Semiconductor power module having an improved composite board and method of fabricating the same

• US 5,521,437 A
• Filed: 07/05/1994
• Issued: 05/28/1996
• Est. Priority Date: 07/05/1993
• Status: Expired due to Fees

• Current Assignee: BC Acquisition Corp. (BioClinica, Inc.)
• Original Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Inventors: Oota, Tatsuo, Oshima, Seiichi
• Primary Examiner(s): Limanek, Robert P.
• Assistant Examiner(s): Hardy, David B.
• Application Number:
  US08/270,372
• Time in Patent Office: 693 Days
• Field of Search: 257/607, 257/701, 257/702, 257/706, 257/707, 257/723, 257/724, 257/500
• US Class Current: 257/701
• CPC Class Codes: H01L 2224/05599 Material
• CPC Class Codes: H01L 2224/2612 Auxiliary members for layer connectors, e.g. spacers
• CPC Class Codes: H01L 2224/32225 the item being non-metallic, e.g. insulating substrate with or without metallisation
• CPC Class Codes: H01L 2224/45124 Aluminium (Al) as principal constituent
• CPC Class Codes: H01L 2224/48091 Arched
• CPC Class Codes: H01L 2224/48137 the bodies being arranged next to each other, e.g. on a common substrate
• CPC Class Codes: H01L 2224/48227 connecting the wire to a bond pad of the item
• CPC Class Codes: H01L 2224/48472 the other connecting portion not on the bonding area also being a wedge bond, i.e. wedge-to-wedge
• CPC Class Codes: H01L 2224/73265 Layer and wire connectors
• CPC Class Codes: H01L 2224/92247 the second connecting process involving a wire connector
• CPC Class Codes: H01L 23/24 solid or gel at the normal operating temperature of the device H01L23/3135 takes precedence
• CPC Class Codes: H01L 23/5385 Assembly of a plurality of insulating substrates
• CPC Class Codes: H01L 24/32 of an individual layer connector
• CPC Class Codes: H01L 24/45 of an individual wire connector
• CPC Class Codes: H01L 24/48 of an individual wire connector
• CPC Class Codes: H01L 25/16 the devices being of types provided for in two or more different main groups of groups H01L27/00 - H01L33/00, or in a single subclass of H10K, H10N, e.g. forming hybrid circuits
• CPC Class Codes: H01L 2924/00 Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
• CPC Class Codes: H01L 2924/00012 Relevant to the scope of the group, the symbol of which is combined with the symbol of this group
• CPC Class Codes: H01L 2924/00014 the subject-matter covered by the group, the symbol of which is combined with the symbol of this group, being disclosed without further technical details
• CPC Class Codes: H01L 2924/01005 Boron [B]
• CPC Class Codes: H01L 2924/01006 : Carbon [C]
• CPC Class Codes: H01L 2924/01013 : Aluminum [Al]
• CPC Class Codes: H01L 2924/01023 : Vanadium [V]
• CPC Class Codes: H01L 2924/01029 : Copper [Cu]
• CPC Class Codes: H01L 2924/01033 : Arsenic [As]
• CPC Class Codes: H01L 2924/01074 : Tungsten [W]
• CPC Class Codes: H01L 2924/1305 : Bipolar Junction Transistor [BJT]
• CPC Class Codes: H01L 2924/13055 : Insulated gate bipolar transistor [IGBT]
• CPC Class Codes: H01L 2924/181 : Encapsulation
• CPC Class Codes: H05K 1/05 : Insulated conductive substrates, e.g. insulated metal substrate
• CPC Class Codes: H05K 1/142 : Arrangements of planar printed circuit boards in the same plane, e.g. auxiliary printed circuit insert mounted in a main printed circuit

Abstract

An insulating metallic board 160 mounting IGBTs which control an electrical power and other circuit elements and an insulating board 170 mounting semiconductor elements which control the IGBTs and the other circuit elements are arranged adjacent to or closely parallel to each other, and combined by a frame 180 into one integral circuit board to define a composite board 150. Wiring patterns 161 and 171 on which the respective circuit elements are to be disposed are formed on major surfaces of the same side. Since the composite board 150 which includes the two different types of circuit boards can be treated simply as one board, it is possible to mount the circuit elements onto the two different types of boards at the same time in one fabrication step. Thus, the number of fabrication steps and a manufacturing cost are reduced.

Claims

1. A semiconductor power module comprising:

(a) a composite board which includes an insulating metallic board which includes a metallic plate, a main circuit wiring pattern being disposed on an insulating layer which is formed on a major surface of said insulating metallic board, said insulating layer comprising an epoxy resin; and

an insulating board which includes an insulating member, a control circuit wiring pattern being disposed on a major surface of said insulating board, said insulating board being disposed adjacent to said insulating metallic board in such a manner that said major surface of said insulating board on which said control circuit wiring pattern is formed is flush with said major surface of said insulating metallic board on which said main circuit wiring pattern is formed,

a major surface of said metallic plate being exposed in a bottom surface of said composite board which is opposite said major surfaces of said insulating metallic board and said insulating board seating said main and said control circuit wiring patterns, respectively;

(b) a power control semiconductor element disposed on said main circuit wiring pattern to control electrical power, said power control semiconductor element including a plurality of insulated gate bipolar transistors;

(c) a control element disposed on said control circuit wiring pattern to control said power control semiconductor element, said control element outputting control signals to respective gate electrodes of said insulated gate bipolar transistors;

(d) a cylindrical case for receiving at an end thereof a peripheral portion of said composite board so as to contain said power control semiconductor element and said control element inside; and

(e) a sealing resin injected into said case to seal said power control semiconductor element and said control element.

2. The semiconductor power module of claim 1, further including a high potential power supply terminal, a low potential power supply terminal and at least one output terminal, wherein

said plurality of insulated gate bipolar transistors include first and second insulated gate bipolar transistors, said first insulated gate bipolar transistors being disposed between said high potential power supply terminal and said at least one output terminal, and said second insulated gate bipolar transistors being disposed between said at least one output terminal and said low potential power supply terminal.

3. The semiconductor power module of claim 2, wherein said at least one output terminal includes a plurality of output terminals,

said first insulated gate bipolar transistors are each disposed between said high potential power supply terminal and each one of said plurality of output terminals, and

said second insulated gate bipolar transistors are each disposed between each one of said plurality of output terminals and said low potential power supply terminal.

4. The semiconductor power module of claim 1, wherein said metallic plate comprises aluminum.

5. The semiconductor power module of claim 1, wherein said power control semiconductor element further includes fly wheel diodes which are respectively connected to said insulated gate bipolar transistors.

6. The semiconductor power module of claim 5, wherein said fly wheel diodes are connected to said main circuit wiring pattern through an electrically conductive heat sink member.

7. The semiconductor power module of claim 1, wherein one of said insulating metallic board and said insulating board of said composite board includes an opening to receive the other for engagement.

8. The semiconductor power module of claim 7, wherein said insulating board of said composite board includes said opening which extends from said major surface to an opposite major surface of said insulating board, and said insulating metallic board is fit in said opening of said insulating board.

9. The semiconductor power module of claim 1, wherein no part thereof extends beyond said major surface of said metallic plate which is exposed in said bottom surface of said composite board.

10. The semiconductor power module of claim 9, wherein said major surface of said metallic plate which is exposed in said bottom surface of said composite board and said second major surface of said frame member are flush with one another.

11. The semiconductor power module of claim 9, wherein said major surface of said metallic plate which is exposed in said bottom surface of said composite board extends beyond said second major surface of said frame member.

12. The semiconductor power module of claim 9, wherein said major surface seating said main circuit wiring pattern and said major surface seating said control circuit wiring pattern are adjusted to be flush with each other in said composite board.

13. The semiconductor power module of claim 1, wherein said insulating metallic board, said insulating board, and said cylindrical case are fixed to each other by said sealing resin.

14. A semiconductor power module comprising:

(a) a composite board which includes

an insulating metallic board which includes a metallic plate, a main circuit wiring pattern being disposed on an insulating layer which is formed on a major surface of said insulating metallic board; and

an insulating board which includes an insulating member, a control circuit wiring pattern being disposed on a major surface of said insulating board, said insulating board being disposed adjacent to said insulating metallic board in such a manner that said major surface of said insulating board on which said control circuit wiring pattern is formed is flush with said major surface of said insulating metallic board on which said main circuit wiring pattern is formed, said insulating member comprising a fiber reinforced epoxy resin,

a major surface of said metallic plate being exposed in a bottom surface of said composite board which is opposite said major surfaces of said insulating metallic board and said insulating board seating said main and said control circuit wiring patterns, respectively;

(b) a power control semiconductor element disposed on said main circuit wiring pattern to control electrical power, said power control semiconductor element including a plurality of insulated gate bipolar transistors;

(c) a control element disposed on said control circuit wiring pattern to control said power control semiconductor element, said control element outputting control signals to respective gate electrodes of said insulated gate bipolar transistors;

(d) a cylindrical case for receiving at an end thereof a peripheral portion of said composite board so as to contain said power control semiconductor element and said control element inside; and

(e) a sealing resin injected into said case to seal said power control semiconductor element and said control element.

15. The semiconductor power module of claim 14, further including a high potential power supply terminal, a low potential power supply terminal and at least one output terminal, wherein

said plurality of insulated gate bipolar transistors include first and second insulated gate bipolar transistors, said first insulated gate bipolar transistors being disposed between said high potential power supply terminal and said at least one output terminal, and said second insulated gate bipolar transistors being disposed between said at least one output terminal and said low potential power supply terminal.

16. The semiconductor power module of claim 15, wherein said at least one output terminal includes a plurality of output terminals,

said first insulated gate bipolar transistors are each disposed between said high potential power supply terminal and each one of said plurality of output terminals, and

said second insulated gate bipolar transistors are each disposed between each one of said plurality of output terminals and said low potential power supply terminal.

17. The semiconductor power module of claim 14, wherein said metallic plate comprises aluminum.

18. The semiconductor power module of claim 14, wherein said power control semiconductor element further includes fly wheel diodes which are respectively connected to said insulated gate bipolar transistors.

19. The semiconductor power module of claim 18, wherein said fly wheel diodes are connected to said main circuit wiring pattern through an electrically conductive heat sink member.

20. The semiconductor power module of claim 14, wherein one of said insulating metallic board and said insulating board of said composite board includes an opening to receive the other for engagement.

21. The semiconductor power module of claim 20, wherein said insulating board of said composite board includes said opening which extends from said major surface to an opposite major surface of said insulating board, and said insulating metallic board is fit in said opening of said insulating board.

22. The semiconductor power module of claim 14, wherein no part thereof extends beyond said major surface of said metallic plate which is exposed in said bottom surface of said composite board.

23. The semiconductor power module of claim 22, wherein said major surface of said metallic plate which is exposed in said bottom surface of said composite board and said second major surface of said frame member are flush with one another.

24. The semiconductor power module of claim 22, wherein said major surface of said metallic plate which is exposed in said bottom surface of said composite board extends beyond said second major surface of said frame member.

25. The semiconductor power module of claim 22, wherein said major surface seating said main circuit wiring pattern and said major surface seating said control circuit wiring pattern are adjusted to be flush with each other in said composite board.

26. The semiconductor power module of claim 14, wherein said insulating metallic board, said insulating board, and said cylindrical case are fixed to each other by said sealing resin.

27. A semiconductor power module comprising:

(a) a composite board which includes an insulating metallic board which includes a metallic plate, a main circuit wiring pattern being disposed on an insulating layer which is formed on a major surface of said insulating metallic board; and

an insulating board which includes an insulating member, a control circuit wiring pattern being disposed on a major surface of said insulating board, said insulating board being disposed adjacent to said insulating metallic board in such a manner that said major surface of said insulating board on which said control circuit wiring pattern is formed is flush with said major surface of said insulating metallic board on which said main circuit wiring pattern is formed,

a major surface of said metallic plate being exposed in a bottom surface of said composite board which is opposite said major surfaces of said insulating metallic board and said insulating board seating said main and said control circuit wiring patterns, respectively;

(b) a power control semiconductor element disposed on said main circuit wiring pattern to control electrical power, said power control semiconductor element including a plurality of insulated gate bipolar transistors;

(c) a control element disposed on said control circuit wiring pattern to control said power control semiconductor element, said control element outputting control signals to respective gate electrodes of said insulated gate bipolar transistors;

(d) a cylindrical case for receiving at an end thereof a peripheral portion of said composite board so as to contain said power control semiconductor element and said control element inside;

(e) a sealing resin injected into said case to seal said power control semiconductor element and said control element; and

(f) an electrically conductive heat sink member disposed between said first and second insulated gate bipolar transistors and said main circuit wiring pattern.

28. The semiconductor power module of claim 27, further including a high potential power supply terminal, a low potential power supply terminal and at least one output terminal, wherein

said plurality of insulated gate bipolar transistors include first and second insulated gate bipolar transistors, said first insulated gate bipolar transistors being disposed between said high potential power supply terminal and said at least one output terminal, and said second insulated gate bipolar transistors being disposed between said at least one output terminal and said low potential power supply terminal.

29. The semiconductor power module of claim 28, wherein said at least one output terminal includes a plurality of output terminals,

said first insulated gate bipolar transistors are each disposed between said high potential power supply terminal and each one of said plurality of output terminals, and

said second insulated gate bipolar transistors are each disposed between each one of said plurality of output terminals and said low potential power supply terminal.

30. The semiconductor power module of claim 27, wherein said metallic plate comprises aluminum.

31. The semiconductor power module of claim 27, wherein said power control semiconductor element further includes fly wheel diodes which are respectively connected to said insulated gate bipolar transistors.

32. The semiconductor power module of claim 31, wherein said fly wheel diodes are connected to said main circuit wiring pattern through an electrically conductive heat sink member.

33. The semiconductor power module of claim 27, wherein one of said insulating metallic board and said insulating board of said composite board includes an opening to receive the other for engagement.

34. The semiconductor power module of claim 33, wherein said insulating board of said composite board includes said opening which extends from said major surface to an opposite major surface of said insulating board, and said insulating metallic board is fit in said opening of said insulating board.

35. The semiconductor power module of claim 27, wherein no part thereof extends beyond said major surface of said metallic plate which is exposed in said bottom surface of said composite board.

36. The semiconductor power module of claim 35, wherein said major surface of said metallic plate which is exposed in said bottom surface of said composite board and said second major surface of said frame member are flush with one another.

37. The semiconductor power module of claim 35, wherein said major surface of said metallic plate which is exposed in said bottom surface of said composite board extends beyond said second major surface of said frame member.

38. The semiconductor power module of claim 35, wherein said major surface seating said main circuit wiring pattern and said major surface seating said control circuit wiring pattern are adjusted to be flush with each other in said composite board.

39. The semiconductor power module of claim 27, wherein said insulating metallic board, said insulating board, and said cylindrical case are fixed to each other by said sealing resin.

40. A semiconductor power module comprising:

(a) a composite board which includes an insulating metallic board which includes a metallic plate, a main circuit wiring pattern being disposed on an insulating layer which is formed on a major surface of said insulating metallic board;

an insulating board which includes an insulating member, a control circuit wiring pattern being disposed on a major surface of said insulating board, said insulating board being disposed adjacent to said insulating metallic board in such a manner that said major surface of said insulating board on which said control circuit wiring pattern is formed is flush with said major surface of said insulating metallic board on which said main circuit wiring pattern is formed,

a major surface of said metallic plate being exposed in a bottom surface of said composite board which is opposite said major surfaces of said insulating metallic board and said insulating board seating said main and said control circuit wiring patterns, respectively; and

a frame member for combining said insulating metallic board and said insulating board into one integral board;

(b) a power control semiconductor element disposed on said main circuit wiring pattern to control electrical power;

(c) a control element disposed on said control circuit wiring pattern to control said power control semiconductor element;

(d) a cylindrical case for receiving at an end thereof a peripheral portion of said composite board so as to contain said power control semiconductor element and said control element inside; and

(e) a sealing resin injected into said case to seal said power control semiconductor element and said control element.

41. The semiconductor power module of claim 40, wherein said frame member has first and second major surfaces, and first and second openings, said first opening penetrating said frame member from said first major surface to said second major surface of said frame member, said second opening being open on said first major surface but closed on said second major surface of said frame member, said insulating metallic board being fit into said first opening in such a manner that said main circuit wiring pattern is on a first major surface side, and said insulating board being fit into said second opening in such a manner that said control circuit wiring pattern is on said first major surface side.

42. The semiconductor power module according to claim 41, wherein said frame member has an extending protrusion which has a through hole.

43. The semiconductor power module according to claim 41, wherein a ridge is formed along a periphery of said cylindrical case and said end thereof, and a groove is formed along a periphery of said frame member for engagement with said ridge.

44. The semiconductor power module of claim 41, wherein said insulating metallic board and said insulating board are both fixed to said frame member by an adhesive agent.

45. The semiconductor power module of claim 44, wherein said adhesive agent comprises a heat-resistant resin.

46. The semiconductor power module of claim 45, wherein said resin is polyphenylene sulfide.

47. The semiconductor power module of claim 41, wherein said first opening includes an extending protrusion at an end of said first opening so as to prevent said insulating metallic board which is inserted into said first opening from sliding toward said first major surface side from its inserted position.

48. A semiconductor power module comprising:

(a) a composite board which includes an insulating metallic board which includes a metallic plate, a main circuit wiring pattern being disposed on an insulating layer which is formed on a major surface of said insulating metallic board; and

an insulating board which includes an insulating member, a control circuit wiring pattern being disposed on a major surface of said insulating board, and an extending protrusion which has a through hole, said insulating board being disposed adjacent to said insulating metallic board in such a manner that said major surface of said insulating board on which said control circuit wiring pattern is formed is flush with said major surface of said insulating metallic board on which said main circuit wiring pattern is formed,

a major surface of said metallic plate being exposed in a bottom surface of said composite board which is opposite said major surfaces of said insulating metallic board and said insulating board seating said main and said control circuit wiring patterns, respectively,

said insulating board of said composite board including an opening to receive said insulating metallic board for engagement, said opening extending from said major surface to an opposite major surface of said insulating board;

(b) a power control semiconductor element disposed on said main circuit wiring pattern to control electrical power;

(c) a control element disposed on said control circuit wiring pattern to control said power control semiconductor element;

(d) a cylindrical case for receiving at an end thereof a peripheral portion of said composite board so as to contain said power control semiconductor element and said control element inside; and

(e) a sealing resin injected into said case to seal said power control semiconductor element and said control element.

49. A semiconductor power module comprising:

(a) a composite board which includes an insulating metallic board which includes a metallic plate, a main circuit wiring pattern being disposed on an insulating layer which is formed on a major surface of said insulating metallic board;

an insulating board which includes an insulating member, a control circuit wiring pattern being disposed on a major surface of said insulating board, said insulating board being disposed adjacent to said insulating metallic board in such a manner that said major surface of said insulating board on which said control circuit wiring pattern is formed is flush with said major surface of said insulating metallic board on which said main circuit wiring pattern is formed,

a major surface of said metallic plate being exposed in a bottom surface of said composite board which is opposite said major surfaces of said insulating metallic board and said insulating board seating said main and said control circuit wiring patterns, respectively,

said insulating board of said composite board including an opening to receive said insulating metallic board for engagement, said opening extending from said major surface to an opposite major surface of said insulating board; and

a frame member for combining said insulating metallic board and said insulating board into one integral board, a groove being formed along a periphery of said frame member;

(b) a power control semiconductor element disposed on said main circuit wiring pattern to control electrical power;

(c) a control element disposed on said control circuit wiring pattern to control said power control semiconductor element;

(d) a cylindrical case for receiving at an end thereof a peripheral portion of said composite board so as to contain said power control semiconductor element and said control element inside, a ridge being formed along a periphery of said cylindrical case at said end thereof for engagement with said groove of said frame member; and

(e) a sealing resin injected into said case to seal said power control semiconductor element and said control element.

50. A semiconductor power module comprising:

(a) a composite board which includes an insulating metallic board which includes a metallic plate, a main circuit wiring pattern being disposed on an insulating layer which is formed on a major surface of said insulating metallic board; and

an insulating board which includes an insulating member, a control circuit wiring pattern being disposed on a major surface of said insulating board, said insulating board being disposed adjacent to said insulating metallic board in such a manner that said major surface of said insulating board on which said control circuit wiring pattern is formed is flush with said major surface of said insulating metallic board on which said main circuit wiring pattern is formed,

a major surface of said metallic plate being exposed in a bottom surface of said composite board which is opposite said major surfaces of said insulating metallic board and said insulating board seating said main and said control circuit wiring patterns, respectively,

said insulating board of said composite board including an opening to receive said insulating metallic board for engagement, said opening extending from said major surface to an opposite major surface of said insulating board, said opening including an extending protrusion at an end thereof so as to prevent said insulating metallic board from sliding toward said main circuit wiring pattern from its inserted position;

(b) a power control semiconductor element disposed on said main circuit wiring pattern to control electrical power;

(c) a control element disposed on said control circuit wiring pattern to control said power control semiconductor element;

(d) a cylindrical case for receiving at an end thereof a peripheral portion of said composite board so as to contain said power control semiconductor element and said control element inside; and

(e) a sealing resin injected into said case to seal said power control semiconductor element and said control element.

51. A semiconductor power module comprising:

(a) a composite board which includes an insulating metallic board which includes a metallic plate, a main circuit wiring pattern being disposed on an insulating layer which is formed on a major surface of said insulating metallic board; and

an insulating board which includes an insulating member, a control circuit wiring pattern being disposed on a major surface of said insulating board, said insulating board being disposed adjacent to said insulating metallic board in such a manner that said major surface of said insulating board on which said control circuit wiring pattern is formed is flush with said major surface of said insulating metallic board on which said main circuit wiring pattern is formed,

a major surface of said metallic plate being exposed in a bottom surface of said composite board which is opposite said major surfaces of said insulating metallic board and said insulating board seating said main and said control circuit wiring patterns, respectively,

said insulating metallic board and said insulating board of said composite board being disposed adjacent to each other and bonded to each other by an adhesive agent;

(b) a power control semiconductor element disposed on said main circuit wiring pattern to control electrical power;

(c) a control element disposed on said control circuit wiring pattern to control said power control semiconductor element;

(d) a cylindrical case for receiving at an end thereof a peripheral portion of said composite board so as to contain said power control semiconductor element and said control element inside; and

(e) a sealing resin injected into said case to seal said power control semiconductor element and said control element.

52. A method of fabricating a semiconductor power module, comprising the steps of:

(a) preparing a composite board which comprises;

(i) an insulating metallic board which includes a metallic plate, a main circuit wiring pattern being disposed on an insulating layer which is formed on a major surface of said insulating metallic board through an insulating layer; and

(ii) an insulating board which includes an insulating member, a sub circuit wiring pattern being disposed on a major surface of said insulating board, said insulating board being disposed adjacent to said insulating metallic board in such a manner that said major surface of said insulating board on which said sub circuit wiring pattern is formed is flush with said major surface of said insulating metallic board on which said main circuit wiring pattern is formed;

a major surface of said metallic plate being exposed in a bottom surface of said composite board which is opposite said major surfaces of said insulating metallic board and said insulating board seating said main and said control circuit wiring patterns, respectively;

(b) preparing a cylindrical case;

(c) mounting a power control semiconductor element which controls electrical power and mounting a main terminal on said main circuit wiring pattern, said step (c) including the steps of;

(c-1) applying a first solder on said main circuit wiring pattern;

(c-2) placing said power control semiconductor element and said main terminal on said first solder;

(c-3) heating said first solder after said step (c-2);

(c-4) cooling said first solder down to room temperature after said step (c-3);

(c-5) applying a third solder on said main circuit wiring pattern;

(c-6) placing an electrically conductive heat sink member on said third solder;

(c-7) applying a fourth solder on said heat sink member;

(c-8) placing said power control semiconductor element and said main terminal on said fourth solder;

(c-9) heating said third and said fourth solders after said step (c-8); and

(c-10) cooling said third and said fourth solders down to room temperature after said step (c-9);

(d) mounting a control element and a sub terminal on said sub circuit wiring pattern;

(e) engaging an end portion of said cylindrical case with a peripheral portion of said composite board which mounts said power control semiconductor element and said control element so that said cylindrical case contains said power control semiconductor element and said control element therein; and

(f) filling said cylindrical case with a sealing resin for sealing said power control semiconductor element and said control element in such a manner that an end of each of said main terminal and said sub terminal is exposed outside said sealing resin.

53. The method of claim 52, wherein said step (d) comprises the steps of:

(d-1) applying a second solder on said sub circuit wiring pattern;

(d-2) placing said control element and said sub terminal on said second solder;

(d-3) heating said second solder after said step (d-2) but concurrently with said step (c-3); and

(d-4) cooling said second solder down to room temperature after said step (d-3) but concurrently with said step (c-4).

54. The method of claim 52, wherein said step (d) comprises the steps of:

(d-1) applying a fifth solder on said sub circuit wiring pattern;

(d-2) placing said control element and said sub terminal on said fifth solder;

(d-3) heating said fifth solder after said step (d-2) but concurrently with said step (c-9); and

(d-4) cooling said fifth solder down to room temperature after said step (d-3) but concurrently with said step (c-10).

55. The method of claim 52, wherein said step (e) comprises the step of fixing said one end portion of said cylindrical case to said peripheral portion of said composite board by an adhesive agent.

56. The method of claim 52, wherein said step (f) comprises the steps of:

(f-1) filling said case with a thermosetting resin;

(f-2) heating said thermosetting resin; and

(f-3) cooling said thermosetting resin down to room temperature.