Patent attributes
The present invention is directed to phosphorus containing (or “halogen free”) multi-layer flame retardant photoimagable compositions useful as a coverlay material in a flexible electronic circuitry package. These compositions generally contain a top layer and bottom layer adjacent to one another both being photosensitive and comprising phosphorus containing acrylates and phosphorus-containing photo-initiators mixed with a polymer binder. These compositions typically have phosphorus in the top layer in an amount between, and including, any two of the following numbers 2.0, 2.2, 2.4, 2.6, 2.8, 3.0, 3.2, 3.4, 3.6, 3.8, 4.0, 4.2, 4.4, 4.6, 4.8, 5.0, 5.2, 5.4, 5.6, 5.8, 6.0, 6.2, 6.4, 6.6, 6.8, 7.0, 7.2, 7.4, 7.6, 7.8, 8.0, 8.2, 8.4, 8.6, 8.8, 9.0, 9.2, 9.4, 9.6, 9.8, and 10.0 weight percent, and have phosphorus in the bottom layer in an amount between, and including, any two of the following numbers, 0.0, 0.2, 0.4, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6, 1.8, 2.0, 2.2, 2.4, 2.6, 2.8, 3.0, 3.2, 3.4, 3.6, 3.8, and 4.0 weight percent.
