Materials system for low cost, non wire-wound, miniature, multilayer magnetic circuit components
View Patent ↗This invention describes materials system and processing conditions for manufacturing magnetic circuit components such as induction coils and transformers that are non wire-wound, miniature in size and, have a low manufacturing cost. The materials system of this invention is comprised of: (1) Low Temperature Cofire Ceramic (LTCC) tapes or thick film pastes of ferromagnetic ceramics with a 20 to 750 range of magnetic permeability to form the magnetic core of the components, (2) Thick film buried silver conductor paste to form the planar induction coils on individual magnetic layers, (3) Thick film via-fill silver conductor paste to interconnect two or more of the planar induction coils through the thickness of the magnetic layers, (4) Thick film silver solderable top layer conductor paste compatible with the ferrite and, (5) Thick film dielectric paste with low magnetic permeability to redirect the magnetic flux for enhancing the magnetic coupling coefficient and to insulate the silver conductors for enhancing the dielectric breakdown voltage. The key characteristics of the materials system of this invention that facilitate manufacture of low cost non wire-wound, miniature magnetic circuit components are: (1) Mutual compatibility essential for either of the techniques, the cofire technique or the sequential technique, used for manufacturing multilayer hybrid microelectronic components, (2) Complementary thermo-physical properties such as shrinkage and thermal expansion coefficient essential for manufacturing flat multilayer magnetic components, (3) Magnetic components with magnetic coupling coefficients greater than 0.95 under optimal processing conditions and, (4) Magnetic components with dielectric breakdown voltage greater than 500V/mil under optimal processing conditions.
1. A materials system for manufacturing multilayer magnetic components comprising:
(a) a magnetically permeable ferrite material selected from the group consisting of Low Temperature Cofire Ceramic (LTCC) ferrite tape and thick film ferrite paste,
(b) metal conductor paste, wherein said metal conductor paste is disposed to be in contact with said ferrite material, and
(c) thick film dielectric paste, wherein said film dielectric paste is disposed to be in contact with and cover said metal conductor, and wherein said ferrite material has a flux containing approximately 0.2-5 weight % Bi 2 O 3 , and further wherein said metal conductor paste comprises a metal selected from the group consisting of silver, gold, copper, palladium, platinum and alloys thereof.
2. The material system of claim 1 wherein said metal conductor paste comprises:
a. a thick film buried silver conductor paste,
b. a thick film via-fill silver conductor paste and
c. a thick film solderable top layer silver conductor paste.
3. The material system of claim 2 wherein said thick film buried silver conductor paste has solids composition comprised by weight % of 93 to 100% silver, 0 to 3% grain growth inhibitor and 0 to 4% of a glass or binder.
4. The material system of claim 2 wherein said thick film via-fill silver conductor paste has solids composition comprised by weight % of 94 to 100% silver and 0 to 6% binder.
5. The material system of claim 2 wherein said thick film solderable top layer silver conductor paste has solids composition comprised by weight % of 81 to 97% silver, 2 to 7% platinum and, 1 to 12% binder.
6. The material system of claim 1 wherein said ferrite has solids composition in percent by weight comprising 84.8 to 98.8% Ni—Cu—Zn ferrite, 0.2 to 5% Bi 2 O 3 , 0 to 5% PbO, 0 to 15% filler and 0 to 10% glass binder.
7. The material system of claim 6 wherein said ferrite comprises by weight % approximately 5 to 10% Ni, 1 to 5% Cu, 10 to 20% Zn, and 0.1 to 5% PbO.
8. The material system of claim 1 wherein said ferrite comprises approximately 1 to 5 weight % Bi 2 O 3 .
9. The material system of claim 8 wherein said ferrite comprises approximately 1.25 to 3 weight % Bi 2 O 3 .
10. The material system of claim 1 wherein said thick film dielectric paste has solids composition comprised by weight % of 35 to 65% borosilicate glass and 35 to 6% filler.
11. The material system of claim 10 wherein said borosilicate glass has thermal expansion coefficient in the range of 8 to 11 ppm/° C. and softening point less than 700° C.
12. The material system of claim 1 which further comprises a grain growth inhibitor.
13. The material system of claim 1 wherein the thickness of said dielectric paste is between 20 and 70 microns.
14. The material system of claim 1 wherein said magnetic components have magnetic coupling coefficient greater than 0.95 and dielectric breakdown voltage greater than 500V/mil between elements.
15. The material system of claim 1 further comprising at least one registration hole formed in said ferrite material.
16. The material system of claim 1 further comprising at least one via hole formed in said ferrite material.
17. The material system of claim 16 wherein the at least one via hole is operable to provide for an electrical interconnect.