Multilayer flex circuit with non-plated outer metal layer

1. A multilayer flex circuit, comprising:

a first dual flex circuit and a second dual flex circuit, each individually comprising:

an outermost layer that is an outer metal layer;

an inner metal layer;

a plurality of blind vias or blind via holes that are open on an inner end and closed on an outer end for receiving a quantity of adhesive for coupling the first dual flex circuit to the second dual flex circuit and

a base insulation layer disposed between the outer metal layer and the inner metal layer, wherein:

for the first dual flex circuit, the outer metal layer is a non-plated metal layer that excludes any thickness of plating material on the outer surface; and

the inner metal layer of the first dual flex circuit is configured to face toward the inner metal layer of the second dual flex circuit;

a coupling layer comprising:

an adhesive that is received into inward facing openings of the blind via holes for adhesively coupling the first dual flex circuit to the second dual flex circuit; and

an electrically conductive material that electrically connects the inner metal layer of the second dual flex circuit to the inner metal layer of the first dual flex circuit.

2. The multilayer flex circuit of claim 1 , wherein the non-plated outer metal layer of the first dual flex circuit comprises fine-pitch interconnects.

3. The multilayer flex circuit of claim 1 , wherein the non-plated outer metal layer of the first dual flex circuit comprises one or more hole-free outer pad surfaces configured to electrically connect to the second dual flex circuit through the coupling layer.

4. The multilayer flex circuit of claim 3 , wherein the one or more hole-free surfaces of the first dual flex circuit are further configured to directly electrically connect to corresponding solder bumps of a high bump density component using bump on via (“BoV”) connections.

5. The multilayer flex circuit of claim 4 , wherein the one or more hole-free surfaces on which the bump on via connections are made are vertically aligned with corresponding blind vias that, after adhesively coupling of the first and second dual flex circuits, serve as buried vias that extend from the inner metal layer through the base insulation layer to the inner surface of the hole-free surfaces.

6. The multilayer flex circuit of claim 5 , wherein the coupling layer comprises an electrically conductive material that is disposed substantially in parallel to the inner metal layer of the first dual flex circuit and to the inner metal layer of the second dual flex circuit.

7. The multilayer flex circuit of claim 5 , further comprising one or more inner bumps that extend from the electrically conductive material of the coupling layer at least partially into the inward facing openings of the one or more buried vias.

8. The multilayer flex circuit of claim 2 , wherein:

the coupling layer comprises a non-conductive adhesive; and

the inner metal layer of the first dual flex circuit is electrically connected to the inner metal layer of the second dual flex circuit by electrically conductive material that extends through the non-conductive adhesive of the coupling layer.

9. The multilayer flex circuit of claim 8 , further comprising one or more blind vias that electrically connect the outer metal layer and the inner metal layer of the second dual flex circuit to the inner metal layer of the first dual flex circuit.

10. The multilayer flex circuit of claim 8 , further comprising:

a through-hole via that electrically connects the outer metal layer of the second dual flex circuit to the inner metal layer of the second dual flex circuit; and

a blind via that extends from the through-hole via and electrically connects the inner metal layer of the second dual flex circuit to the inner metal layer of the first dual flex circuit.

11. The multilayer flex circuit of claim 1 , wherein the electrically conductive material adhesively couples the first dual flex circuit to the second dual flex circuit.

12. The multilayer flex circuit of claim 1 , wherein the first dual flex circuit and the second dual flex circuit individually further comprise an inner insulation layer coupled to the inner metal layer.

13. The multilayer flex circuit of claim 1 , wherein the electrically conductive material comprises one or more of an aluminum sheet, an anisotropic conductive film, and a conductive adhesive.

14. The multilayer flex circuit of claim 1 , wherein the outer metal layer and the inner metal layer of the first dual flex circuit and the second dual flex circuit comprise one or more of copper, nickel, and silver.

15. The multilayer flex circuit of claim 1 , wherein the base insulation layer of the first dual flex circuit and the second dual flex circuit comprises one or more of polyimide, polyether ether ketone, polyester, polyethylene terephthalate, and flexible silicon.

16. A method comprising:

providing a first dual flex circuit and a second dual flex circuit individually comprising:

an outer metal layer, wherein the outer metal layer of the first dual flex circuit is a non-plated metal layer which excludes any thickness of plating material on the outer surface;

an inner metal layer for connecting to another dual flex circuit;

a plurality of blind vias or blind via holes that are open at an inner end and closed at an outer end for receiving a quantity of adhesive for coupling the first dual flex circuit to the second dual flex circuit; and

a base insulation layer disposed between the outer metal layer and the inner metal layer,

configuring the inner metal layer of the first dual flex circuit to face toward the inner metal layer of the second dual flex circuit;

adhesively coupling the first dual flex circuit to the second dual flex circuit by filling inward facing openings of the blind vias or blind via holes; and

establishing an electrical connection between the inner metal layer of the second dual flex circuit and the inner metal layer of the first dual flex circuit.

17. The method of claim 16 , wherein the step of establishing the electrical connection comprises adhesively coupling the inner metal layer of the first dual flex circuit to the inner metal layer of the second dual flex circuit using an electronically conductive material.

18. The method of claim 16 , wherein the step of establishing the electrical connection comprises creating a plated blind via that connects the outer metal layer and the inner metal layer of the second dual flex circuit to the inner metal layer of the first dual flex circuit.

19. The method of claim 16 , wherein the step of establishing the electrical connection comprises:

creating a through-hole via that connects the outer metal layer and the inner metal layer of the second dual flex circuit; and

creating a blind via that connects the inner metal layer of the second dual flex circuit to the inner metal layer of the first dual flex circuit.

20. A storage device comprising:

a multilayer flex circuit that comprises a first dual flex circuit and a second dual flex circuit, the first dual flex circuit and the second dual flex circuit individually comprising:

an outer metal layer, wherein the outer metal layer of the first dual flex circuit is a non-plated metal layer which excludes any thickness of plating material on the outer surface;

a base insulation layer;

an inner metal layer; and

a plurality of via holes that are open on an inner end and closed on an outer end for receiving a quantity of adhesive for coupling the first dual flex circuit to the second dual flex circuit;

wherein the base insulation layer is disposed between the outer metal layer and the inner metal layer, and

wherein the inner metal layer of the first dual flex circuit is configured to face toward the inner metal layer of the second dual flex circuit;

a coupling layer comprising:

an adhesive that is received into inward facing openings of the via holes for adhesively coupling the first dual flex circuit to the second dual flex circuit; and;

an electrically conductive material that electrically connects the inner metal layers of the second dual flex circuit to the inner metal layer of the first dual flex circuit.