Method of forming filled blind vias
View Patent ↗The density of electronic packaging and the electrical reliability of the sub-assemblies utilizing stacked blind vias are improved by providing a blind, landless via in a first dielectric layer laminated to a conductive metal core serving as a ground plane or a power plane. A hole is provided through the dielectric layer extending to the core. A metal, such as copper, is deposited electrolytically using the metal core as the cathode, or electrolessly without seeding into the hole. The metal is deposited on the core and progressively builds in the hole to the depth required for the via. A second dielectric layer is laminated to the first, and is provided with a second layer blind via aligned with the first via. This second via may be formed by conventional plating techniques. Multiple dielectric layers with stacked blind vias can be assembled in this manner.
1. A method of forming a first blind via through a first dielectric layer having a first surface laminated to a conductive metal core, said first blind via terminating at a first surface of said conductive metal core, comprising the steps of;
a) preparing a contaminant-free hole in the dielectric layer terminating at the surface of the conductive metal core, and
b) electrodepositing conductive copper metal from an acid copper bath into said hole using the conductive metal core as a cathode to build the copper deposit from the core surface, whereby the copper has a nearly equiaxial fine grained structure, an elongation between about 10% and about 20%, and an ultimate tensile strength of between about 30,000 psi and about 50,000 psi.
2. The method according to claim 1 wherein the contaminant-free hole is completely filled with the copper to form a filled blind via.
3. The method according to claim 1 further including laminating a second dielectric layer to a second surface of the first dielectric layer, providing a second layer blind via in the second dielectric layer aligned with the firs blind via, and having a base of the second layer via in contact with the first blind via.
4. The method according to claim 3 wherein the cross-sectional area of the first blind via is larger than the cross-sectional area of the base of the second layer blind via.
5. The method according to claim 3 further including the step of plating a contact pad on the second surface of the first dielectric layer in contact with the filled via.
6. The method according to claim 5 wherein the contact pad has a cross-section that is larger than the cross-section of the base of the second layer blind via.
7. The method according to claim 1 wherein excess metal extending above the dielectric surface is removed to form a landless filled blind via.
8. A method of forming first blind via through a first dielectric layer having a first surface laminated to a conductive metal core, said via terminating at a first surface of the conductive metal core, comprising the steps of:
a) preparing a contaminant-free hole in the dielectric layer terminating at the surface of the conductive metal core,
b) plating a conductive metal into the contaminant-free hole to deposit the metal solely on the surface of the conductive metal core, and to build the metal deposit from the surface of the conductive metal core completely filling said hole with metal to form a filled landless blind via having an exposed surface, and
c) imparting a rough surface to the top of the filled landless via.
9. The method according to claim 8 wherein the hole in the dielectric layer is prepared by laser drilling, followed by removal of residual drill debris.
10. The method according to claim 8 wherein the conductive metal is selected from the group consisting of copper, nickel, gold, palladium and their alloys.
11. The method according to claim 10 wherein the conductive metal is copper that is electroplated into the hole from an acid copper bath using the conductive metal core as a cathode.
12. The method according to claim 11 wherein the copper is electrodeposited in the contaminant-free hole to form a newly equiaxial fine grained structure.
13. The method according to claim 12 wherein the copper is deposited to form a structure having an elongation between about 10% and about 20% and an ultimate tensile strength of between about 30,000 psi and about 50,000 psi.
14. The method according to claim 8 wherein the metal is plated in the hole from an electroless plating bath without seeding.
15. The method according to claim 14 including the steps of laminating a second dielectric layer to the second surface of the first dielectric layer, and providing a second layer blind via aligned with the first blind via sand having a base in contact with the contact pad.
16. The method according to claim 15 wherein the cross-sectional area of the first blind via is larger than the cross-sectional area of the base of the second layer blind via.
17. The method according to claim 16 wherein the contact pad has a cross-section that is larger than the cross-section of the base of the second layer blind via.
18. The method according to claim 14 wherein the electroless plating bath is a copper bath.
19. The method according to claim 8 wherein the rough surface is imparted by plating palladium dendrites on the top of the filled landless via.
20. The method according to claim 8 wherein the rough surface is imparted by etching.
21. The method according to claim 8 further including the step of plating a contact pad on the second surface of the first dielectric layer in contact with the filled via.
22. The method according to claim 8 wherein excess metal extending shove the dielectric surface is removed to form a landless filled blind via.