Electronic package with filled blinds 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. For use in a circuit assembly, a stacked sub-assembly comprising:
a) a conductive metal plane selected from the group consisting of a ground plane and a power plane and comprising a conductive metal core;
b) a first dielectric layer having a first surface laminated to said core;
c) a first landless blind via extending through the dielectric layer to a surface of the core, said via completely filled with a conductive metal from the core, said conductive metal in electrical contact with the core, and
d) a second dielectric layer laminated to the first dielectric layer and including a second blind via aligned with the first blind via and having a base in contact with the first blind via.
2. The stacked sub-assembly according to claim 1 wherein the first blind via is larger in cross section than said base of the second via.
3. The stacked sub-assembly according to claim 1 wherein the first blind via includes a contact pad on a second surface of the first dielectric layer, the second dielectric layer is laminated to said second surface of the first dielectric layer, and the second layer blind via is aligned with the first blind via and has a base in contact with the contact pad.
4. The stacked sub-assembly according to claim 3 wherein the first blind via is smaller in diameter than said base of the second layer via, and the contact pad is larger than said base.
5. The stacked sub-assembly according to claim 1 wherein the metal in the first blind via is copper that has a nearly equiaxial fine grained structure and mechanical properties including an elongation between about 10% and about 20% and an ultimate tensile strength of between about 30,000 psi and about 50,000 psi.
6. The stacked sub-assembly according to claim 1 wherein the deposited metal is selected from the group consisting of copper, nickel, gold, palladium and alloys thereof.
7. An electronic sub-assembly comprising a conductive metal plane selected from the group consisting of a ground plane and a power plane and comprising a conductive metal core laminated to a first dielectric layer containing a first blind via, and a second dielectric layer contiguous to the first dielectric layer, and containing a second blind via stacked on the first blind via, The second blind via including a base in contact with the first blind via, wherein the first blind via is larger in cross section than said base of the second layer via, wherein electrical continuity is established from the second layer via through the first via to the core, the sub-assembly made according to the method of:
a) preparing a contaminant-free hole in the first dielectric layer terminating at the surface of the core;
b) depositing copper in the prepared hole solely on and building up from the surface of the metal core without depositing on the wall of the hole to form a completely filled landless blind via contacting the base of the second layer via, said copper having a nearly equiaxial fine grained structure and mechanical properties including an elongation between about 10% and about 20% and an ultimate tensile strength of between about 30,000 psi and about 50,000 psi; and
c) laminating the second dielectric layer to the first dielectric layer, whereby the second layer via is aligned with the first blind via.
8. The sub-assembly according to claim 7 wherein a contact pad is deposited on the second surface of the first dielectric layer and covers the first blind via, the second layer via is aligned with the first blind via and has a base in contact with the contact pad, the first blind via being smaller in cross section than said base of the second layer via, and the contact pad being larger than said base.
9. The sub-assembly according to claim 7 wherein the core is a conductive layer that is made a cathode in an acid copper electroplating bath, and copper is electroplated into the hole to plate solely from the core to form the filled blind via.