Systems and methods for high aspect ratio flip-chip interconnects
Interconnect and/or reflow methods of the present disclosure achieve high aspect ratio interconnects, for example interconnects having an aspect ratio as high as 4, in addition to wider interconnect height tolerances among interconnects (for example, interconnects having a height variability of up to about 30%) while still achieving reliable electrical connections. Moreover, flip-chip interconnects configured in accordance with principles of the present disclosure can provide improved z-axis spacing between die-to-die and/or die-to-substrate flip chip stacks, for example z-axis spacing as large as 600 μm. In this manner, additional spacing can be achieved for MEMS devices and/or similar components that are extendable and/or deformable out of the die plane.
1. A method for forming electronic interconnects, the method comprising:
dipping a needle into a metal epoxy to cover the tip of the needle with the metal epoxy;
retrieving the needle from the metal epoxy with a small amount of the metal epoxy on the tip of the needle;
moving the needle close to a bond pad to cause the metal epoxy to attach to the bond pad; and
moving the needle away from the bond pad to leave a bump of metal epoxy on the bond pad.
2. The method of claim 1 , further comprising repeating the dipping the needle, retrieving the needle, moving the needle close to the bond pad, and moving the needle away from the bond pad to increase an aspect ratio of the bump of metal epoxy.
3. The method of claim 1 , wherein the bond pad is less than 100 μm by 100 μm in size, and wherein the bump does not extend more than 25 μm beyond an edge of the bond pad.
4. The method of claim 2 , wherein the bond pad is 100 μm by 100 μm in size, and wherein the bump of the metal epoxy has a height exceeding 110 μm.
5. A method for forming electronic interconnects, the method comprising:
moving a dispensing tip within 50 μm of the surface of a bond pad;
dispensing solder paste from the dispensing tip;
moving the dispensing tip away from the bond pad to leave a bump of solder paste on the bond pad; and
repeating the moving the dispensing tip, dispensing solder paste, and moving the dispensing tip away from the bond pad to increase the aspect ratio of the bump of solder paste.
6. The method of claim 5 , wherein the bump has an aspect ratio greater than one after reflowing.
7. The method of claim 5 , wherein flux residue extends no more than 50 μm from an edge of the bond pad after reflowing.
8. A method for forming electronic interconnects, the method comprising:
selecting a first surface, wherein the first surface is not a bond pad;
moving a dispensing tip within 50 μm of the first surface;
dispensing solder paste from the dispensing tip via a first pulse;
moving the dispensing tip away from the first surface while dispensing solder paste from the dispensing tip, to form a rod of solder paste extending from and attached to the dispensing tip;
moving the dispensing tip to bring the rod of solder paste in contact with a bond pad; and
moving the dispensing tip away from the bond pad to leave a bump of solder paste on the bond pad.
9. The method of claim 8 , wherein the bump of solder paste has an aspect ratio greater than two prior to reflowing.
10. The method of claim 8 , wherein the bump of solder paste has an aspect ratio greater than three prior to reflowing.
11. The method of claim 9 , further comprising reflowing the solder paste to form an interconnect, wherein flux residue extends no more than 50 μm from an edge of the bond pad after the reflowing.
12. A method for reflowing solder paste, the method comprising:
forming a bump of solder paste on a bond pad; and
heating the bump to a temperature exceeding a melting temperature of the solder paste over a period between 60 minutes and 80 minutes,
wherein the heating causes the bump of solder paste to increase in temperature at a rate between 1.6 degrees Celsius per minute and 2.4 degrees Celsius per minute,
wherein the bump of solder paste has an aspect ratio greater than one after the heating, and
wherein flux residue extends no more than 50 μm from an edge of the bond pad after the heating.
13. The method of claim 12 , wherein the heating changes the height of the bump of solder paste by less than 40 percent.