Bumps comprising tin, cooper and bismuth for liquid metal socket interconnects

1 . An apparatus comprising:

a substrate comprising:

electrical contacts on a first side of the substrate to couple the substrate to an integrated circuit die;

a passivation layer on a second side of the substrate opposite the first side, the passivation layer defining a plurality of openings exposing the second side of the substrate;

metal pads on the second side of the substrate and within the openings defined by the passivation layer; and

solder bumps on the metal pads, the solder bumps comprising an intermetallic compound (IMC) resistant to Gallium-based liquid metal embrittlement, wherein the IMC comprises Tin and Copper and the solder bumps comprise between 20-40% Tin, 20-40% Copper, and 20-40% Bismuth.

2 . The apparatus of claim 1 , wherein the metal pads are positioned on the second side of the substrate such that trenches are defined between the metal pads and the passivation layer.

3 . The apparatus of claim 1 , further comprising an integrated circuit die coupled to the substrate on the first side of the substrate.

4 . The apparatus of claim 3 , further comprising:

a thermal interface material on the integrated circuit die; and

a cap coupled to the second side of the substrate, wherein the integrated circuit die and the thermal interface material are between the cap and the second side of the substrate.

5 . The apparatus of claim 1 , further comprising:

an interposer coupled to the substrate on the second side of the substrate, the interposer comprising:

a housing defining a set of holes;

an adhesive layer on a first side of the housing, the adhesive layer in contact with the passivation layer;

a barrier layer on a second side of the housing opposite the first side, the barrier layer enclosing the holes on the second side of the housing; and

Gallium-based liquid metal within the holes and in contact with the solder bumps.

6 . A system comprising:

a main board;

a socket coupled to the main board, the socket comprising a set of pins extending from the socket in a direction opposite the main board;

a package coupled to the socket, the package comprising:

a substrate;

an integrated circuit die on a first side of the substrate;

metal pads on a second side of the substrate opposite the first side;

solder bumps on the metal pads, the solder bumps comprising an intermetallic compound (IMC) resistant to Gallium-based liquid metal embrittlement, wherein the IMC comprises Tin and Copper and the solder bumps comprise between 20-40% Tin, 20-40% Copper, and 20-40% Bismuth; and

an interposer comprising a Gallium-based liquid metal in each of a set of reservoirs defined within the interposer, the Gallium-based liquid metal in each reservoir in contact with a respective solder bump;

wherein the pins of the socket are within the reservoirs of the interposer and in contact with the Gallium-based liquid metal.

7 . The system of claim 6 , wherein the substrate further comprises a passivation layer on the second side of the substrate, the passivation layer defining a plurality of trenches between the metal pads and the second side of the substrate.

8 . The system of claim 6 , wherein the package further comprises:

a thermal interface material on the integrated circuit die; and

a cap coupled to the second side of the substrate, wherein the integrated circuit die and the thermal interface material are between the cap and the second side of the substrate.

9 . An apparatus comprising:

a substrate comprising:

electrical contacts on a first side of the substrate to couple the substrate to an integrated circuit die;

a dielectric layer on a second side of the substrate opposite the first side, the dielectric layer defining a plurality of openings exposing the second side of the substrate;

metal pads on the second side of the substrate and within the openings defined by the dielectric layer; and

solder bumps on the metal pads, the solder bumps comprising an intermetallic compound (IMC) comprising Tin and Copper and further comprising Bismuth, wherein the solder bumps comprise between 20-40% Tin, 20-40% Copper, and 20-40% Bismuth.

10 . The apparatus of claim 9 , wherein the metal pads are positioned on the second side of the substrate such that trenches are defined between the metal pads and the dielectric layer.

11 . The apparatus of claim 9 , further comprising an integrated circuit die coupled to the substrate on the first side of the substrate.

12 . The apparatus of claim 9 , further comprising an interposer comprising a Gallium-based liquid metal in each of a set of reservoirs defined within the interposer, wherein each solder bump is in contact with the Gallium-based liquid metal in a reservoir of the interposer.

13 . A product made by a process comprising:

forming a substrate;

forming electrical contacts on a first side of the substrate;

forming a passivation layer on a second side of the substrate opposite the first side;

forming openings in the passivation layer exposing the second side of the substrate;

forming metal pads on the second side of the substrate within the openings in the passivation layer;

depositing solder paste on the metal pads, the solder paste comprising Tin, Copper, and Bismuth, wherein the solder paste comprises between 20-40% Tin, 20-40% Copper, and 20-40% Bismuth; and

exposing the solder paste to gas comprising Nitrogen and heat to form an intermetallic compound comprising Tin and Copper.

14 . The product of claim 13 , wherein exposing the solder paste to heat comprises exposing the solder paste to a temperature between 180-250° C.

15 . The product of claim 13 , wherein the process further comprises coupling an integrated circuit die to the first side of the substrate;

depositing a thermal interface material on the integrated circuit die; and

attaching a cap to the first side of the substrate such that the integrated circuit die and the thermal interface material are between the cap and the substrate;

wherein the solder paste is deposited after coupling the integrated circuit die to the substrate.