US patents for laser memory repair are invalid, the US Court of Appeals for the Federal Circuit has ruled.

In 1998, EMI Group North America Inc. sued Cypress Semiconductor Corp. alleging that Cypress' processes infringed US Patent Nos. 4,826,785 and 4,935,801.

The patents relate to the use of lasers to destroy unneeded portions of interconnections between sections on a semiconductor chip. Both patents claimed that the laser's heat caused an explosion to accomplish the goal.

During a 1999 trial, an expert witness for Cypress said the described process does not cause any explosion, so Cypress' products cannot infringe the patents. A jury agreed, a district judge upheld that decision, and, in September, the appeals court affirmed it, calling the patent claims "invalid due to impossibility."