Solder bump, flip chip structure and method for preparing the same

A flip chip structure, comprising:

• a substrate;
• a bond pad formed on the substrate;
• a passivation layer formed on the substrate and surrounding the bond pad;
• a first solder bump formed on the bond pad and an adjacent portion of the passivation layer;
• and
• a second solder bump formed on a portion of the passivation layer and spaced apart from the first solder bump;
• wherein the first solder bump includes a first pillar formed on the bond pad and the adjacent portion of the passivation layer and extending in a vertical direction, a first coated layer fittingly formed on the first pillar, and a first solder ball formed on the first coated layer;
• wherein the second solder bump includes a second pillar formed on the portion of the passivation layer and extending in the vertical direction, a second coated layer fittingly formed on the second pillar, and a second solder ball formed on the second coated layer;
• wherein the first pillar includes a depression formed in a shape of an inverted cone and formed on a top surface of the first pillar;
• and
• a top surface of the first coated layer is rougher than a bottom surface of the first coated layer.

A method for preparing a flip chip structure, comprising:

• providing a substrate;
• forming a bond pad on the substrate;
• forming a passivation layer on the substrate, wherein the passivation layer surrounds the bond pad;
• sputtering a seed layer on the bond pad and the passivation layer;
• and
• simultaneously forming a first solder bump on a part of the seed layer that corresponds in position to the bond pad and an adjacent portion of the passivation layer, and a second solder bump on another part of the seed layer that corresponds in position to a portion of the passivation layer;
• wherein the second solder bump is spaced apart from the first solder bump;
• wherein the first solder bump includes a first pillar formed on the part of the seed layer and extending in a vertical direction, a first coated layer fittingly formed on the first pillar, and a first solder ball formed on the first coated layer;
• wherein the second solder bump includes a second pillar formed on another part of the seed layer and extending in the vertical direction, a second coated layer fittingly formed on the first pillar, and a second solder ball formed on the second coated layer;
• and
• wherein the first pillar includes a depression formed in the shape of an inverted cone and formed in a top surface of the first pillar.