Semiconductor electrical heater and method for making same

• US 5,498,850 A
• Filed: 06/08/1993
• Issued: 03/12/1996
• Est. Priority Date: 09/11/1992
• Status: Expired due to Fees

• Current Assignee: Philip Morris Incorporated (Altria Group, Inc.)
• Original Assignee: Philip Morris Incorporated (Altria Group, Inc.)
• Inventors: Das, Amitabh
• Primary Examiner(s): Lateef, Marvin M.
• Assistant Examiner(s): Pelham, J.
• Application Number:
  US08/073,539
• Time in Patent Office: 1,008 Days
• Field of Search: 219/121.63, 219/121.64, 219/121.65, 219/121.66, 219/121.85
• US Class Current: 219/121.66
• CPC Class Codes: A24F 40/46 Shape or structure of electric heating means
• CPC Class Codes: A24F 40/70 Manufacture
• CPC Class Codes: B23K 2035/008 at least one of the workpieces being of silicium
• CPC Class Codes: B23K 2101/40 Semiconductor devices
• CPC Class Codes: B23K 26/22 Spot welding
• CPC Class Codes: B23K 35/007 at least one of the workpieces being of copper or another noble metal
• CPC Class Codes: B23K 35/302 Cu as the principal constituent
• 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 2924/0002 Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00

Abstract

A method is disclosed for mechanically and electrically bonding metallic materials and semiconductor materials. The method according to the invention may be used, for example, in forming a semiconductor electrical heater, particularly for use in electrical smoking articles. A metallic element, such as a copper alloy power supply tab, is laser welded to a semiconductor element, such as a doped silicon resistive heater element. A laser beam is directed through a hole in the copper alloy tab to melt some silicon material, which flows into the hole in the copper tab, reacts and intermixes with the copper and solidifies to form a slug containing copper silicide. A protective material such as nickel may be applied to protect the copper silicide from oxidation if desired. An ohmic, low resistance contact and high strength bond is provided between the parts.

Claims

1. A method of establishing an ohmic mechanical joint between a metallic element and a semiconductor element comprising the steps of:

superposing at least a portion of a metallic element with at least a portion of a semiconductor element;

directing a controlled amount of heat at said superposed portion of said semiconductor element through a hole in said superposed portion of said metallic element so as to cause an amount of semiconductor material to melt and flow into the hole and react with metallic material of said metallic element to form reacted materials, said melting, flowing and reacting steps including the step of at least partially filling said hole with said reacted materials; and

allowing the reacted materials to solidify in the hole to provide a joint having a substantially ohmic electrical resistance between the metallic element and the semiconductor element.

2. The method of claim 1, wherein the step of directing a controlled amount of heat comprises directing a laser beam at the semiconductor element through the hole in the metallic element.

3. The method of claim 2, wherein the step of directing a laser beam at the semiconductor element comprises pulsing a Nd:

YAG laser directed at the semiconductor element.

4. The method of claim 2, wherein a plurality of laser beam pulses are directed at the semiconductor element through the hole in the metallic element.

5. The method of claim 2, wherein the laser beam is directed substantially perpendicularly to a surface of the semiconductor element.

6. The method of claim 2, wherein the laser beam is directed at an angle other than substantially perpendicular to a surface of the semiconductor element.

7. The method of claim 2, wherein the laser beam is directed to at least partially impinge on the metallic material around the sides of the hole.

8. The method of claim 1, wherein the step of directing a controlled amount of heat comprises applying a microflame to the semiconductor element through the hole in the metallic element.

9. The method of claim 8, further comprising a step of providing an inert gas at the area of adjacent of the semiconductor element and the metallic element.

10. The method of claim 9 wherein the inert gas is selected from the group consisting of argon gas and nitrogen gas.

11. The method of claim 1 further comprising a step of forming the hole in the metallic element.

12. The method of claim 11, wherein the step of forming the hole comprises directing a laser beam at the metallic element.

13. The method of claim 12, wherein the step of forming the hole in the metallic element and step of directing a controlled amount of heat comprise applying a single laser beam.

14. The method of claim 1 further comprising a step of cleaning at least selected surface of one of the elements before said superposing step.

15. The method of claim 14, wherein the surface cleaning step comprises wet chemical etching.

16. The method of claim 14, wherein the surface cleaning step comprises mechanical cleaning.

17. The method of claim 1, wherein the superposing step includes holding the metallic element and the semiconductor element in intimate surface contact during at least said heat directing step and said step allowing reacted materials to solidify.

18. The method of claim 1, further comprising a step of preheating the semiconductor element and the metallic element before the step of directing a controlled amount of heat.

19. The method of claim 18, further comprising a step of providing an inert gas at the area of adjacent of the semiconductor element and the metallic element.

20. The method of claim 19 wherein the inert gas is selected from the group consisting of argon gas and nitrogen gas.

21. The method of claim 1 further comprising a step of applying an oxidation-resistant material over an exposed surface of the reacted materials.

22. The method of claim 21 wherein the step of applying an oxidation-resistant material comprises bonding the oxidation-resistant material to the exposed surface of the reacted materials.

23. The method of claim 21, wherein the step of applying an oxidation-resistant material comprises melting an oxidation-resistant metal.

24. The method of claim 23, wherein the step of melting an oxidation-resistant metal comprises melting nickel.

25. The method of claim 23, wherein the step of melting an oxidation-resistant metal comprises directing a laser beam at the oxidation-resistant metal.

26. The method of claim 1, wherein said metallic element is constructed from copper.

27. The method of claim 26, wherein said metallic element is constructed from an alloy of copper and a transition metal element that is resistant to oxidation and that forms compounds with the semiconductor material.

28. The method of claim 27, wherein said transition metal is selected from the group consisting of nickel, chromium, titanium and molybdenum.

29. The method of claim 1, wherein said metallic element is constructed from a copper-phosphor bronze alloy.

30. The method of claim 1, wherein said semiconductor element is constructed from silicon doped with dopant impurities to provide a predetermined electrical resistivity and wherein said metallic element is constructed from a metal that is reactive with the silicon to form a metal silicide compound.

31. The method of claim 2, wherein said semiconductor element is operatable as a resistive heater element and said metallic element is operable as an electrical lead to a power supply.

32. The method of claim 31, wherein said semiconductor element is constructed from silicon doped with dopant impurities and said metallic element is constructed from a copper alloy.

33. The method of claim 1 further comprising the step of:

applying a clip operative upon the metallic element and the semiconductor element so as to press said superposed portions together.

34. The method of claim 33, wherein said semiconductor element is operable as a resistive heater element and said metallic element is operable as an electrical lead to a power supply.

35. The method of claim 34, wherein said semiconductor element is constructed from silicon doped with dopant inpurities and said metallic element is constructed from a copper alloy.

36. The method of claim 1, wherein said semiconductor element has a thickness in the range from about 0.1 mm to about 0.5 mm.

37. The method of claim 1, wherein said metallic element comprises a foil having a thickness less than about 0.4 mm.

38. The method of claim 37, wherein said foil metallic element has a thickness less than about 0.25 mm.

39. The method of claim 38, wherein said foil metallic element has a thickness in the range from about 0.08 mm to about 0.2 mm.

40. The method of claim 39, wherein said foil metallic element has a thickness in the range from about 0.15 mm to about 0.2 mm.

41. The method of claim 1, wherein said metallic element hole has a diameter in the range from about 0.1 mm to about 0.8 mm.

42. The method of claim 1, wherein said heat directing step includes directing heat through a conic frustum-shaped hole therethrough.

43. The method of claim 1, wherein said heat directing step includes causing an amount of metallic material to melt.

44. The method of claim 43, wherein causing an amount of metallic material to melt comprises contacting the metallic material with molten semiconductor material.

45. The method of claim 43, wherein said step of causing an amount of metallic material to melt comprises directing a laser beam to at least partially impinge on the metallic material adjacent the hole.

46. The method of claim 1, wherein all steps are carried out in a total time of less than about 3 seconds.

47. The method of claim 46, wherein all steps are carried out in a total time of less than about 1 second.

48. The method of claim 47, wherein all steps are carried out in a total time of less than about 0.5 seconds.

49. The method of claim 1, wherein steps (c) and (d) are carried out in a total time between about 20 msec and about 50 msec.

50. The method of claim 1 further comprising the step of providing a metallic element and a semiconductor element separate from each other prior to said superposing step.

51. The method of claim 21 further comprising the step of providing a metallic element and a semiconductor element separate from each other prior to said superposing step.