Method of forming conductive bumps
A sealing layer is provided on the surface of a substrate such as a semiconductor wafer. The sealing layer includes apertures which expose external contact locations for semiconductor dice formed on the wafer. Solder paste is deposited in the apertures and reflowed to form discrete conductive elements for attachment of the electronic devices to higher level circuit structures. The wafer is then divided or “singulated” to provide individual semiconductor dice having their active surfaces covered by the sealing layer. In this manner, the sealing layer initially acts as a stencil for forming the discrete conductive elements and subsequently forms a chip scale package structure to protect the semiconductor dice from the environment.
1. A method of forming an electronic device package comprising:
providing a substrate bearing at least one electronic device;
providing at least one external contact location on a surface of the substrate;
forming a mask layer over the surface of the substrate and surrounding the at least one external contact location;
forming a sealing layer over the mask layer with an aperture exposing the at least one external contact location and also exposing a portion of the mask layer surrounding the at least one external contact location;
depositing a conductive material within the aperture exposing the at least one external contact location; and
forming the conductive material into a discrete conductive element attached to the at least one external contact location and extending outwardly from the surface of the substrate to a distance beyond the sealing layer.
2. The method of claim 1 , wherein providing a substrate comprises providing a semiconductor substrate having at least one bond pad for electrical communication with the at least one electronic device.
3. The method of claim 2 , wherein providing the at least one external contact location on a surface of the substrate comprises:
forming the mask layer to surround a portion of the at least one bond pad; and
forming the sealing layer over the mask layer with an aperture exposing the at least one bond pad and a portion of the mask layer surrounding the portion of the at least one bond pad.
4. The method of claim 2 , further comprising forming at least one layer of metal over the at least one bond pad.
5. The method of claim 4 , wherein providing the at least one external contact location on a surface of the substrate comprises:
forming the mask layer to surround a portion of the at least one layer of metal located substantially directly over the at least one bond pad; and
forming the sealing layer over the mask layer with an aperture exposing the portion of the at least one layer of metal and a portion of the mask layer surrounding the portion of the at least one layer of metal.
6. The method of claim 4 , wherein providing the at least one external contact location on a surface of the substrate comprises:
forming the mask layer to surround a portion of the at least one layer of metal at a location distant from the at least one bond pad; and
forming the sealing layer over the mask layer with an aperture exposing the portion of the at least one layer of metal and a portion of the mask layer surrounding the portion of the at least one layer of metal.
7. The method of claim 2 , wherein providing a substrate comprises providing a semiconductor wafer bearing a plurality of electronic devices, each electronic device of the plurality of electronic devices having at least one external contact location; and wherein forming a sealing layer further comprises forming the sealing layer over an active surface of the semiconductor wafer with a plurality of apertures to expose the at least one external contact location of each electronic device through the sealing layer.
8. The method of claim 7 , further comprising providing another sealing layer over a back surface of the semiconductor wafer.
9. The method of claim 7 , further comprising reducing a thickness of the semiconductor wafer prior to depositing the conductive material within the aperture exposing the at least one external contact location.
10. The method of claim 9 , wherein reducing a thickness of the semiconductor wafer comprises abrasively removing material from a back surface of the semiconductor wafer.
11. The method of claim 7 , further comprising at least partially dividing the semiconductor wafer along lines passing between the plurality of electronic devices to provide at least one individual semiconductor dice.
12. The method of claim 11 , further comprising forming at least another sealing layer on a surface of the at least one individual semiconductor die exposed while at least partially dividing the semiconductor wafer.
13. The method of claim 1 , further comprising forming the aperture of the sealing layer with a perimeter defined by one of a rectangular shape, a circular shape, a teardrop shape and an elliptical shape.
14. The method of claim 1 , wherein depositing a conductive material within the aperture exposing the at least one external contact location comprises depositing a solder paste comprised of particles of at least one metal suspended in a flux material.
15. The method of claim 14 , wherein forming the conductive material into a discrete conductive element comprises:
heating the particles of the at least one metal in the solder paste to a molten state;
forming the molten at least one metal substantially into a spherical shape wetted onto the at least one external contact location; and
cooling the molten at least one metal to form a solidified volume of the at least one metal.
16. The method of claim 15 , further comprising providing a support layer proximate a base portion of the discrete conductive element from a residual portion of the flux material within the aperture exposing the at least one external contact location at least partially surrounding a base portion of the solidified volume of the at least one metal.
17. The method of claim 1 , further comprising forming the mask layer and the sealing layer as a substantially homogenous unitary structure.
18. The method of claim 17 , wherein forming the mask layer and the sealing layer as a substantially homogenous unitary structure comprises forming the substantially homogeneous unitary structure as a plurality of superimposed layers of sequentially cured material.
19. The method of claim 1 , wherein forming the sealing layer comprises forming the sealing layer of a plurality of superimposed layers of sequentially cured liquid material.
20. The method of claim 19 , wherein forming a plurality of superimposed layers of sequentially cured liquid material comprises:
selectively curing a first volume of liquid material with an activating agent to form a first layer of the plurality of superimposed layers of cured material; and
selectively curing at least a second volume of liquid material with the activating agent to form at least a second layer of the plurality of superimposed layers of cured material.
21. The method of claim 20 , wherein forming a plurality of superimposed layers of sequentially cured liquid material comprises forming the plurality of superimposed layers from a photocurable material.
22. The method of claim 19 , wherein forming the mask layer comprises forming the mask layer of one or more of superimposed layers of sequentially cured liquid material.
23. The method of claim 19 , further comprising forming the plurality of superimposed layers of sequentially cured liquid material in accordance with a computer-generated model of the sealing layer.
24. The method of claim 1 , further comprising forming the sealing layer of a polymer material.