produced by Nidec Shinpo Corporation. The dynamometer used was FGP-20 produced by Nidec Shinpo Corporation. The peeling was performed at a peeling speed of 50 mm / min. As a result, the value in Example 1 was 650 N / cm, and the value in Comparative Example 1 was 450 N / cm. Furthermore, SEM images of the peeled surface were observed, and elemental analysis of the fractured section was performed by EDX. The conditions for the elemental analysis were the same as those described above.

[0131] The appearance photo of the copper plate of Example 1 when peeling is as follows Figure 17 (A) The observation results of the SEM image of the peeling surface of Example 1 are as follows Figure 18 (A) is shown. The elemental analysis results of Example 1 by EDX are shown in Figure 19 (A) is shown. Similarly, the appearance photo of the copper plate of Comparative Example 1 when peeling is shown as follows Figure 17 (B) The observation results of the SEM image of the peeling surface of Comparative Example 1 are as follows Figure 18 (B) is shown. The elemental analysis results of Comparative Example 1 by EDX are shown as follows Figure 19 (B) shown. Figure 18 (A) and Figure 18 The black portion 101 in (B) indicates a portion containing silicon, and the gray portion 105 indicates a portion containing silver. Figure 19 (A) and Figure 19 Each dot of the dot pattern portion 102 in (B) represents a portion containing silicon, and the black portion 106 represents a portion containing silver.

[0132] from Figure 18As can be seen from Figures 18(A), 19(A), and 19(B), in Example 1, due to the large amount of silicon attached to the peeling surface, fracture occurred near the silicon nitride plate 10. In contrast, in Comparative Example 1, the amount of silicon attached to the peeling surface was less than that in Example 1, confirming that interfacial peeling occurred between the third bonding layer 23 and the copper plate 50. Example 1 had more silicon attached to the peeling surface than Comparative Example 1, and as mentioned above, the bonding strength was also higher. Based on these results, it can be seen that the circuit substrate of Example 1 has a more solid bond between the silicon nitride plate 10 and the bonding layer 20 than Comparative Example 1 because the first and second bonding layers are fully formed.

[0133] Industrial applicability

[0134] According to the present disclosure, a circuit substrate having high bonding strength and a method for manufacturing the same can be provided. In addition, a power module using such a circuit substrate is also provided.

[0135] Explanation of symbols

[0136] 1...Pressure fixture

[0137] 2...base plate

[0138] 3...Cover

[0139] 3x...outer edge

[0140] 4...Spring washer

[0141] 4a...lower end

[0142] 4b...upper end

[0143] 4x...Separation Area

[0144] 5...Pressure plate

[0145] 5b...pillar through hole

[0146] 6... Pressurized structure

[0147] 8...Pillar parts (pillars)

[0148] 9...Locking claw (locking part)

[0149] 8a...locking hole

[0150] 10...Silicon nitride board

[0151] 20...Joint layer

[0152] 21...First bonding layer

[0153] 22...Second bonding layer

[0154] 23...the third bonding layer

[0155] 50...copper coins

[0156] 30...Brazing layer

[0157] 40...complex

[0158] 70...spacer

[0159] 80...Laminate

[0160] 90...Structure

[0161] 100...Circuit board

[0162] 101, 106...black part

[0163] 102...dot pattern part

[0164] 105...Gray part

Claims

1. A method for manufacturing a circuit substrate, comprising: A process for preparing a plurality of composite bodies, wherein the composite bodies include a silicon nitride plate, a copper plate, and a brazing layer bonding the silicon nitride plate and the copper plate; and a step of disposing a spacer between a pair of the composite bodies to prepare a laminate; and heating the laminate at a temperature range of 370 to 420° C. for more than 3.5 hours to degrease the solder layer; and a step of heating the laminate to bond the silicon nitride plate and the copper plate via the brazing layer.

2. The method for manufacturing a circuit substrate according to claim 1, wherein: In the step of heating the laminate, heating is performed in a state where the laminate is pressurized in a laminating direction using a pressure jig.

3. The method for manufacturing a circuit substrate according to claim 1 or 2, wherein: The solder layer contains Ag, Cu, TiH2 and Sn.

4. A circuit substrate comprising a silicon nitride plate, a copper plate, and a bonding layer bonding the silicon nitride plate and the copper plate, wherein The bonding layer includes, starting from the silicon nitride plate side, a first bonding layer containing titanium nitride, a second bonding layer containing Si, and a third bonding layer containing Ag. Assuming that the carbon content in the first bonding layer is C1 atomic %, and the carbon content in the third bonding layer is C3 atomic %, the average value of C1 / C3 is less than or equal to 0.

5.

5. The circuit substrate according to claim 4, wherein The difference between the maximum and minimum thicknesses of the first bonding layer is 70 nm or less. The circuit substrate according to claim 4 , wherein: The second bonding layer has a thickness of 50 nm or more.

7. The circuit substrate according to claim 4, wherein: Assuming that the average thickness of the first bonding layer is t1 and the average thickness of the second bonding layer is t2, t1 / t2 is 5 or less. 8 . A power module comprising: the circuit substrate according to claim 4 ; and a semiconductor element electrically connected to the copper plate of the circuit substrate.

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