Contact structures with porous networks for solder connections, and methods of fabricating same
A contact pad includes a solder-wettable porous network ( 310 ) which wicks the molten solder ( 130 ) and thus restricts the lateral spread of the solder, thus preventing solder bridging between adjacent contact pads.
1. An assembly comprising:
a first contact pad of a first microelectronic component, the first contact pad comprising a porous network;
a second contact pad of a second microelectronic device, the second contact pad bonded to the first contact pad via a solder at least partly disposed in pores of the porous network; and
a film deposited on pores of the porous network, the film comprising titanium, nickel, or copper in a thickness of 2-5 nm.
2. The assembly of claim 1 , wherein the porous network comprises gold or a gold alloy.
3. The assembly of claim 1 , wherein the first contact pad comprises an open-pore sponge with 70-80% porosity.
4. The assembly of claim 1 , wherein the porous network comprises pore sizes from 15 nm to 360 nm.
5. The assembly of claim 1 , wherein both the first contact pad and the second contact pad comprise porous networks.
6. The assembly of claim 5 , wherein the solder penetrates at least 15 nm into each of the first contact pad and the second contact pad.
7. The assembly of claim 1 , wherein the solder has been diffusion bonded to the porous network via thermocompression bonding.
8. The assembly of claim 7 , wherein the solder that has been diffusion bonded to the porous network of the first contact pad contains indium and has a melting temperature below 180° C.
9. A contact pad resistant to solder-bridges between adjacent contact pads, for making a microelectronic component with contact pads at fine pitch, comprising:
a gold alloy at a bonding interface of the microelectronic component;
a wicking layer of the gold alloy comprising a porous network, the wicking layer comprising pores with diameters between 15-360 nm to absorb a solder at least 15 nm into the contact pad via capillary action; and
a film deposited on pores of the porous network, the film comprising titanium, nickel, or copper in a thickness of 2-5 nm for increasing a wettability of the porous network for absorbing excess solder.
10. The contact pad of claim 9 , wherein the wicking surface of the layer of gold alloy is at least partly pre-loaded with the solder before bonding with another conductor at the bonding interface.
11. The contact pad of claim 10 , wherein the wicking surface is at least partly pre-loaded with the solder, wherein the solder comprises a low melting point alloy containing indium.
12. The contact pad of claim 9 , wherein the wicking layer comprises an open-pore sponge with 70-80% porosity.
13. The contact pad of claim 12 , wherein the open-pore sponge of the wicking layer has a capacity to absorb a volume of excess solder up to 70-80% of a volume of the wicking layer itself.
14. A die for microelectronics, comprising:
a substrate;
a contact pad on the substrate;
a layer of the contact pad etched into a porous sponge; and
pores of the porous sponge comprising a diameter between 15-360 nm; and
a film of titanium, nickel, or copper in a thickness of 2-5 nm lining pores of the porous sponge for increasing a wettability of the porous sponge for absorbing a solder.
15. The die of claim 14 , wherein the porous sponge has a porosity of 70-80% for absorbing a solder.
16. The die of claim 14 , wherein the porous sponge is tinned with a solder.
17. The die of claim 14 , wherein the porous sponge comprises gold or a gold alloy.