Say your dear client fears that a patent holder can hardly wait to sue YDC for infringement. YDC — a lovely outfit with lots of nice people — asks you what to do. You knit your brows, think deep thoughts, draw on the deep well of experience, conduct thought experiments, and come up with a plan. SUE FIRST for a declaratory judgment of non-infringement, you tell YDC. And so you do.
Did you just mess up? By, for instance, making victory on the merits harder because you caused YDC to take on the main burden of a plaintiff — the burden of proof, which would normally fall on the patent holder that claims infringement?
No. You did not, in this case, do that, although YDC does in fact bear the burden of proof. But suing for a DJ didn't shift the burden. It never does. YDC has the burden in this case because of the reason it claims non-infringement. YDC claims it has a license from the patent holder to practice the invention. If the patent holder had sued for infringement, YDC would have the burden of showing that the license bars the claim. And so YDC keeps that burden when it SUES FIRST for a declaratory judgment.
Simple as pi. Medtronic Inc. v. Boston Scientific Corp., No. 11-1313 (Fed. Cir. Sept. 18, 2012).