Conductive ink for filling vias
Vias (holes) are formed in a wafer or a dielectric layer. A low viscosity conductive ink, containing microscopic metal particles, is deposited over the top surface of the wafer to cover the vias. An external force is applied to urge the ink into the vias, including an electrical force, a magnetic force, a centrifugal force, a vacuum, or a suction force for outgassing the air in the vias. Any remaining ink on the surface is removed by a squeegee, spinning, an air knife, or removal of an underlying photoresist layer. The ink in the vias is heated to evaporate the liquid and sinter the remaining metal particles to form a conductive path in the vias. The resulting wafer may be bonded to one or more other wafers and singulated to form a 3-D module.
1. A fabrication process for an electrical device comprising:
forming a hole at least partially through a first substance forming part of the electrical device, the first substance having a first surface through which the hole is formed;
depositing a conductive ink over the first surface, the conductive ink comprising electrically conductive particles dispersed in a liquid;
providing a force greater than gravity to transport the ink into the hole;
heating the ink in the hole to evaporate the liquid and cause the conductive particles to form a conductive path in the via, resulting in a conductive via; and
substantially removing any remaining ink from the first surface of the first substance.
2. The process of claim 1 wherein the step of substantially removing any remaining ink occurs after the step of heating the ink.
3. The process of claim 1 wherein the step of substantially removing any remaining ink occurs before the step of heating the ink.
4. The process of claim 1 wherein the first substance comprises a semiconductor.
5. The process of claim 1 wherein the first substance is a semiconductor wafer.
6. The process of claim 1 further comprising forming a wall on the first substance prior to depositing the conductive ink to contain the conductive ink over the first substance.
7. The process of claim 1 wherein the step of providing the force to transport the ink into the hole comprises providing a centrifugal force.
8. The process of claim 1 wherein the step of providing the force to transport the ink into the hole comprises providing a vacuum force.
9. The process of claim 8 further comprising positioning a filter between the first substance and a vacuum to substantially prevent the conductive particles from exiting the hole.
10. The process of claim 1 wherein the step of providing the force to transport the ink into the hole comprises providing an electric force.
11. The process of claim 1 wherein the step of providing the force to transport the ink into the hole comprises providing a magnetic force.
12. The process of claim 1 wherein the conductive particles are metal particles and the step of heating comprises sintering the metal particles.
13. The process of claim 1 further comprising depositing a photoresist layer on the first surface prior to depositing the ink.
14. The process of claim 13 wherein the step of substantially removing any remaining ink from the first surface of the first substance comprises removing the photoresist layer, which also removes any of the conductive particles overlying the photoresist layer.
15. The process of claim 14 wherein the photoresist layer is removed prior to heating the ink.
16. The process of claim 14 wherein the photoresist layer is removed after heating the ink.
17. The process of claim 1 wherein the step of forming the hole at least partially through the first substance comprises forming a first hole through a portion of a back side of the first substance and forming a second, smaller hole through the first surface of the first substrate to extend to the first hole.
18. The process of claim 1 further comprising forming a plurality of holes in the first substance and at least partially filling each of the holes with the conductive ink prior to the step of heating.
19. The process of claim 1 further comprising connecting electrical components to opposite ends of the conductive path in the via.
20. The process of claim 1 wherein the hole is less than 10 microns in diameter.