Microcircuit package having ductile layer
A microcircuit package having a ductile layer between a copper flange and die attach. The ductile layer absorbs the stress between the flange and semiconductor device mounted on the flange, and can substantially reduce the stress applied to the semiconductor device. In addition, the package provides the combination of copper flange and polymeric dielectric with a TCE close to copper, which results in a low stress structure of improved reliability and conductivity.
1. A microcircuit package comprising:
a substrate having a first surface, said substrate formed of copper, a copper alloy, silver or a silver alloy;
a layer of ductile material having a first surface and a second surface, the first surface of the layer attached to the first surface of the substrate;
a barrier layer having a first surface and a second surface, the first surface of the barrier layer attached to the second surface of the layer of ductile material;
a gold layer having a first surface and a second surface, the first surface of the gold layer attached to the second surface of the barrier layer; and
a eutectic layer having a first surface and a second surface, the first surface of the eutectic layer attached to the second surface of the gold layer, said eutectic layer formed of a gold-tin (AuSn) alloy, a gold-silicon (AuSi) alloy or a gold-germanium (AuGe) alloy, said first surface of said eutectic layer for mounting a semiconductor die thereon.
2. The microcircuit package of claim 1 wherein the layer of ductile material is silver, copper or an alloy of silver and copper.
3. The microcircuit package of claim 2 wherein the layer of ductile material is electroplated onto the first surface of the substrate.
4. The microcircuit package of claim 2 wherein the layer of ductile material is applied to the first surface of the substrate by plating, cladding, evaporation or sputtering.
5. The microcircuit package of claim 2 wherein the layer of ductile material has a hardness of less than about 80 Knoop and a thickness of about 100-1000 micro-inches.
6. The microcircuit package of claim 5 wherein the barrier layer is nickel or nickel cobalt.
7. The microcircuit package of claim 5 wherein the eutectic layer is a solder with a eutectic temperature of about 250° C. or higher.
8. The microcircuit package of claim 5 wherein the substrate is a copper zirconium alloy.
9. The microcircuit package of claim 5 wherein the substrate has a hardness of greater than about 80 Knoop.
10. The microcircuit package of claim 5 wherein the gold layer has a thickness of about 30-50 micro-inches.
11. The microcircuit package of claim 1 which also has a dielectric material attached which has a TOE in the range of 12-25 ppm/°C.
12. The microcircuit package of claim 11 , where the dielectric material is a high temperature polymeric material that has a composition which includes a chemical group selected from the chemical groups consisting of: hydroquinone (HQ), 4,4 bisphenol (BP), bis (4-hydroxylphenyl ether) (POP), terephthalic acid (TPA), 2,6 naphthalene dicarboxylic acid (NPA), 4,4 benzoic acid (BB), 4-hydroxybenzoic acid (HBA), 6-hydroxy-2-napthoic acid (HNA).
13. The microcircuit package of claim 1 , wherein the substrate is copper or a copper alloy.
14. The microcircuit package of claim 13 , wherein the substrate has a thickness in the range of about 0.040-0.060 inches.
15. The microcircuit package of claim 1 , wherein the substrate is copper or a copper alloy having a hardness greater than about 80 Knoop.
16. The microcircuit package of claim 15 , wherein the substrate has a hardness in the range of about 85-100 Rockwell F.
17. The microcircuit package of claim 1 further including at least one semiconductor die attached to said second surface of said eutectic layer.
18. The microcircuit package of claim 5 wherein the layer of ductile material has a thickness of about 100-500 micro-inches.
19. The microcircuit package of claim 9 wherein the substrate has a hardness in the range of about 85-100 Rockwell F.
20. A microcircuit package comprising:
a substrate having a first surface, said substrate formed of copper, a copper alloy, silver or a silver alloy;
a layer of ductile material having a first surface and a second surface, the first surface of the layer attached to the first surface of the substrate;
a barrier layer having a first surface and a second surface, the first surface of the barrier layer attached to the second surface of the layer of ductile material;
a gold layer having a first surface and a second surface, the first surface of the gold layer attached to the second surface of the barrier layer; and
a eutectic layer having a first surface and a second surface, the first surface of the eutectic layer attached to the second surface of the gold layer, said eutectic layer formed of a lead free material selected from the group of a tin-silver-copper (SnAgCu) alloy, a tin-silver (SnAg) alloy, an antimony-tin (SbSn) alloy, a tin-zinc (SnZn) alloy, a tin-indium (SnIn) alloy and bismuth (Bi), said first surface of said eutectic layer for mounting a semiconductor die thereon.
21. The microcircuit package of claim 20 further including at least one semiconductor die attached to said second surface of said eutectic layer.