Solder joint reliability in microelectronic packaging
A microelectronic assembly and method for fabricating the same are described. In an example, a microelectronic assembly includes a microelectronic device having a surface with one or more areas to receive one or more solder balls, the one or more areas having a surface finish comprising Ni. A solder material comprising Cu, such as flux or paste, is applied to the Ni surface finish and one or more solder balls are coupled to the microelectronic device by a reflow process that forms a solder joint between the one or more solder balls, the solder material comprising Cu, and the one or more areas having a surface finish comprising Ni.
1. A method comprising:
providing a first microelectronic device having a surface with a first area to receive a solder ball;
applying a first nickel-based surface finish comprising Ni and P to the first area;
applying, to the nickel-based surface finish, at least one of a first flux including about 0.1-2 weight % Cu or a first solder paste including about 0.5-2weight % Cu;
depositing the solder ball onto the first area, the first area having the applied first nickel-based surface finish and the applied paste or flux; and
reacting the solder with the Ni and P in the nickel-based surface finish and with the Cu in the first paste or first flux during a reflowing of the solder ball to couple the solder to the first microelectronic device.
2. A method according to claim 1 , further comprising:
providing a second microelectronic device having a surface with a second area to receive the solder ball;
applying a copper-based surface finish comprising Cu to the second area;
applying, to the copper-based surface finish, at least one of a second flux comprising about 0.1-2 weight % Ni or a second solder paste comprising about 0.1-2 weight % Ni;
positioning the first microelectronic device such that the solder ball is in substantial alignment and adjacent to the second area; and
reacting the solder with the Cu in the copper-based surface finish and with the Ni in the second paste or flux during a reflowing of the solder ball to couple the second microelectronic device to the first microelectronic device.
3. A method according to claim 1 , further comprising:
providing a second microelectronic device having a surface with a second area to receive the solder ball;
applying a second nickel-based surface finish comprising Ni and P to the second area;
applying, to the nickel-based surface finish, at least one of a second flux including about 0.1-2 weight % Cu or a second solder paste comprising about 0.5-2 weight % Cu;
positioning the first microelectronic device such that the solder ball is in substantial alignment and adjacent to the second area; and
reacting the solder with the Ni and P in the nickel-based surface finish and with the Cu in the second paste or flux during a reflowing of the solder ball to couple the second microelectronic device to the first microelectronic device.
4. A method according to claim 1 , wherein applying the first flux or the first paste comprises applying a first flux and wherein the first flux includes activators, polymers, thickeners, thixotropic agents, solvents, and Cu particles in amounts ranging from about 0.1% to 2% by weight.
5. A method according to claim 1 , wherein applying the first flux or the first paste comprises applying a first solder paste and wherein the first paste includes activators, polymers, thickeners, thixotropic agents, solvents, and solder powder, wherein the solder powder Cu content ranges from about 0.5% to 2% by weight.
6. A method according to claim 2 , wherein applying the second flux or the second paste comprises applying a second flux including activators, polymers, thickeners, thixotropic agents, solvents, and Ni particles in amounts ranging from about 0.1% to 2% by weight.
7. A method according to claim 2 , wherein the first microelectronic device is a package substrate and the second microelectronic device is a circuit board.
8. A method according to claim 2 , wherein the first microelectronic device is an integrated circuit die and the second microelectronic device is a package substrate.
9. A method comprising:
providing a first microelectronic device having a surface with a first area to receive a solder ball;
applying a first copper-based surface finish comprising Cu to the first area;
applying, to the copper-based surface finish, at least one of a first flux comprising about 0.1-2 weight % Ni or a first solder paste including a solder powder comprising about 0.1-2 weight % Ni;
depositing the solder ball onto the first area, the first area having the applied first surface finish and the applied paste or flux; and
reacting the solder with the Cu in the first copper-based surface finish and with the Ni in the first paste or first flux during a reflowing of the solder ball to couple the solder to the first microelectronic device.
10. A method according to claim 9 , further comprising:
providing a second microelectronic device having a surface with a second area to receive the solder ball;
applying a second copper-based surface finish comprising Cu to the second area;
applying, to the second copper-based surface finish, at least one of a second flux comprising about 0.1-2 weight % Ni or a second solder paste including a solder powder comprising about 0.1-2 weight % Ni;
positioning the first microelectronic device such that the solder ball is in substantial alignment and adjacent to the second area; and
reacting the solder with the Cu in the second copper-based surface finish and with the Ni in the second paste or second flux during a reflowing of the solder ball to couple the second microelectronic device to the first microelectronic device.
11. A method according to claim 9 , further comprising:
providing a second microelectronic device having a surface with a second area to receive the solder ball;
applying a nickel-based surface finish comprising Ni and P to the second area;
applying, to the nickel-based surface finish, at least one of a second flux including about 0.1-2 weight % Cu or a second solder paste comprising about 0.5-2 weight % Cu;
positioning the first microelectronic device such that the solder ball is in substantial alignment and adjacent to the second area; and
reacting the solder with the Ni and P in the nickel-based surface finish and with the Cu in the second paste or second flux during a reflowing of the solder ball to couple the second microelectronic device to the first microelectronic device.
12. A method comprising:
providing a first microelectronic device having a surface with a first area to receive a solder ball;
applying a first copper-based surface finish comprising Cu to the first area;
applying a solderable material, comprising Ni particles in amounts ranging from about 0.1% to 2% by weight, to the surface of the solder ball to form a solderable surface material on the solder ball, wherein the solder ball comprises solder having a different amount of Ni than that of the solderable surface material;
depositing the solder ball onto the first area, the first area having the applied first copper-based surface finish;
reacting the solder with the Ni in the solderable surface material and with the Cu in the copper-based surface finish during a reflowing of the solder ball to couple the solder to the first microelectronic device.
13. A method according to claim 12 further comprising:
providing a second microelectronic device having a surface with a second area to receive the solder ball;
applying a second copper-based surface finish comprising Cu to the second area;
positioning the first microelectronic device such that the solder ball is in substantial alignment and adjacent to the second area of the second microelectronic device; and
reacting the solder with the Ni in the solderable surface material and with the Cu in the second copper-based surface finish during a reflowing of the solder ball to couple the second microelectronic device to the first microelectronic device.
14. A method according to claim 12 , wherein the solder ball comprises solder substantially free of Ni.
15. A method according to claim 1 , wherein the solder ball comprises a solder having a different weight % Cu than that of the paste or flux.
16. A method according to claim 15 , wherein the solder ball comprises a solder having a lower weight % Cu than that of the paste or flux.
17. A method according to claim 1 , wherein the solder ball comprises solder substantially free of Cu.
18. A method according to claim 1 , wherein the first nickel-based surface finish comprises at least at about 90 wt % Ni and at least about 5 wt % P.
19. A method according to claim 9 , wherein the first copper-based surface finish comprises 100 wt % copper.