Method for Fabricating Equal Height Metal Pillars of Different Diameters

1 . A method comprising the steps of:

A) providing, a wafer having a plurality of flip-chip devices, each flip-chip device having a plurality of die pads thereon;

B) depositing a first layer of photoresist on the wafer;

C) patterning the first layer of photoresist to form a first plurality of openings therein, each of the first openings having a first diameter and exposing a first set of die pads;

D) plating metal into the first openings to form a first metal pillar in each of the first openings for a first time period;

E) patterning the first layer of photoresist to form a second plurality of openings therein, each of the second openings having a second diameter and exposing a second set of die pads; and

F) plating metal into the first and second openings for a second time period to add to each of the metal pillars in the first openings and form a metal pillar in each of the second openings;

wherein the first diameter is greater than the second diameter, the first set of die pads is different from the second set of die pads, and the first and second time periods and plating conditions are chosen such that, after step F) each of the pillars in the second openings has substantially the same height as a pillars in each of the first openings.

2 . The method of claim 1 wherein the plated metal is copper.

3 . The method of claim 1 further comprising the steps of:

G) plating, after step F), solder into the first and second openings to form a solder layer in each of the openings and on exposed ends of the metal pillars;

H) depositing a second layer of photoresist to at least cover the second openings in the first photoresist layer; and

I) plating solder into the first openings to form a second solder layer in each of the first openings and on the first solder layer therein.

4 . The method of claim 3 wherein each of the metal pillars of the first and second plurality of metal pillars has a height above a die pad and each of the solder layers has a height above its respective metal pillar, and a ratio of the height of a metal pillar to the height of its respective solder layer is 1:10 to 100:1.

5 . The method of claim 4 wherein the height of each of the metal pillars is 20 to 70 microns, the height of each solder layers is 10 to 60 microns, and the first and second diameters range from 20 to 80 microns.

6 . The method of claim 4 wherein a sum of the height of each of the metal pillars and its respective solder layer is between 5 microns and 130 microns and the first and second diameters range from substantially 5 to 150 microns.

7 . The method of claim 4 wherein the first diameter is less than 80 microns and the second diameter is greater than 80 microns, and a sum of the height of each metal pillar and its respective solder layer is 80 microns or less.

8 . The method of claim 3 wherein in step H) comprises the steps of:

depositing a second layer of photoresist covering the first photoresist layer;

patterning the second photoresist layer form a plurality of openings therein, the openings having a diameter substantially equal to the first diameter and exposing the solder layers in the first openings of the first photoresist layer.

9 . The method of claim 1 further comprising the step of:

depositing, before step B), a conductive layer over the plurality of die pads;

wherein in steps D) and G) the plating is by electroplating using the conductive layer as a electroplating electrode.

10 . The method of claim 9 wherein the conductive layer comprises a barrier layer and a strike layer deposited over the barrier layer.

11 . The method of claim 10 wherein the barrier comprises titanium and the strike layer comprises copper.

12 . The method of claim 1 further comprising the step of removing, after step F), the first photoresist layer.

13 . A method of claim 12 further comprising the steps of:

singulating the wafer to separate the plurality of a flip-chip devices into individual devices;

selecting one of the singulated devices;

providing a substrate having a plurality of substrate pads, each of the plurality of substrate pads positioned on the substrate to align with a respective one of the metal pillars of the first and second plurality of metal pillars on the selected flip-chip device;

bringing the selected flip-chip device in proximity to the substrate such that all the plurality of substrate pads positioned on the substrate are aligned with a respective one of the metal pillars on the selected flip-chip device; and

bonding the metal pillars to their respective substrate pads using solder to form a package.

14 . The method of claim 13 wherein the flip-chip device comprises a material selected from the group consisting of silicon, gallium arsenide, indium phosphide, and a combination thereof and wherein the substrate is selected from the group consisting of glass-epoxy, polytetrafluoroethylene, ceramic, silicon, glass, and a combination thereof.

15 . The method of claim 13 further comprising the steps of:

forming, after the bonding step, an underfill layer between the flip-chip device and the substrate; and

forming, after forming the underfill layer, an overmold on the flip-chip device and the substrate.

16 . A method comprising the steps of:

A) providing a wafer having a plurality of flip-chip devices, each flip-chip device having a plurality of die pads thereon;

B) depositing a first layer of photoresist on the wafer;

C) patterning the first layer of photoresist to form a first plurality of openings therein, each of the first openings having a first diameter and exposing a first set of die pads;

D) plating metal into the first plurality of openings to form a first metal pillar in each of the first plurality of openings, each of the first metal pillars having substantially the first diameter and a first height above its respective die pad;

E) patterning the first layer of photoresist to form a second plurality of openings therein, each of the second openings having a second diameter and exposing a second set of die pads; and

F) plating metal into the first and second openings and onto the first metal pillars and exposed second set of die pads, respectively, to form a second metal pillar in each of the first openings and a metal pillar in each of the second openings, each of the metal pillars in the second openings having substantially the second diameter and a height above its respective die pad, and each of the second pillars in the first plurality of openings having substantially the first diameter and a height above its respective first metal pillar;

wherein the first diameter is greater than the second diameter, a sum of the first and second pillar heights in each of the first openings is substantially equal to the height of the metal pillar in each of the second openings, and the first set of die pads is different from the second set of die pads.

17 . The method of claim 16 wherein each of the copper pillars of the first and second plurality of copper pillars has a height above a die pad and each of the solder layers has a height above its respective copper pillar, and the height of each of the copper pillars is 20 to 70 microns, the height of each solder layers is 10 to 60 microns, a sum of the height of each copper pillar and its respective solder layer is 80 microns or less, and the first diameter is less than 80 microns and the second diameter is greater than 80 microns.

18 . The method of claim 16 wherein each of the copper pillars of the first and second plurality of copper pillars has a height above a die pad and each of the solder layers has a height above its respective copper pillar, and a sum of the height of each of the copper pillars and its respective solder layer is between 5 microns and 130 microns and the first and second diameters range from substantially 5 to 150 microns.

19 . The method of claim 16 wherein the barrier comprises titanium and the strike layer comprises copper.

20 . The method of claim 15 further comprising the steps of:

forming, after the bonding step, an underfill layer between the flip-chip device and the substrate; and

forming, after forming the underfill layer, an overmold on the flip-chip device and the substrate.