Method of forming solder bumps
A method of forming solder bumps includes preparing a substrate having a surface on which a plurality of electrode pads are formed, forming a resist layer on the substrate, the resist layer having a plurality of openings, each of the openings being aligned with a corresponding electrode pad of the plurality of electrode pads, forming a conductive pillar in each of the openings of the resist layer, forming conductive layers to cover at least side walls of the resist layer in the openings to block gas emanating from the resist layer, filling molten solder in each of the openings in which the conductive layers has been formed and removing the resist layer.
1. A solder bump structure comprising:
a free-standing metal pillar formed directly on an electrode pad;
a conductive layer disposed directly on the metal pillar over the electrode pad, the conductive layer including a sintered conductive paste formulated to form a cone-shaped top surface determined by volume shrinkage during sintering and dependent on dimensions of a solder bump, a planar bottom surface and a sidewall substantially perpendicular to the planar bottom surface; and
a solder formed on the cone-shaped top surface of the conductive layer, the solder having a convex top surface.
2. The solder bump structure according to claim 1 , wherein the solder is in contact with and extends an entire length of the cone-shaped top surface of the conductive layer.
3. The solder bump structure according to claim 1 , wherein the conductive layer comprises at least a metal with solder wettability higher than materials of the solder.
4. The solder bump structure according to claim 1 , wherein the conductive layer comprises at least a metal with a higher melting point than materials of the solder.
5. The solder bump structure according to claim 1 , wherein the conductive layer comprises at least one material selected from the group consisting of Cu, Ni, Ag, Pd and Au.
6. The solder bump structure according to claim 1 , wherein at least one seed layer is formed between the metal pillar and the electrode pad.
7. The solder bump structure according to claim 1 , wherein the conductive layer comprises a thickness that blocks outgas during soldering.
8. The solder bump structure according to claim 1 , wherein the conductive layer comprises at least a first conductive layer and a second conductive layer formed on the first conductive layer;
the first conductive layer includes a material having a melting point that exceeds that of the materials of the solder; and
the second conductive layer includes a material having a higher solder wettability than the solder.
9. The solder bump structure according to claim 1 , wherein the conductive layer comprises a composition ratio of metals having the same composition ratio of metals present in the solder.
10. A solder bump structure comprising:
a free-standing conductive pillar formed directly on at least one seed layer, the at least one seed layer formed on an electrode pad, wherein the electrode pad is formed in an insulating layer;
a conductive layer directly on the conductive pillar over the electrode pad, the conductive layer including a sintered conductive paste formulated to form a concave surface determined by volume shrinkage during sintering and dependent on dimensions of a solder bump, a planar bottom surface and a sidewall substantially perpendicular to the planar bottom surface; and
a solder formed on the surface of the conductive layer, the solder having a convex top surface.
11. The solder bump structure according to claim 10 , wherein the solder is in contact with and extends an entire length of the surface of the conductive layer.
12. The solder bump structure according to claim 10 , wherein the conductive layer comprises at least a metal with solder wettability higher than materials of the solder.
13. The solder bump structure according to claim 10 , wherein the conductive layer comprises at least a metal with a higher melting point than materials of the solder.
14. The solder bump structure according to claim 10 , wherein the conductive layer comprises at least one material selected from the group consisting of Cu, Ni, Ag, Pd and Au.
15. The solder bump structure according to claim 10 , wherein the conductive layer comprises at least one layer formed by a metal formation technique including at least one of vacuum deposition, sputtering, electrolessplating or plasma chemical vapor deposition.
16. The solder bump structure according to claim 10 , wherein the conductive layer comprises a thickness that blocks outgas during soldering.
17. The solder bump structure according to claim 10 , wherein the conductive layer comprises at least a first conductive layer and a second conductive layer formed on the first conductive layer;
the first conductive layer includes a material having a melting point that exceeds that of the materials of the solder; and
the second conductive layer includes a material having a higher solder wettability than the materials of the solder.
18. The solder bump structure according to claim 10 , wherein the conductive layer comprises a composition ratio of metals having the same composition ratio of metals present in the solder.