Method of building solder bumps

A method of forming a solder bump having a defined height on a layer of solder-wettable under bump metallurgy which is positioned upon a contact pad which is in turn positioned upon a layer of substrate material and wherein the contact pad is surrounded and bordered by a dielectric passivation surface layer upon the substrate material, and wherein the passivation surface layer is non-wettable by solder;

• the method comprising:
• (a) forming a layer of solder soluble metal of a predetermined size area upon the layer of solder-wettable under bump metallurgy and upon a portion of the surrounding passivation layer with the predetermined size area of the layer of solder soluble metal being greater than the area of the under bump metallurgy;
• (b) coating the layer of solder soluble metal with a deposit of liquid solder while substantially avoiding complete dissolution of the solder soluble metal by the solder so that the solder entirely covers the solder soluble metal and those portions of the passivation layer covered by the solder soluble metal, and with the solder having a composition which does not wet the passivation layer so that the area coated with solder is defined by the predetermined size area of the layer of solder soluble metal and where the volume of coated solder is determined by the soldering conditions;
• (c) solidifying the deposit of liquid solder;
• (d) reheating the solidified deposit of solder to a liquid state and until the layer of solder soluble metal substantially completely dissolves in the liquid solder and the liquid solder forms a droplet of solder which substantially covers only the layer of solder-wettable under bump metallurgy and which has retreated from the non-wettable passivation surface layer, so that the height of the resulting solder bump is defined by the volume of solder deposited and the predetermined size area of the under bump metallurgy;
• and
• (e) solidifying the resulting solder bump.

A method of forming a self-aligned solder bump having a predetermined selected height on a substrate, the method comprising:

• (a) forming a layer of solder-wettable under bump metallurgy having a predetermined size area on a contact pad and wherein the contact pad is upon a semiconductor material and is surrounded on the semiconductor material by a layer of dielectric surface passivation material upon the semiconductor material, and wherein the dielectric passivation material is non-wettable by solder;
• (b) covering the layer of solder-wettable under bump metallurgy and a portion of the surrounding passivation layer with a layer of a solder soluble metal having a predetermined size area which is larger than the predetermined size area of the layer of under bump metallurgy;
• (c) coating the layer of solder soluble metal with liquified solder for a time sufficient to substantially wet the solder soluble metal with solder, but insufficient to substantially completely dissolve the solder soluble metal to dissolve in the liquid solder, such that the volume of solder deposited upon the layer of solder soluble metal is defined by the predetermined sixe area of the layer of solder soluble metal and a wetting angle formed between the dielectric passivation material and the liquid solder;
• (d) solidifying the solder;
• (e) reheating the solder to liquid solder for a time sufficient for the solder soluble metal to substantially completely dissolve in the liquid solder so that the liquid solder retreats from the larger predetermined size area that was defined by the solder soluble metal to the smaller predetermined size area of the solder-wettable under bump metallurgy, and thereby forms a solder bump which is correspondingly higher than the coating of solder that was on the layer of solder soluble metal, and for which the height is defined by the predetermined size area of the under bump metallurgy and the volume of solder that was coated upon the layer of solder soluble metal;
• and
• (f) solidifying the defined solder bump.

A method of aligning solder on a substrate, the method comprising:

• (a) forming a layer of solder-wettable under bump metallurgy on a contact pad and wherein the contact pad is upon a semiconductor material and is surrounded on the semiconductor material by a layer of dielectric surface passivation material upon the semiconductor material, and wherein the passivation material is non-wettable by solder;
• (b) covering the layer of solder-wettable under bump metallurgy and a portion of the surrounding passivation layer with a layer of a solder soluble metal having a predetermined size area which is larger than the area of the layer of under bump metallurgy;
• and
• (c) coating the layer of solder soluble metal with liquified solder for a time sufficient to substantially wet the solder soluble metal with solder, but insufficient to substantially completely dissolve the solder soluble metal in the liquid solder, such that the volume and alignment of solder deposited upon the layer of solder soluble metal is defined by the predetermined size area of the layer of solder soluble metal and the wetting angle formed between the passivation material and the liquid solder.

A method of aligning a solder bump on a substrate, the method comprising:

• (a) aligning a metal contact pad on the surface of a semiconductor material;
• (b) surrounding the contact pad with a layer of dielectric surface passivation material which is non-wettable to solder so that the perimeter of the contact pad touches the dielectric surface passivation material;
• (c) forming a layer of solder-wettable under bump metallurgy having a predetermined size area on the contact pad and wherein the under bump metallurgy substantially covers the contact pad;
• (d) covering the layer of solder-wettable under bump metallurgy with a layer of solder soluble metal having a predetermined size area which is larger than the predetermined size area of the layer of under bump metallurgy and which extends onto the dielectric surface passivation material surrounding the contact pad;
• (e) coating the layer of solder soluble metal with liquified solder for a time sufficient to substantially wet the solder soluble metal with solder, but insufficient to substantially completely dissolve the solder soluble metal in the liquid solder, such that the area and alignment of solder deposited upon the layer of solder soluble metal is defined by the predetermined size area of the layer of solder soluble metal rather than by the area of the under bump metallurgy;
• (f) solidifying the solder;
• (g) reheating the solder to liquid solder for a time sufficient for the solder soluble metal to substantially completely dissolve in the liquid solder so that the liquid solder retreats form the larger predetermined size area that was defined by the solder soluble metal to the smaller predetermined size area of the solder-wettable under bump metallurgy, and thereby forms an aligned solder bump upon the under bump metallurgy, with the size and alignment of the solder bump being defined by the predetermined size area of the solder-wettable under bump metallurgy;
• and
• (h) solidifying the defined solder bump.