ENGINEERED MATERIALS FOR ELECTRONICS ASSEMBLY

Abstract

A solder material for use in electronic assembly, the solder material comprising: solder layers; and a core layer comprising a core material, the core layer being sandwiched between the solder layers, wherein: the thermal conductivity of the core material is greater than the thermal conductivity of the solder.

Claims

1-28. (canceled)

29. A solder material for use in electronic assembly, the solder material comprising: solder layers; and a core layer comprising a core material, the core layer being sandwiched between the solder layers, wherein: the thermal conductivity of the core material is greater than the thermal conductivity of the solder.

30. The solder material of claim 29, wherein the core material has a thermal conductivity of greater than or equal to 65 W/m.Math.K.

31. The solder material of claim 29, wherein the melting point of the core material is greater than the reflow temperature of the solder.

32. The solder material of claim 29, wherein the thickness of the core layer is from 100 to 500 μm.

33. The solder material of claim 29, wherein the thickness of each solder layer is from 25 to 150 μm.

34. The solder material of claim 29, wherein the core material comprises a metal and/or an alloy.

35. The solder material of claim 29, wherein the core material comprises one or more of: copper, silver, nickel, molybdenum, beryllium, cobalt, iron, copper-tungsten alloy, nickel-silver alloy, copper-zinc alloy and copper-nickel-zinc alloy.

36. The solder material of claim 29, wherein the solder is lead-free.

37. The solder material of claim 29, wherein the solder comprises one or more of: In, SnIn alloy, SnBi alloy, BiIn alloy, AgIn alloy, SnAg alloy, SnCu alloy, InGa alloy, SnBiAgCu alloy, SnBiZn alloy, SnInAg alloy, SnBiAgCuIn alloy, SnZn alloy, SnCuInGa alloy, SnCuAg alloy, SnAgSb alloy and SnCuSb alloy.

38. The solder material of claim 29, wherein the core material comprises copper and the solder comprises Sn-20In-2Ag alloy; and/or wherein the solder material is in the form of a foil, a strip, a film, a ribbon or a preform.

39. The solder material of claim 29, wherein the core is completely coated with the solder; and/or wherein the solder material has an effective thermal conductivity of greater than 65 W/m.Math.K.

40. A solder joint comprising the solder material of claim 29.

41. An interconnect comprising the solder material of claim 29.

42. An IGBT, MOSFET, LED or microprocessor comprising the solder material of any of claim 29 or a solder joint comprising the solder material, or an interconnect comprising the solder material.

43. Use of the solder material of claim 29 in a soldering method selected from Surface Mount Technology (SMT) soldering, die attach soldering, thermal interface soldering, hand soldering, laser and RF induction soldering, and thermos-sonic soldering; or for die-attach (Level I), substrate attach (Level II) or package to heatsink attach (Level III).

44. A method of forming a solder joint comprising: providing the solder material of claim 29 in the vicinity of two or more work pieces to be joined, and heating the solder material to form a soldered joint, preferably wherein the two or more work pieces to be joined comprise: a device or die and a substrate, or a substrate and a printed circuit board (PCB), or a printed circuit board and a heatsink.

45. A method of manufacturing the solder material of claim 29, the method comprising: providing two of more layers of solder, providing a layer of core material, and laminating the layers of solder on either side of the layer of core material.

46. The method of claim 45, wherein the layer of core material is in the form of a ribbon and/or the layer of solder is in the form of a ribbon, preferably wherein the ribbons are provided by casting, extrusion or drawing; and/or wherein the layers are laminated in a co-drawing process, preferably a high-pressure co-drawing process; and/or wherein the laminated layers are diced and/or stamped.

47. A method of manufacturing the solder material of claim 29, the method comprising: providing a layer of core material, and coating the core material with solder.

48. The method of claim 47, wherein the surface of the layer of core material is cleaned prior to it being coated with the solder; and/or wherein coating the core material with solder comprises contacting the core material with a molten solder bath.

Description

[0074] The invention will now be described in relation to the following non-limiting drawings in which:

[0075] FIG. 1 shows a schematic of the assembly of a typical electronic device.

[0076] FIG. 2 shows cross-sectional schematics of alternative arrangements of the solder material according to the present invention.

[0077] FIG. 3 shows a microscopy image of a cross section of a solder material according to the present invention.

[0078] FIG. 2 shows a cross-sectional view of two types of solder material according to the present invention. The solder materials comprise a core layer 9 sandwiched between solder layers 10. The solder material shown in the top picture has solder only at the top and at the bottom side. There is no solder on the sides. The other solder material has solder on all sides of the core.

[0079] The invention will now be described in relation to the following non-limiting examples.

EXAMPLE 1

[0080] A solder material (preform) was prepared by a high-pressure lamination process. FIG. 3 shows a microscopy image of a cross section of the preform. The central core is 300 μm thick and formed of copper. The solder on both sides is Sn20% In2% Ag. The solder thickness varies from 50 to 100 μm. The effective thermal conductivity of this sample is about 130 W/m.Math.K, measured by a nano-flash transient measurement technique.

EXAMPLE 2

[0081] A number of preforms were prepared in a similar manner to Example 1 but with varying thicknesses of the core (Keff=400 W/m.Math.K) and solder layers (Keff=54 W/m.Math.K). The thermal performance of the preforms was evaluated. Table 1 shows estimated thermal resistances and equivalent thermal conductivities. The thermal resistance of the hick interfaces is much lower (equivalent Keff is much higher) as compared to solder alone.

TABLE-US-00001 TABLE 2 Selected examples of Cu-core preforms with their estimated thermal resistance and equivalent thermal conductivity. Core Solder Thermal Equivalent Length Width thickness thickness on Resistance Keff (mm) (mm) (mm) each side (C/W) (W/m .Math. K) 10 10 0.2 0.1 0.0420 95.2 10 10 0.2 0.05 0.0235 127.6 10 10 0.3 0.1 0.0445 112.3 10 10 0.3 0.05 0.0260 153.7 10 10 0.4 0.1 0.0470 127.6 10 10 0.4 0.05 0.0285 175.3

[0082] The invention will now be further described with reference to the following numbered clauses:

1. A solder material comprising: [0083] a core comprising a core material; and [0084] solder at least partially coating the core.
2. The solder material of clause 1 for use in electronic assembly.
3. The solder material of clause 1 or clause 2, wherein the core is in the form of a layer.
4. The solder material of clause 3, wherein the thickness of the core layer is from 100 to 500 μm, preferably from 200 to 400 μm, more preferably from 150 to 300 μm.
5. The solder material of clause 3 or clause 4, wherein solder is in the form of layers, and wherein the core is sandwiched between two solder layers.
6. The solder material of clause 6, wherein the thickness of the solder layer is from 25 to 150 μm, preferably from 50 to 100 μm.
7. The solder material of any preceding clause in the form of a foil, a strip, a film, a ribbon or a preform.
8. The solder material of any preceding clause, wherein the melting point of the core material is greater than the reflow temperature of the solder.
9. The solder material of any preceding clause, wherein the thermal conductivity of the core material is greater than the thermal conductivity of the solder.
10. The solder material of clause 9, wherein the core material has a thermal conductivity of greater than or equal to 65 W/m.Math.K, preferably greater than 65 w/m.Math.K, more preferably greater than 70 W/m.Math.k, even more preferably greater than 75 W/m.Math.K.
11. The solder material of any preceding clause, wherein the core material comprises a metal and/or an alloy.
12. The solder material of any preceding clause, wherein the core material comprises one or more of: copper, silver, nickel, molybdenum, beryllium, cobalt, iron, copper-tungsten alloy, nickel-silver alloy, copper-zinc alloy and copper-nickel-zinc alloy.
13. The solder material of any preceding clause, wherein the solder is lead-free.
14. The solder material of any preceding clause, wherein the solder comprises one or more of: In, SnIn alloy (e.g. 5-58% Sn, 42-95% In), SnBi alloy (e.g. 42-60% Sn, 40-58% Bi), BiIn alloy (e.g. 5-67% Bi, 33-95% In), AgIn alloy (e.g. 3% Ag, 97% In), SnAg alloy (e.g. 90-97.5% Sn, 2.5-10% Ag), SnCu alloy (e.g. 99.3-99.6% Sn, 0.4-0.7% Cu), InGa alloy (e.g. 99.3-99.5% In, 0.5-0.7% Ga), SnBiAgCu alloy (e.g. 50% Sn, 47% Bi, 1% Ag, 2% Cu), SnBiZn alloy (e.g. 65.5% Sn, 31.5% Bi, 3% Zn), SnInAg alloy (e.g. 77.2% Sn, 20% In, 2.8% Ag), SnBiAgCuIn alloy (e.g. 82.3% Sn, 2.2% Bi, 3% Ag, 0.5% Cu, 12% In), SnZn alloy (e.g. 91% Sn, 9% Zn), SnCuInGa alloy (e.g. 92.8% Sn, 0.7% Cu, 6% In, 0.5% Ga), SnCuAg alloy (e.g. 95.5% Sn, 3.8% Ag, 0.7% Cu), SnAgSb alloy (e.g. 95% Sn, 3.5% Ag, 1.5% Sb) and SnCuSb alloy (e.g. 4-95% Sn, 1-2% Cu, 4% Sb).
15. The solder material of any preceding clause, wherein the core material comprises copper and the solder comprises Sn-20In-2Ag alloy.
16. The solder material of any preceding clause, wherein the core and the solder are in the form of layers, and wherein the solder layers are coated on either side of the core layer.
17. The solder material of clause 16, wherein the thickness of the core layer is from 100 to 500 μm, preferably from 200 to 400 μm, more preferably from 150 to 300 μm.
18. The solder material of clause 16 or clause 17, wherein the thickness of the solder layer is from 25 to 150 μm, preferably from 50 to 100 μm.
19. The solder material of any preceding clause, wherein the core is completely coated with the solder.
20. The solder material of any preceding clause having an effective thermal conductivity of greater than 65 W/m.Math.K, preferably greater than 80 W/m.Math.K, more preferably greater than 100 W/m.Math.K, even more preferably greater than 130 W/m.Math.K.
21. Use of the solder material of any preceding clause in a soldering method selected from Surface Mount Technology (SMT) soldering, die attach soldering, thermal interface soldering, hand soldering, laser and RF induction soldering, and thermos-sonic soldering.
22. Use of the solder material of any of clauses 1 to 20 for die-attach (Level I), substrate attach (Level II) or package to heatsink attach (Level III).
23. An interconnect comprising the solder material of any of clauses 1 to 20.
24. An IGBT, MOSFET, LED or microprocessor comprising the solder material of any of clauses 1 to 20, or the interconnect of clause 23.
25. A method of forming a solder joint comprising: [0085] providing the solder material of any of clauses 1 to 20 in the vicinity of two or more work pieces to be joined, and [0086] heating the solder material to form a soldered joint.
26. A method of manufacturing the solder material of any of clauses 1 to 20, the method comprising: [0087] providing two of more layers of solder, [0088] providing a layer of core material, and [0089] laminating the layers of solder on either side of the layer of core material.
27. The method of clause 26, wherein the layer of core material is in the form of a ribbon and/or the layer of solder is in the form of a ribbon.
28. The method of clause 27, wherein the ribbons are provided by casting, extrusion or drawing.
29. The method of any of clauses 26 to 28, wherein the layers are laminated in a co-drawing process, preferably a high-pressure co-drawing process.
30. The method of any of clauses 26 to 29, wherein the laminated layers are diced and/or stamped.
31. A method of manufacturing the solder material of any of clauses 1 to 20, the method comprising: [0090] providing a layer of core material, and [0091] coating the core material with solder.
32. The method of clause 31, wherein surface of the layer of core material is cleaned prior to it being coated with the solder.
33. The method of clause 31 or clause 33, wherein coating the core material with solder comprises passing the core material through a molten solder bath.

[0092] The foregoing detailed description has been provided by way of explanation and illustration, and is not intended to limit the scope of the appended claims. Many variations in the presently preferred embodiments illustrated herein will be apparent to one of ordinary skill in the art and remain within the scope of the appended claims and their equivalents.