FRETTING AND WHISKER RESISTANT COATING SYSTEM AND METHOD

• US 20090017327A1
• Filed: 06/24/2008
• Published: 01/15/2009
• Est. Priority Date: 10/14/2003
• Status: Active Grant

• Current Assignee: Wieland Rolled Products North America, LLC
• Original Assignee: GBC Metals LLC (Schwenk Donau GmbH & Company KG)
• Inventors: Robinson, Peter W., Chen, Szuchain F., Gerfen, John E., Lasiuk, Nicole A., Khan, Abid A.
• Granted Patent: US 7,808,109 B2
• Time in Patent Office: Days
• US Class Current: 428/632
• CPC Class Codes: C23C 28/021 including at least one metal alloy layer
• CPC Class Codes: C23C 28/023 only coatings of metal elements only
• CPC Class Codes: C23C 28/025 with at least one zinc-based layer
• CPC Class Codes: C23C 28/321 with at least one metal alloy layer
• CPC Class Codes: C23C 28/322 only coatings of metal elements only
• CPC Class Codes: C23C 28/3225 with at least one zinc-based layer
• CPC Class Codes: C23C 28/345 with at least one oxide layer
• CPC Class Codes: C23C 28/3455 with a refractory ceramic layer, e.g. refractory metal oxide, ZrO2, rare earth oxides or a thermal barrier system comprising at least one refractory oxide layer
• CPC Class Codes: C23C 28/347 with layers adapted for cutting tools or wear applications
• CPC Class Codes: C25D 5/10 Electroplating with more than one layer of the same or of different metals for bearings C25D7/10
• CPC Class Codes: C25D 5/12 at least one layer being of nickel or chromium
• CPC Class Codes: C25D 5/617 Crystalline layers
• CPC Class Codes: C25D 5/627 Electroplating characterised by the visual appearance of the layers, e.g. colour, brightness or mat appearance
• CPC Class Codes: H01L 2224/11849 Reflowing
• CPC Class Codes: H01L 2224/119 Methods of manufacturing bump connectors involving a specific sequence of method steps
• CPC Class Codes: H01L 2224/45015 being circular
• CPC Class Codes: H01L 2224/451 with a principal constituent of the material being a metal or a metalloid, e.g. boron (B), silicon (Si), germanium (Ge), arsenic (As), antimony (Sb), tellurium (Te) and polonium (Po), and alloys thereof
• CPC Class Codes: H01L 2224/45139 Silver (Ag) as principal constituent
• CPC Class Codes: H01L 2224/48247 connecting the wire to a bond pad of the item
• CPC Class Codes: H01L 2224/49171 Fan-out arrangements
• CPC Class Codes: H01L 23/49582 : Metallic layers on lead frames
• 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 24/49 : of a plurality of wire connectors
• 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 2924/01012 : Magnesium [Mg]
• CPC Class Codes: H01L 2924/01019 : Potassium [K]
• CPC Class Codes: H01L 2924/0102 : Calcium [Ca]
• CPC Class Codes: H01L 2924/01025 : Manganese [Mn]
• CPC Class Codes: H01L 2924/01046 : Palladium [Pd]
• CPC Class Codes: H01L 2924/01063 : Europium [Eu]
• CPC Class Codes: H01L 2924/01078 : Platinum [Pt]
• CPC Class Codes: H01L 2924/01079 : Gold [Au]
• CPC Class Codes: H01L 2924/01322 : Eutectic Alloys, i.e. obtained by a liquid transforming into two solid phases
• CPC Class Codes: H01L 2924/01327 : Intermediate phases, i.e. intermetallics compounds
• CPC Class Codes: H01L 2924/14 : Integrated circuits
• CPC Class Codes: H01L 2924/181 : Encapsulation
• CPC Class Codes: H01L 2924/207 : Diameter ranges
• CPC Class Codes: H01L 2924/2075 : larger or equal to 1 micron less than 10 microns
• CPC Class Codes: H01R 13/03 : characterised by the material, e.g. plating, or coating materials
• CPC Class Codes: H05K 3/244 : Finish plating of conductors, especially of copper conductors, e.g. for pads or lands selective plating methods H05K3/243; finish plating of conductors made by printing techniques H05K3/246; solder as finish H05K3/3457, e.g. by plating H05K3/3473
• CPC Class Codes: Y10T 428/1259 : Oxide
• CPC Class Codes: Y10T 428/12611 : Oxide-containing component
• CPC Class Codes: Y10T 428/12715 : Next to Group IB metal-base component
• CPC Class Codes: Y10T 428/12896 : Ag-base component

Abstract

A coated electrically conductive substrate has particular utility where there are multiple closely spaced leads and tin whiskers constitute a potential short circuit. Such substrates include leadframes, terminal pins and circuit traces such as on printed circuit boards and flexible circuits. This electrically conductive substrate has a plurality of leads separated by a distance capable of bridging by a tin whisker, a silver or silver-base alloy layer coating at least one surface of at least one of the plurality of leads, and a fine grain tin or tin-base alloy layer directly coating said silver layer.

An alternative coated electrically conductive substrate has particular utility where debris from fretting wear may oxidize and increase electrical resistivity, such an in a connector assembly. This electrically conductive substrate has a barrier layer deposited on the substrate that is effective to inhibit diffusion of constituents the substrate into a plurality of subsequently deposited layers. The subsequently deposited layers include a sacrificial layer deposited on the barrier layer that is effective to form intermetallic compounds with tin, a low resistivity oxide metal layer deposited on said sacrificial layer, and an outermost layer of tin or a tin-base alloy directly deposited on the low resistivity oxide metal layer.

In this alternative embodiment, the barrier layer is preferably nickel or a nickel-base alloy and the low resisitivity oxide metal layer is preferably silver or a silver-base alloy.

When heated, the coated substrate of this second embodiment forms a unique structure having a copper or copper-base alloy substrate, an intervening layer formed from a mixture or metals including copper and tin, and an outermost layer which is a mixture of a copper-tin intermetallic containing phase and a silver-rich phase. It is believed that this silver-rich phase is particularly beneficial to reduce an increase in resistivity due to oxidation of fretting wear debris.

Claims

1-20. -20. (canceled)

21. An electrically conductive material coated with a plurality of layers, comprising:

an electrically conductive substrate;

a barrier layer deposited on said substrate effective to inhibit diffusion of constituents said substrate to said plurality of layers;

a sacrificial layer deposited on said barrier layer effective to form intermetallic compounds with tin;

a low resistivity oxide metal layer deposited on said sacrificial layer; and

an outermost layer of tin or a tin-base alloy directly deposited on said low resistivity oxide metal layer.

23. The electrically conductive material of claim 21 wherein said barrier layer is selected from the group consisting of nickel, cobalt, iron, manganese, chromium, molybdenum and alloys thereof.

24. The electrically conductive material of claim 23 wherein said barrier layer has a thickness of from 4 microinches to 40 microinches.

25. The electrically conductive material of claim 24 wherein said barrier layer is nickel or a nickel-base alloy.

26. The electrically conductive material of claim 25 wherein said nickel or nickel-base alloy barrier layer has a thickness of from 4 microinches to 20 microinches.

27. The electrically conductive material of claim 25 wherein said sacrificial layer is copper or a copper-base alloy.

28. The electrically conductive material of claim 27 wherein said copper or copper-base alloy sacrificial layer has a thickness of from 2 microinches to 60 microinches.

29. The electrically conductive material of claim 28 wherein said copper or copper-base alloy sacrificial layer has a thickness of from 4 microinches to 20 microinches.

30. The electrically conductive material of claim 28 wherein said low resistivity oxide metal layer is selected from the group silver, indium, iron, zinc, niobium, rhenium, ruthenium, vanadium, gold, platinum, palladium and alloys thereof.

31. The electrically conductive material of claim 30 wherein said low resistivity oxide metal layer has a thickness of from 5 microinches to 40 microinches.

32. The electrically conductive material of claim 31 wherein said low resistivity oxide metal layer is silver or a silver-base alloy,

33. The electrically conductive material of claim 32 wherein said silver or silver-base alloy layer has a thickness of from 5 microinches to 20 microinches.

34. The electrically conductive material of claim 32 wherein said outermost layer of tin or a tin-base alloy has an average grain size in excess of 0.5 millimeter.

22. (canceled)

35. An electrical connector assembly including a socket and a probe, with at least one of said socket or probe comprising:

an electrically conductive substrate;

a barrier layer deposited on said substrate effective to inhibit diffusion of constituents said substrate to said plurality of layers;

a sacrificial layer deposited on said barrier layer effective to from intermetallic compounds with tin;

a low resistivity oxide metal layer deposited on said sacrificial layer; and

an outermost layer of tin or a tin-base alloy directly deposited on said low resistivity oxide metal layer.

37. The electrically conductive material of claim 35 wherein said barrier layer is selected from the group consisting of nickel, cobalt, iron, manganese, chromium, molybdenum and alloys thereof.

38. The electrically conductive material of claim 37 wherein said barrier layer has a thickness of from 4 microinches to 40 microinches.

39. The electrically conductive material of claim 38 wherein said barrier layer is nickel or a nickel-base alloy.

40. The electrically conductive material of claim 39 wherein said sacrificial layer is copper or a copper-base alloy.

41. The electrically conductive material of claim 40 wherein said copper or copper-base alloy sacrificial layer has a thickness of from 2 microinches to 60 microinches.

42. The electrically conductive material of claim 41 wherein said low resistivity oxide metal layer is selected from the group silver, indium, iron, zinc, niobium, rhenium, ruthenium, vanadium, gold, platinum, palladium and alloys thereof.

43. The electrically conductive material of claim 42 wherein said low resistivity oxide metal layer has a thickness of from 4 microinches to 40 microinches.

44. The electrically conductive material of claim 43 wherein said low resistivity oxide metal layer is silver or a silver-base alloy.

45. The electrically conductive material of claim 44 wherein said outermost layer of tin or a tin-base alloy has an average grain size in excess of 0.5 millimeter.

36. (canceled)

46. A composite structure comprising:

a copper or copper-base alloy substrate;

an intervening layer formed from a mixture of metals including copper and tin; and

an outermost layer which is a mixture of a copper-tin intermetallic containing phase and a silver-rich phase.

47. The composite structure of claim 46 wherein said copper-tin intermetallic containing phase further contains silver.

48. The composite structure of claim 47 wherein said silver-rich phase further contains copper and tin.

49. The composite structure of claim 48 wherein a thin layer of free tin or free tin-base alloy overlies said outermost layer.

50. The composite structure of claim 49 wherein said thin layer has a thickness of from 2 microinches to 20 microinches.

51. A method for the manufacture of a tin whisker resistant coating, comprising the steps of:

(a) providing a substrate having a plurality of spaced electrically conductive leads separated by a distance capable of being bridged by a tin whisker;

(b) coating at least a portion of said leads with a layer of silver or a silver-base alloy; and

(c) directly coating said layer of silver or silver-base alloy with a layer of fine grain tin or tin-base alloy.

52. The method of claim 51 wherein said electrically conductive leads each have an inner portion, a mid-portion and an outer portion and at least said outer portion is coated with from 1 microinch to 120 microinches of silver or a silver-base alloy by a process selected from the group consisting of electroplating and immersion plating.

53. The method of claim 52 wherein said silver or silver-base alloy is directly coated with from 0.006 microinch to 400 microinches of tin by electroplating.

54. The method of claim 53 wherein said substrate is formed into a leadframe having a die paddle centrally disposed from said inner portions of said leads and said die paddle and said inner portions are coated with silver or a silver base alloy prior to step (b).

55. The method of claim 54 wherein said die paddle and inner lead portions are encapsulated in a polymer resin prior to step (b).

56. The method of claim 55 wherein said mid-portion of said leads is substantially free of silver or a silver-base alloy coating when encapsulated in said polymer resin.

57. A method for the manufacture of a component resistant to a fretting wear debris induced increase is resistivity, comprising the steps of:

(a) coating an electrically conductive substrate with a barrier layer effective to prevent the diffusion of constituent of said conductive substrate therethrough at an anticipated service temperature of said component;

(b) coating said barrier layer with a sacrificial layer that is effective to form an intermetallic with an outermost coating layer of said component;

(c) coating said sacrificial layer with a low resistivity oxide metal or metal alloy layer;

(d) directly coating said low resistivity oxide metal or metal alloy layer with an outermost layer having a melting temperature less than a melting temperature of any one of said electrically conductive substrate, said barrier layer, said sacrificial layer, and said low resistivity oxide metal or metal alloy layer; and

(e) heating said coated electrically conductive substrate to a temperature effective to melt and reflow said outermost layer.

58. The method of claim 57 wherein prior to step (a) said electrically conductive substrate is coated with a layer of copper.

59. The method of claim 58 wherein said barrier layer is selected from the group consisting of nickel, cobalt, iron, manganese, chromium, molybdenum and alloys and mixtures thereof.

60. The method of claim 59 wherein said barrier is selected to be nickel or a nickel-base alloy deposited by electroplating.

61. The method of claim 60 wherein said sacrificial layer is selected to be copper or a copper-base alloy.

62. The method of claim 61 wherein said low resistivity oxide metal layer is selected from the group consisting of silver, indium, iron, niobium, rhenium, ruthenium, vanadium, gold, platinum, palladium and zinc.

63. The method of claim 62 wherein said low resistivity oxide metal layer is selected to be silver or a silver-base alloy deposited by a method selected from the group consisting of electroplating and immersion plating to a thickness of from 1 microinch to 120 microinches.

64. The method of claim 63 wherein steps (d) and (e) are combined into a single step such as a hot air leveled tin (HALT) process.

65. The method of claim 63 wherein said outermost layer is tin or a tin-base alloy deposited by electroplating.

66. The method of claim 65 wherein either before or after step (e), said coated electrically conductive substrate is heated to a temperature below the melting temperature of said tin or tin-base alloy to reduce the thickness of free tin.

67. The method of claim 66 wherein said heating to a temperature below the melting temperature of said tin or tin-base alloy is effective to reduce the thickness of free tin to from 2 microinches to 20 microinches.

68. The method of claim 64 including forming said coated electrically conductive substrate into both a socket component and a probe component of a connector assembly.

69. The method of claim 67 including forming said coated electrically conductive substrate into both a socket component and a probe component of a connector assembly.