TREA

Method for diffusion soldering

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Information

  • Patent Application
  • 20070205253
  • Publication Number
    20070205253
  • Date Filed
    March 06, 2006
    18 years ago
  • Date Published
    September 06, 2007
    16 years ago
Information
Abstract
A method for connecting at least two metal layers by means of a diffusion soldering process, wherein each of the metal layers that is to be connected is plated with a respective solder layer prior to the diffusion soldering process.
Description

BRIEF DESCRIPTION OF THE DRAWING FIGURES

The invention will now be described in more detail with reference to the accompanying drawings in which:



FIG. 1 illustrates the connection of two metal layers by means of a conventional diffusion soldering process;



FIG. 2 illustrates the connection of two metal layers by means of a diffusion soldering process according to one exemplary embodiment of the present invention;



FIG. 3 shows a flow chart illustrating methods according to the invention for connecting two metal layers by means of a diffusion soldering process;



FIG. 4 shows a top view of a first embodiment according to the present invention having primary and secondary pads;



FIG. 5 is a graph illustrating the forces acting on pads of different diameters due to displacement from a given solder thickness; and



FIG. 6 shows a top view of a second embodiment according to the invention having primary and secondary pads.


Claims
  • 1. A method for connecting at least two metal layers by means of a diffusion soldering process comprises the step of: plating each of the metal layers that is to be connected with a respective solder layer prior to performing the diffusion soldering process.
  • 2. The method according to claim 1, wherein the metal layers are self-aligned with respect to each other during the diffusion soldering process by means of forces due to surface tension in the molten solder joining the metal layers.
  • 3. The method according to claim 2, wherein the forces due to the surface tension are increased by increasing the wettability of the molten solder.
  • 4. The method according to claim 3, wherein the step of performing the diffusion soldering process comprises performing the diffuse soldering process free of any external mechanical pressure being exerted on the metal layers during the process.
  • 5. The method according to claim 4, comprising the step of: heating the solder in the solder layers only once above the melting point of the solder.
  • 6. The method according to claim 5, comprising the step of: heating the solder after placing the solder layers in contact with each other and aligning them with respect to each other.
  • 7. The method according to claim 7, comprising the step of: arranging a diffusion barrier layer between at least one of the metal layers and its respective solder layer.
  • 8. The method according to claim 1, wherein the metal layers comprise at least one of copper, silver, gold and palladium.
  • 9. The method according to claim 1, wherein the solder layers comprise at least one of tin, silver, indium, gallium, bismuth, gold and copper.
  • 10. The method according to claim 1, comprising the step of: outgassing the solder layers before soldering at a partial pressure of formic acid in one of an inert gas atmosphere and in a vacuum.
  • 11. The method according to claim 10, wherein the outgassing step comprises: performing the outgassing at a temperature lower than the melting point of the solder.
  • 12. The method according to claim 11, wherein the partial pressure of the formic acid is 20 to 100 mbar.
  • 13. The method according to claim 8, wherein the outgassing step comprises: performing the outgassing for two to three minutes.
  • 14. The method according to claim 10, comprising the step of: heating the metal layers and the solder layers, during the diffusion soldering process, at such a rate that all of the solder of the solder layers is in a molten state for at least some time.
  • 15. The method according to claim 14, wherein the heating step comprises: heating the metal layers and the solder layers at an increased atmospheric pressure to a temperature above the melting point of the solder.
  • 16. The method according to claim 15, wherein the atmosphere contains gaseous flux material in an inert gas.
  • 17. The method according to claim 16, wherein the gaseous flux material is at least one of atomic hydrogen, molecular hydrogen, carbon monoxide, ammonia and formic acid.
  • 18. The method according to claim 14, wherein the heating step comprises: heating the metal layers and the solder layers to a temperature above the melting point of the solder in a vacuum with a partial pressure of formic acid of 20 to 100 mbar.
  • 19. The method according to claim 1, comprising the step of: arranging the metal layers on carriers and patterned to form at least one pad.
  • 20. The method according to claim 19, further including the step of: patterning the solder layers in the same shape as the respective metal layers.
  • 21. The method according to claim 19, further including the step of: patterning the solder layers in a shape different from the respective metal layers.
  • 22. The method according to claim 21, wherein the step of patterning the solder layers comprises the step of: patterning the solder layers by means of a solder resist.
  • 23. The method according to claim 22, wherein the step of patterning the solder layers including the step of: patterning of the solder resist on metal layers facing each such that the metal layers are symmetrical with respect to each other.
  • 24. The method according to claim 19, comprising the step of: covering the side walls of the at least one pad with a layer that is not wettable by the molten solder.
  • 25. The method according to claim 19, wherein the pads of metal layers that are facing each other are structured symmetrically with respect to each other.
  • 26. The method according to claim 25, wherein the pads comprise primary pads and secondary pads, wherein the secondary pads are larger in area than the primary pads, and at least one primary pad is arranged between at least two secondary pads.
  • 27. The method according to claim 26, comprising the step of: arranging the secondary pads in such a manner that the sum of the hydrostatic forces in the secondary pads to each side of the primary pads is equal.
  • 28. The method according to claim 25, wherein the pads comprise primary pads and secondary pads, wherein the secondary pads are larger in area than the primary pads, and at least one secondary pad is arranged between at least two primary pads.
  • 29. The method according to claim 28, comprising the step of: arranging the secondary pads in such a manner that the sum of the hydrostatic forces in the primary pads to each side of the secondary pads is equal.
  • 30. The method according to claim 26, wherein the primary pads have diameters smaller than 30 μm, and the secondary pads have diameters greater than 30 μm.
  • 31. The method according to claim 26, wherein during the diffusion soldering process, the hydrostatic pressure in the secondary pads is used to apply pressure to the molten solder between the primary pads.
  • 32. The method according to claim 19, wherein the carriers comprise wafers and substrates of electronic components.
  • 33. A mechanical connection for connecting at least two metal layers by means of a diffusion soldering process, wherein each of the metal layers that is to be connected is plated with a respective solder layer.
  • 34. The connection according to claim 33, wherein a diffusion barrier layer is arranged between at least one of the metal layers and its respective solder layer.
  • 35. The connection according to claim 34, wherein the metal layers comprise at least one of copper, silver, gold and palladium.
  • 36. The connection according to claim 35, wherein the solder layers comprise at least one of tin, silver, indium, gallium, bismuth, gold and copper.
  • 37. The connection according to claim 33, wherein the metal layers are arranged on carriers and patterned to form at least one pad.
  • 38. The connection according to claim 37, wherein at least one pad is selected from the group consisting of: a seal ring, a stress relief of the primary contacts, a heat sink, an electromagnetic shield, a wiring plane, and an alignment mark.
  • 39. The connection according to claim 37, wherein the side walls of the at least one pad are covered with a layer that is not wettable by the molten solder.
  • 40. The connection according to claim 37, wherein the pads of metal layers that are facing each other are structured symmetrically with respect to each other.
  • 41. The connection according to claim 37, wherein leveling elements are placed between at least two pads of at least one metal layer, wherein the leveling elements have the same thickness as the metal layer and fill the gap between the two pads.
  • 42. The connection according to claim 41, wherein the leveling elements are electrically insulating and non-wettable by the solder.
  • 43. The connection according to claim 37, wherein the pads comprise primary pads and secondary pads, wherein the secondary pads are larger in area than the primary pads, and at least one primary pad is arranged between at least two secondary pads.
  • 44. The connection according to claim 37, wherein the pads comprise primary pads and secondary pads, wherein the secondary pads are larger in area than the primary pads, and at least one secondary pad is arranged between at least two primary pads.
  • 45. The connection according to claim 43, wherein the primary pads have diameters smaller than 30 μm, and the secondary pads have diameters greater than 30 μm.
  • 46. The connection according to claim 37, wherein the carriers comprise wafers and substrates of electronic components.
  • 47. The connection according to claim 46, wherein the primary pads are electrical connections to electrical elements in the wafers and substrates.
  • 48. A layered structure to be exposed to a diffusion soldering process to form a joined structure comprising: a first substrate having a first metal layer formed thereon according to a first pattern to define a plurality of first pads;a second substrate having a second metal layer formed thereon according to a second pattern to define a plurality of second pads;a first solder layer plated on the first metal layer according to the first pattern;a second solder layer plated on the second metal layer according to the second pattern; andmeans associated with sidewalls of at least one of the first and second metal layers for preventing molten solder from attaching to the sidewalls;wherein the first and second substrates are arranged by placing the first and second solder layers in an abutting relationship for joining the first and second substrates together by the diffusion soldering process.
  • 49. The layered structure of claim 48, wherein the means comprises a non-wettable layer that is disposed on the sidewalls.
  • 50. The layered structure of claim 48, further comprising: a plurality of leveling elements disposed between at least one of the first pads and the second pads, the leveling elements being formed of an electrically insulating material that is non-wettable by molten solder for preventing solder from the pads from attaching to the leveling elements and thereby bridge the pads.