Pillar bump formed using spot-laser
A pillar bump, such as a copper pillar bump, is formed on an integrated circuit chip by applying a metallic powder over a conductive pad on a surface of the chip. The metallic powder is selectively spot-lasered to form the pillar bump. Any remaining unsolidified metallic powder may be removed from the surface of the chip. This process may be repeated to increase the bump height. Further, a solder cap may be formed on an outer surface of the pillar bump.
1. A method for forming an electrically conductive pillar bump on a conductive pad of an integrated circuit chip, the method comprising:
(a) applying a metallic powder over an active surface of the chip and the conductive pad;
(b) selectively applying a spot-laser to the metallic powder to form at least one solid metallic element;
(c) removing un-solidified metallic powder from the surface of the chip; and
(d) forming a solder cap on an outer surface of the at least one solid metallic element to thereby form the pillar bump.
2. The method of claim 1 , wherein:
the method further comprises forming, before step (a), a solid under-bump metallization (UBM) layer over the conductive pad;
in step (a), the metallic powder is applied over the UBM layer; and
in step (b), the at least one solid metallic element is formed on the UBM layer.
3. The method of claim 2 , wherein forming the UBM layer comprises:
applying a UBM powder over a surface of the chip such that the UBM powder covers the conductive pad;
forming the solid UBM layer by at least one of melting and sintering the UBM powder; and
removing un-solidified UBM powder from the surface of the chip.
4. The method of claim 2 , wherein step (d) comprises:
applying a solder powder over a surface of the chip such that the solder powder covers the at least one solid metallic element;
forming the solder cap on the outer surface of the at least one solid metallic element by at least one of melting and sintering the solder powder; and
removing un-solidified solder powder from the surface of the chip.
5. The method of claim 1 , wherein step (d) comprises:
applying a solder powder over a surface of the chip such that the solder powder covers the at least one solid metallic element;
forming the solid solder cap on the outer surface of the at least one solid metallic element by at least one of melting or sintering the solder powder; and
removing un-solidified solder powder from the surface of the chip.
6. The method of claim 1 , wherein step (d) comprises plating a solder cap onto the outer surface of the at least one solid metallic element.
7. The method of claim 1 , wherein step (b) further comprises:
applying the metallic powder over the surface of the chip and the at least one solid metallic element;
selectively applying a spot-laser to the metallic powder to form at least one other solid metallic element on the at least one solid metallic element.
8. The method of claim 1 , wherein step (b) comprises performing at least one of selective-laser sintering (SLS) and selective-laser melting (SLM).
9. A pillar bump formed in accordance with the method recited in claim 1 .