Methods of forming printed circuit boards having embedded thick film capacitors
A method of forming printed wiring boards having embedded thick-film capacitors includes covering capacitor layers with a protective coating prior to etching to prevent etching solutions from contacting with and damaging the capacitor layers and forming vias directly between the capacitor electrodes and the board circuitry.
1. A method of making a printed circuit board having outer circuitry, comprising:
providing a metallic foil;
forming a dielectric over the metallic foil;
forming a first electrode over the dielectric;
laminating a non-component side of the metallic foil to at least one dielectric material;
forming a protective coating over at least a part of the dielectric;
etching the metallic foil to form a second electrode, wherein the first electrode,
the dielectric and the second electrode form a capacitor;
forming one or more vias,
wherein the vias connect either the first electrode or the second electrode directly to the outer circuitry, and
laminating a component side of the metallic foil to at least one additional dielectric material.
2. The method of claim 1 , wherein the entire dielectric is covered by the protective coating.
3. The method of claim 2 , wherein the second electrode is at least partially covered by the protective coating.
4. The method of claim 1 , wherein the dielectric is a two-layer dielectric, the method comprising:
forming a third electrode over the two-layer dielectric, wherein the third electrode is electrically coupled to the second electrode.
5. The method of claim 1 , further comprising laminating a component side of the metallic foil to at least one additional dielectric material.
6. The method of claim 5 , wherein laminating to at least one additional dielectric material comprises:
laminating said additional dielectric material to a component side of the metallic foil after etching the metallic foil.
7. The method of claim 5 , wherein the at least one additional dielectric material is laminated over the protective coating.
8. The method of claim 1 , wherein the protective coating is a photoresist, the method comprising:
removing the photoresist after etching the metallic foil.
9. The method of claim 1 , wherein forming a protective coating comprises:
forming an organic encapsulant material over the dielectric; and
curing the organic encapsulant material.
10. The method of claim 1 , wherein forming a protective coating comprises:
forming a layer comprising glass over the dielectric; and
firing the glass layer.