Method of forming multilayer capacitors in a printed circuit substrate
View Patent ↗Methods of forming embedded, multilayer capacitors in printed circuit boards wherein copper or other electrically conductive channels are formed on a dielectric substrate. The channels may be preformed using etching or deposition techniques. A photoimageable dielectric is an upper surface of the laminate. Exposing and etching the photoimageable dielectric exposes the space between the copper traces. These spaces are then filled with a capacitor material. Finally, copper is either laminated or deposited atop the structure. This upper copper layer is then etched to provide electrical interconnections to the capacitor elements. Traces may be formed to a height to meet a plane defining the upper surface of the dielectric substrate or thin traces may be formed on the remaining dielectric surface and a secondary copper plating process is utilized to raise the height of the traces.
1. A method of forming a multilayer capacitor within a laminated circuit packaging structure, the method comprising:
a) providing an assembly comprising a dielectric substrate having parallel traces of electrically conductive material formed on a major surface thereof and a layer of photoimageable dielectric laminated to said major surface, covering said major surface and said parallel traces of electrically conductive material;
b) exposing and etching said photoimageable dielectric above said parallel traces of electrically conductive material to reveal said parallel traces of electrically conductive material through openings in said photoimageable dielectric defined by individual traces of electrically conductive material;
c) plating copper onto said revealed parallel traces of electrically conductive material, filling said openings to a thickness that is coplanar with a top surface of a remaining portion of said layer of photoimageable dielectric;
d) exposing and etching said photoimageable dielectric a second time between said copper-plated parallel traces of electrically conductive material to create openings defined by adjacent copper-plated parallel traces of electrically conductive material; and
e) dispensing a capacitor-forming material into said openings defined by adjacent copper-plated parallel traces of electrically conductive material, filling said openings to form a vertically-oriented multilayer capacitor, the capacitance thereof being proportional to the thickness of said photoimageable dielectric.
2. The method of forming a multilayer capacitor within a laminated circuit packaging structure as recited in claim 1 , the method further comprising:
f) curing said capacitor-forming material after step e).
3. The method of forming a multilayer capacitor within a laminated circuit packaging structure as recited in claim 1 , the method further comprising:
f) laminating a planar copper sheet over the resulting capacitor of step e), such that the planar copper sheet is in electrical contact with said copper-plated parallel traces of electrically conductive material; or depositing a copper layer over the resulting capacitor of step e), such that the copper layer is in electrical contact with said copper-plated parallel traces of electrically conductive material.
4. The method of forming a multilayer capacitor within a laminated circuit packaging structure as recited in claim 3 , the method further comprising:
g) after step f), etching said planar copper sheet or said copper layer to provide a pattern of electrically conductive traces.