Composite organic encapsulants
This invention relates to compositions, and the use of such compositions for protective coatings, particularly of electronic devices. The invention concerns a fired-on-foil ceramic capacitors coated with a composite encapsulant and embedded in a printed wiring board.
1. An organic two-layer encapsulant composition for coating one or more embedded formed-on-foil ceramic capacitors, said two-layer encapsulant comprising a first encapsulant layer and a second encapsulant layer wherein said first encapsulant layer comprises (a) a polyimide and said second encapsulant layer comprises (b) an epoxy-containing cyclic olefin resin, (c) a phenolic resin, (d) an epoxy catalyst; and wherein said embedded formed-on-foil ceramic capacitors comprise a capacitor element and a prepreg wherein said first encapsulant layer is in direct contact with said capacitor element and said second encapsulant layer is in direct contact with said first encapsulant layer.
2. The organic two-layer encapsulant composition of claim 1 wherein the polymide has a water absorption of 2% or less and a glass transition temperature greater than 280° C.
3. The organic two-layer encapsulant composition of claim 1 wherein the epoxy-containing cyclic a olefin resin has a water absorption of 2% or less.
4. The organic two-layer encapsulant composition of claim 1 wherein the phenolic resin has a water absorption of less than 2%; an epoxy catalyst; optionally one or more of an electrically insulated filler, a defoamer and a colorant and one or more organic solvents.
5. The organic two-layer encapsulant composition of claim 1 wherein said first encapsulant layer further comprises one or more components selected from the group comprising an electrically insulated filler, a defoamer, a colorant, an epoxy resin, and mixtures thereof.
6. The encapsulant composition of claim 1 wherein said encapsulant composition is cured to form a two-layer organic encapsulant and wherein said cured two-layer organic encapsulant provides protection to the capacitor when immersed in sulfuric acid or sodium hydroxide having concentrations of up to 30%.
7. The encapsulant composition of claim 1 wherein said encapsulant composition is cured to form a two-layer organic encapsulant and wherein the cured two-layer organic encapsulant provides protection to the capacitor in an accelerated life test of elevated temperatures, humidities and DC bias.
8. The encapsulant composition of claim 1 wherein the encapsulant composition is used to fill an etched trench that isolates the top and bottom electrodes of an embedded capacitor.
9. The encapsulant composition of claim 1 wherein said encapsulant composition is cured to form a cured organic encapsulant and wherein the water absorption is 1% or less.
10. The encapsulant composition of claim 1 wherein the composition can be cured at a temperature of less than or equal to 190° C.
11. The encapsulant composition of claim 1 wherein said encapsulant is cured to form a cured organic encapsulant and wherein the adhesion of said encapsulant to the capacitor and to the prepreg above the capacitor is greater than 2 lb force/inch.