Semiconductor device module

Abstract

Semiconductor device module comprising: • a semiconductor device (T1, T11, D1, D11) comprising an upper electrode and a lower electrode; • a substrate (31) on which the lower electrode of the semiconductor device is contacted; • a heat sink (50) on which the substrate is mounted; • a conduction electrode (40, 41, 42) through which a main current of the semiconductor device flows; • an insulating housing (60) arranged to enclose the substrate; and • a holder (61 to 65, 611) which is arranged in a bar-like shape in the insulating housing, the holder supporting the lead electrode, • wherein one end of the lead electrode is brazed to the upper electrode of the semiconductor device (T1, T11, D1, D11), and another end side is inserted into a wall of the insulating housing, • the holder engages one end of the lead electrode to restrict movement of the lead electrode, and • a portion of the holder for supporting the lead electrode has a through-hole penetrating the holder in the thickness direction.

Description

Technical FieldThe present invention relates to a semiconductor device module, and more particularly, to a semiconductor device module including a power device.Prior ArtIn recent years, high-performance and downsized semiconductor device modules having high reliability have been desired as in-vehicle power semiconductor devices. To realize this, a direct line bonding (DLB) structure for directly bonding a power device to an external line electrode has been introduced. Moreover, a study has been made on a semiconductor device module having a direct cooling structure combined with a fin-mounted heat sink.When the direct cooling structure is used, a structure for packaging a plurality of power devices in a module is desired in order to simplify a sealing concept of a cooling unit and also a connection to an external wire.In the DLB structure, the reliability of the module is affected by the shape of a brazing metal for contacting a power device with a lead electrode, an amount of thermal displacement of the lead electrode, and adhesion of a sealing material to each component. Therefore, the shape of the brazing metal and the adhesion of the sealing material must be maintained in a good state to improve the reliability of the module.The manufacture of the high-performance semiconductor devices requires arranging a plurality of power devices in parallel while enlarging the individual power devices, thereby enlarging not only the lead electrodes but also the packages. Therefore, the challenge is to improve alignment accuracy of a lead electrode and a power device to obtain an advantageous shape of the brazing metal.As disclosed in Patent Document 1, for example, since the enlarged packages increase the cost of pressure-sealing with a molding resin, etc., a sealing structure for inserting one side of a lead electrode into a resin case and filling the resin case with an epoxy-based resin is regularly used. Here, the lead electrode is cantilevered. Thereby, the thermal displacement of the electrode due to the heat generated in, for example, a power device is likely to become larger. In addition, by not using the pressure sealing, it becomes difficult to reduce the thermal displacement of the lead electrode, whereby the load on the power device can be increased and the reliability of the semiconductor device module can be reduced.From JP 2015-133 462 A, it is known to provide a power module structure including: a ceramic substrate having a first conductor layer on a first main surface with a first edge remaining on the outer periphery and a second conductor layer on a second main surface with a second edge remaining on the outer periphery; a diode fixed to the second conductor layer of the ceramic substrate; a transistor provided with a control electrode and fixed to the second conductor layer of the ceramic substrate; a first terminal connected to the second conductor layer of the ceramic substrate; a second terminal for connecting the diode and the transistor to each other; a third terminal connected to the control electrode of the transistor with a wire; an insulating jumper fixed to the second terminal to hold the third terminal; a case that is connected to the ceramic substrate and that houses the diode, the transistor, the first terminal, the second terminal, the third terminal, and the bypass member; and a sealing resin member that is filled in the case.Prior Art DocumentsPatent DocumentsPatent Document 1: JP 2009-105 267 ASummaryProblem to be Solved by the InventionThe present invention has been devised to solve the problems, and an object is to provide a semiconductor device module having a DLB structure in which alignment accuracy of a lead electrode and a power device is improved and in which thermal displacement of the lead electrode is reduced.Means for Solving the ProblemThis object is achieved by the features of the independent claims. The dependent claims include advantageous further developments of the invention.Effects of the inventionIn the semiconductor device module according to the present invention, the holder restricts the movement of the lead electrode. As a result, the positional accuracy of the lead electrode is improved, and a distance between the lead electrode and the semiconductor device can be maintained appropriately. Further, a brazing metal for the lead electrode can be brazed while maintaining an advantageous shape, and thermal displacement of the brazing metal due to the generated heat when an electric current is applied to the semiconductor devices is reduced, whereby reliability of the semiconductor device module can be improved.Brief Description of the FiguresFIG. 1 is a plan view illustrating a configuration of a semiconductor device module 100 according to Embodiment 1. FIG. 2 is a cross-sectional view illustrating the configuration of the semiconductor device module 100 according to Embodiment 1. FIG. 3 is a cross-sectional view illustrating the configuration of the semiconductor device module 100 according to Embodiment 1 FIG. 4 is a cross-sectional view illustrating a configuration of a modification 1 of Embodiment 1. FIG. 5 is a cross-sectional view illustrating a configuration of a modification 2 of Embodiment 1. FIG. 6 is a cross-sectional view illustrating a configuration of a modification 3 of Embodiment 1. FIG. 7 is a plan view illustrating a configuration of a modification 4 of Embodiment 1. FIG. 8 is a plan view illustrating a configuration of a modification 5 of Embodiment 1. FIG. 9 is a plan view illustrating a configuration of a semiconductor device module 200 according to Embodiment 2.Description of Embodiment(s)< 1>FIG. 1 is a plan view illustrating a configuration of a semiconductor device module 100 according to Embodiment 1 of the present invention. The semiconductor device module illustrated in FIG. 1 is the one that packages power devices such as an insulated gate bipolar transistor (IGBT), a metal oxide semiconductor field effect transistor (MOSFET), and a free wheeling diode (FWD) as a module. FIG. 1 illustrates, as an example, a three-phase inverter.In FIG. 1, for example, the circuit patterns 30 and 301 are disposed on an insulating substrate 31 made of aluminum nitride (AlN), for example, inside a resin case 60 (insulating case). The switching devices T 1 and the diode devices D 1 are mounted on the circuit pattern 30, and the switching devices T 11 and the diode devices D 11 are mounted on the circuit pattern 301. The switching device T 1 and the diode device D 1 are each two parallel-connected devices, and the switching device T 11 and the diode device D 11 are also each two parallel-connected devices. Each of the switching devices T 1 and T 11 and each of the diode devices D 1 and D 11 has upper and lower electrodes.One end of a line electrode 40 is contacted with the upper electrodes of the switching devices T 1 and the diode devices D 1 by means of the direct line bonding. One end of a line electrode 41 is contacted with the upper electrodes of the switching devices T 11 and the diode devices D 11 by means of the direct line bonding.The other end side of the lead electrode 40 opposite to the direct lead contacted is insert-molded into a wall of the resin case 60. The other end is exposed on the upper surface of the resin case 60 to be connected to an external wire.The other end side of the lead electrode 41 opposite to the direct contacted side is insert molded into the wall of the resin case 60. The other end is exposed on the upper surface of the resin case 60 to be connected to an external wire. A lead electrode 42 is insert-molded in the wall of the resin case 60 so as to be parallel to the lead electrode 41. The other end is contacted on the circuit pattern 301 by means of the direct line contact. The main current of the inverter flows through the line electrodes 40 to 42.The described structure consists of a single phase of the three-phase inverter. The remaining two phases having the same configuration are disposed inside the resin case 60.The resin case 60 is divided by partitions 601 for respective accommodating portions of the phases of the inverter. In the regions divided by the partitions 601, holders 61 and 611 for supporting each of the ends of the lead electrodes 40 and 41 are arranged in a beam-like shape to cross regions from the wall of the resin case 60 to the partitions 601 and between the partitions 601.Next, the configuration of the holders 61 and 611 will be described with reference to FIGS. 2 and 3. FIG. 2 is a cross-sectional view illustrating a configuration of the cross section in FIG. 1 taken along a line A-A in the direction of the arrows. FIG. 3 is a cross-sectional view illustrating a configuration of the cross section in FIG. 1 taken along a line B-B in the direction of the arrows.As illustrated in FIG. 2, the insulating substrate 31 in the semiconductor device module 100 is contacted via a brazing metal 21, such as a solder, on a heat sink 50 made of a material having a higher thermal conductivity, for example, copper (Cu) or an alloy containing Al and Cu as main elements. The insulating substrate 31 is fixed by contacting a conductor pattern 32 disposed on the rear surface thereof with the brazing metal 21.The circuit patterns 30 and 301 are disposed on the front surface of the insulating substrate 31. The lower electrodes of the switching devices T 1 and the diode devices D 1 are contacted on the circuit pattern 30 via a brazing metal 20. The lower electrodes of the switching devices T 11 and the diode devices D 11 (FIG. 1 ) are contacted on the circuit pattern 301 via the brazing metal 20. The conductor patterns 30 and 301 are conductors made of, for example, Al or Cu, which are formed by plating the surface of the insulating substrate 31.The resin case 60 is mounted on the heat sink 50 to enclose the insulating substrate 31. The insert molded lead electrodes 40, 41, and 42 (FIG. 1 ) protrude from the inner surface of the resin case 60 to extend over the insulating substrate 31 in a cantilever manner.The lead electrode 41 whose other end side is inserted into the wall of the resin case 60 has the one end side which is contacted with the upper electrode of the switching devices T 11 and the diode devices D 11 (FIG. 1 ) by means of the direct lead bonding via a brazing metal 22, and whose tip is contacted with the circuit pattern 30 via a brazing metal 23.The tip of the lead electrode 41 engages with the holder 611. Thus, the line electrode 41 is contacted with the switching devices T 11 and the diode devices D 11 (FIG. 1 ), and its movement in the horizontal and vertical directions is restricted.The lead electrode 40 whose other end side is inserted into the wall of the resin case 60 has the one end side which is contacted with the upper electrode of the switching devices T 1 and the diode devices D 1 by the direct lead bonding via the brazing metal 22.The tip of the lead electrode 40 is engaged with the holder 61. Thus, the line electrode 40 is contacted with the switching devices T1 and the diode devices D1, and its movement in the horizontal and vertical directions is restricted.As illustrated in FIG. 3, the holder 61 has a recess in a portion in contact with the lead electrode 40 to be in contact not only with the upper surface but also with the side surfaces of the lead electrode 40, thereby more reliably restraining the movement of the lead electrode 40 in the horizontal direction. The holder 611 has the same structure.The holders 61 and 611 are integrally formed with the resin case 60 by using the same resin. When the semiconductor device module 100 is assembled, the resin case 60 is provided to cover the heat sink 50 on which the insulating substrate 31 and various semiconductor devices are mounted. Consequently, the holders 61 and 611 are in contact with the upper electrode of the various semiconductor devices (the switching devices T 1 and T 11 and the diode devices D 1 and D 11) via the brazing metal while supporting the tips of the lead electrodes 40 and 41.The portions of the holders 61 and 611 for respectively supporting the lead electrodes 40 and 41 have the through holes HL which penetrate the holders 61 and 611 in the thickness direction to enable checking whether the lead electrodes 40 and 41 are supported. The through holes HL may be replaced with notches or slits formed by cutting a part of the holders 61 and 611.After the resin case 60 is placed on the heat sink 50, the various semiconductor devices can be contacted with the lead electrodes 40 and 41, and the lead electrode 41 is contacted with the circuit pattern 30 by melting the brazing metals. This process may be performed simultaneously or separately with a process for brazing the various semiconductor devices to the insulating substrate 31.After the resin case 60 is placed on the heat sink 50, the various semiconductor devices are contacted with the lead electrodes 40 and 41, and the lead electrode 41 is contacted with the circuit pattern 30. Then, by filling the resin case 60 with a sealing material 70 made of silicone gel or epoxy-based resin, the structure including the holders 61 and 611 is sealed on the heat sink 50.As described above, the holders 61 and 611 support the tips of the lead electrodes 40 and 41 which are respectively arranged in a cantilever fashion. As a result, the positional accuracy of the lead electrodes 40 and 41 is improved, and the thermal displacement due to the heat generated when an electric current is applied to the semiconductor devices can be reduced. This can suitably maintain distances between the lead electrodes 40 and 41, the various semiconductor devices, and the circuit pattern 30, maintain brazing metals 22 and 23 having the advantageous shapes, and alleviate the stress applied to the semiconductor devices and the brazing metals by reducing the thermal displacement due to the heat generated when an electric current is applied to the semiconductor devices. As a result, the reliability of the semiconductor device module is improved.Although FIGS. 2 and 3 illustrate the structure for contacting the heat sink 50 to the conductor pattern 32 by means of the brazing metal 21, the heat sink 50 may be contacted to the conductor pattern 32 by, for example, solid phase diffusion bonding or die casting bonding for contacting a ceramic with a metal using a functionally graded material that changes its composition and structure depending on position without using a brazing metal. Alternatively, the brazing metal 21 may be directly contacted to the insulating substrate 31 without using the conductor pattern 32.Although the rear surface of the heat sink 50 is flat, the heat sink 50 may have fins such as pin fins or straight fins.< 1>Although the holders 61 and 611 are integrally formed with the resin case 60 using the same resin, the holders 61 and 611 described in the above-described semiconductor device module 100 may be formed separately from the resin case 60.FIG. 4 is a cross-sectional view (corresponding to the cross-section taken along the line B-B in the direction of the arrows of FIG. 1 ) in the case where a holder 62 formed separately from the resin case 60 is used.The holder 62 is disposed between the wall of the resin case 60 and the portion 601 to support the tip of the lead electrode 40. The holder 62 can be fixed by, for example, fitting both ends thereof into recesses or slits formed in the wall of the resin case 60 and the portion 601.The holder 62 may be made of a material identical to or different from that of the resin case 60. The holder 62, which is made of a material having higher heat resistance, for example, a metal or a resin having a heat resistance temperature higher than that of the resin case 60, does not melt even if a brazing metal having a high melting point is used as the brazing metal 22 for contacting the semiconductor devices with the lead electrodes 40 and 41. Thereby, an advantage of supporting the lead electrodes can be maintained.As a result, forming the holder 62 separately from the resin case 60 can not only expand options for materials, but can simplify the structure of the resin case 60 and reduce manufacturing cost.The holder 62 may be fixed to the resin case 60 by, for example, crimping or fastening screws.< 2>Although the structure including the through holes HL in the regions of the holders 61 and 611 for supporting the respective lead electrodes 40 and 41 is described in the semiconductor device module 100 as above, the holders may have a plurality of recesses DP on the surface, such as a holder 63 illustrated in FIG. 5.FIG. 5 is a cross-sectional view (corresponding to the cross-sectional view taken along the line B-B in FIG. 1 in the direction of the arrows) when the holder 63 integrally formed with the resin case 60 is used.Applying this structure can increase a surface area of the holder 63 and improve adhesion to the sealing material 70, and more reduce thermal displacement of the lead electrodes 40 and 41 due to heat generated when an electric current is applied to the semiconductor devices. Thereby, the stress applied to the semiconductor devices and the brazing metals can be alleviated, and the reliability of the semiconductor device module can be further improved.< 3>Although the structure including the through holes HL in the regions of the holders 61 and 611 for supporting the respective lead electrodes 40 and 41 is described in the semiconductor device module 100 as described above, the holder may have a corrugated surface with repeated protrusions and recesses, such as a holder 64 illustrated in FIG. 6.FIG. 6 is a cross-sectional view (corresponding to the cross-sectional view taken along the line B-B in FIG. 1 in the direction of the arrows) when the holder 64 integrally formed with the resin case 60 is used.Applying this structure can increase a surface area of the holder 64 and improve adhesion to the sealing material 70, and more reduce thermal displacement of the lead electrodes 40 and 41 due to heat generated when an electric current is applied to the semiconductor devices. Thereby, the stress applied to the semiconductor devices and the brazing metals can be alleviated, and the reliability of the semiconductor device module can be further improved.<Modifikation 4>Obwohl the configuration including the through holes HL in the regions of the holders 61 and 611 for supporting the respective lead electrodes 40 and 41 in the semiconductor device module 100 as described above, the entire holders may have a plurality of slits SL, like the holders 65 and 651 illustrated in FIG. 7.The plurality of slits SL are provided at intervals along long sides of the holders 65 and 651, which represent narrow rectangles in a plan view. The slits have about half the length of the short sides of the holders 65 and 651. The slits SL provided along the long sides of the holders 65 and 651 are arranged in a staggered manner in each of the holders so as not to be connected to each other. As long as the slits SL prevent the holders 65 and 651 from breaking, they are not limited to those whose arrangement and lengths have been described. Alternatively, the slits may be replaced with notches.Applying this structure can increase a surface area of the holders 65 and 651 and improve adhesion to the sealing material 70, and more reduce thermal displacement of the lead electrodes 40 and 41 due to heat generated when an electric current is applied to the semiconductor devices. Thereby, the stress applied to the semiconductor devices and the brazing metals can be further mitigated, and the reliability of the semiconductor device module can be further improved.Since the visibility immediately below the holders is improved by the plurality of slits SL provided, positioning of the lead electrodes and the semiconductor devices is facilitated when the resin package 60 is placed on the heat sink 50. Thereby, improvement in productivity can be expected.The slits can be processed more easily than the corrugated holder 64 illustrated in FIG. 6, thereby suppressing an increase in manufacturing cost.< 5>Although the structure including the through holes HL in the regions of the holders 61 and 611 for supporting the respective lead electrodes 40 and 41 is described in the semiconductor device module 100 as above, the entire holders may have a plurality of openings OP, such as the holders 66 and 661 illustrated in FIG. 8. The plurality of openings OP are provided at intervals in the center of the holders 65 and 651 along a longitudinal direction. Although the openings OP are circular in a plan view in FIG. 8, they may be rectangular, oval, or elliptical.Applying this structure can increase a surface area of the holders 66 and 661 and improve adhesion to the sealing material 70, and more reduce thermal displacement of the lead electrodes 40 and 41 due to heat generated when an electric current is applied to the semiconductor devices. Thereby, the stress applied to the semiconductor devices and the brazing metals can be alleviated, and the reliability of the semiconductor device module can be further improved.Since the visibility immediately below the holders is improved by the plurality of provided openings OP, positioning of the lead electrodes and the semiconductor devices is facilitated when the resin package 60 is placed on the heat sink 50. Thereby, improvement in productivity can be expected.The apertures can be more easily processed than the corrugated holder 64 illustrated in Figure 6. Thereby, an increase in manufacturing cost can be suppressed.Although the holders are integrally formed with the resin case 60 in the above-described modifications 2 to 5, they may be formed separately from the resin case 60 and to the resin case 60 by, for example, fitting (tight. These may be fixed by crimping, or fastening screws. In such a case, the structure of the resin case 60 can be simplified, and the manufacturing cost can be reduced.When the holders are integrally formed with the resin case 60, the number of components can be reduced, and operations for fixing the holders are eliminated. This can simplify the manufacturing processes.<Ausführungsform 2>FIG. 9 is a plan view illustrating a configuration of a semiconductor device module 200 according to Embodiment 2 of the present invention. Although the semiconductor device module illustrated in FIG. 9 is the one that packages power devices such as an IGBT, a MOSFET, and an FWD as a module, similarly to the semiconductor device module illustrated in FIG. 1, FIG. 9 illustrates a single-phase inverter. In FIG. 9, the same reference numerals are attached for the same configuration as in the semiconductor device module 100 described with reference to FIG. 1, and overlapping description is omitted.Nowadays, when the high-performance semiconductor device modules are desired, a number of semiconductor devices connected in parallel tends to increase, thereby enlarging the modules even when single-phase inverters are incorporated.In FIG. 9, the circuit patterns 302 and 303 are disposed on the insulating substrate 31. The switching devices T 1 and the diode devices D 1 are mounted on the circuit pattern 302, and the switching devices T 11 and the diode devices D 11 are mounted on the circuit pattern 303. The switching devices T 1 and the diode devices D 1 are each four parallel-connected devices, and the switching devices T 11 and the diode devices D 11 are also each four parallel-connected devices.An increase in the number of semiconductor devices connected in parallel increases the areas of the circuit patterns 302 and 303, and increases aspect ratios of one of the ends of the line electrodes 40 and 41.One end of the line electrode 41 is formed longer in a longitudinal direction (Y direction) to cover the top of the four switching devices T 11 arranged in the longitudinal direction and the four diode devices D 11 arranged in parallel with the four switching devices T 11, thereby having a greater aspect ratio of the length in the longitudinal direction and the length in the transverse direction. A protruding portion extending in the transverse direction from the central portion of the one end of the lead electrode 41, which is formed longer in the longitudinal direction, is contacted with the circuit pattern 302 via the brazing metal 23.As the aspect ratios of the one ends of the lead electrodes 40 and 41 increase, fixing the tips thereof solely by the holders may cause deformation due to the thermal displacement. Therefore, the lead electrode 40 whose one end is longer in the longitudinal direction includes the one end tip support bracket 61 and the two longitudinal end portion support brackets 613.The two holders 613 are disposed between the holder 61 and the wall of the resin case 60 to be perpendicular to the holder 61.By adopting such a structure, deformation due to thermal displacement at both end portions of one end of the lead electrode 40 in the lateral direction can be reduced.Moreover, the lead electrode 41 whose one end is longer in the longitudinal direction includes the one end tip support bracket 611 and the two longitudinal end center portion support brackets 612.The holder 612 is disposed between the wall of the resin case 60 and the portion 601 to be parallel to the holder 611.By adopting such a structure, the deformation due to the thermal displacement in the central portion of the one end of the lead electrode 41 in the longitudinal direction can be reduced.The holder 613 and the holder 612 may be referred to as auxiliary holders because they respectively support the functions of the holder 61 and the holder 611.Obviously, the holders 612 and 613 may have the same configuration as those in Modifications 1 to 5 of Embodiment 1.<Example Configuration of Power Device>The above-mentioned power devices such as an IGBT, a MOSFET, and an FWD included in the power semiconductor modules according to Embodiments 1 and 2 are not limited to silicon devices including silicon (Si) semiconductors, but may be semiconductor devices having a band gap larger than those of the silicon devices, such as silicon carbide (SiC), gallium nitride (GaN), and diamond (C). As compared with the silicon devices, the application of these semiconductor devices can result in devices superior in withstand voltage, higher allowable current density, higher heat resistance, and high temperature operation.Thus, the power devices are subjected to a higher temperature, and the thermal displacement easily occurs in the line electrodes. However, the thermal shift can be reduced by employing the present invention.

Claims

A semiconductor device module comprising: • a semiconductor device (T1, T11, D1, D11) comprising an upper electrode and a lower electrode; • a substrate (31) on which the lower electrode of the semiconductor device is contacted; • a heat sink (50) on which the substrate is mounted; • a lead electrode (40, 41, 42) through which a main current of the semiconductor device flows; • an insulating case (60) arranged to enclose the substrate; • a holder (61 to 65, 611) disposed in a beam-like shape in the insulating case, the holder supporting the lead electrode, • one end of the lead electrode being brazed to the upper electrode of the semiconductor device (T1, T11, D1, D11), and another end side being inserted into a wall of the insulating case, • the holder engaging the one end of the lead electrode to restrict movement of the lead electrode, and • a portion of the holder supporting the lead electrode having a through hole penetrating the holder in the thickness direction.The semiconductor device module according to claim 1, wherein • the insulating case is filled with a sealing material (70), and • the holder comprises a plurality of recesses (DP) on a surface of the holder.The semiconductor device module according to claim 1, wherein • the insulating case is filled with a sealing material (70), and • the holder has a corrugated surface with repeated protrusions and recesses.The semiconductor device module according to claim 1, wherein • the insulating case is filled with a sealing material (70), and • the holder comprises a plurality of slits (SL) on a surface of the holder.A semiconductor device module comprising: • a semiconductor device (T1, T11, D1, D11) comprising an upper electrode and a lower electrode; • a substrate (31) on which the lower electrode of the semiconductor device is contacted; • a heat sink (50) on which the substrate is mounted; • a lead electrode (40, 41, 42) through which a main current of the semiconductor device flows; • an insulating case (60) arranged to enclose the substrate; • a holder (61 to 65, 611) disposed in a beam-like shape in the insulating case, the holder supporting the lead electrode, • one end of the lead electrode being brazed to the upper electrode of the semiconductor device (T1, T11, D1, D11), and another end side being inserted into a wall of the insulating case, • the holder engaging the one end of the lead electrode to restrict movement of the lead electrode, • the insulating case being filled with a sealing material (70), and • the holder comprising a plurality of openings (OP) penetrating the holder in a thickness direction.The semiconductor device module according to claim 1, wherein the holder engages with an upper surface and a side surface of the one end of the lead electrode.The semiconductor device module according to any one of claims 1 to 6, wherein the holder is integrally formed with the insulating case.The semiconductor device module according to any one of claims 1 to 6, wherein the holder is formed separately from the insulating case.The semiconductor device module according to claim 8, wherein the holder is made of a material different from the material of the insulating caseThe semiconductor device according to claim 1, further comprising • an additional holder (612, 613) provided in a cantilever manner in the insulating case, wherein the additional holder supports a function of the holder, • the additional holder is disposed parallel or perpendicular to the holder, and • the additional holder engages a portion of the one end of the lead electrode, which is a portion that the holder does not engage.

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