Low-temperature curable photosensitive compositions
View Patent ↗The invention relates to low-temperature curable photosensitive compositions containing a polyamic acid, which compositions are developable in aqueous alkaline solutions and are curable, at a temperature of at least 160° C. and up to 200° C., to low modulus polyimides suitable for use in electronic circuitry applications, and which are particularly suitable for use in flexible circuit applications where low curl, low temperature curing, and good adhesion is a significant advantage.
1. A method for preparing, then exposing and then developing a single-layer low-temperature curable photosensitive composition for flexible circuitry applications, comprising the steps of:
reacting one or more aromatic dianhydrides with one or more aliphatic diamines with a dry solvent to form a polyamic acid solution;
providing an ethylenically unsaturated photo monomer mixture, comprising a compound selected from the group consisting of: amine (meth)acrylates, amine methacrylamides, and combinations thereof; and, a non-amine-containing (meth)acrylate compound;
adding the photo monomer mixture, a photo initiator, and a sensitizer to the polyamic acid solution to form a photosensitive composition;
exposing the photosensitive composition to actinic light to form an exposed composition; and
developing the exposed composition in 1% aqueous carbonate at 80° C. for use in a flexible circuitry application.
2. The method of claim 1 further comprising the step of curing the composition to form a polyimide having a modulus of less than 2 GPa.
3. A method of making a flexible circuit comprising the steps of:
reacting one or more aromatic dianhydrides with one or more aliphatic diamines with a dry solvent to form a polyamic acid solution;
providing an ethylenically unsaturated photo monomer mixture, comprising a compound selected from the group consisting of: amine (meth)acrylates, amine methacrylamides, and combinations thereof; and, a non-amine-containing (meth)acrylate compound;
adding the photo monomer mixture, a photo initiator, and a sensitizer to the polyamic acid solution to form a photosensitive composition;
coating the photosensitive composition on a releasable support sheet to form a coated composition;
laminating the coated composition to a flexible printed circuit substrate;
exposing the photosensitive composition to actinic light to form an exposed composition; and
developing the exposed composition in 1% aqueous carbonate at 80° C.
4. The method of claim 3 further comprising the step of curing the composition to form a polyimide having a modulus of less than 2 GPa.
5. The method according to claim 4 , wherein polyimide forms an adhesive layer in an electrical circuit.
6. The method according to claim 3 wherein the laminating of the photosensitive composition to the substrate is performed using hot roll lamination with roll temperature at 50° C. with N-methyl pyrrolidone liquid assist.
7. The method according to claim 1 or claim 3 , further comprising the step of:
adding an adhesion promoter to the photosensitive composition prior to adding the photo monomer mixture.
8. The method according to claim 1 or claim 3 , further comprising the step of:
adding a dye to the photosensitive composition prior to adding the photo monomer mixture.
9. The method of claim 2 or claim 4 wherein the curing of the composition is at a temperature of at least 160° C. and up to 200° C. for about one hour.