Repair of Circuits by Laser Seeding and Constriction Induced Plating

Abstract

A new and simple method of repairing circuit opens on printed circuit boards is described which is particularly suitable for low melting point substrates with small linewidths. The two-step repair process involves depositing a solid film organometallic over the open defect and forming a metallic layer by localized laser pyrolysis. After cleaning, the part is immersed in acid copper electrolyte and an increasing alternating current passed through the defective line. As a consequence of the constriction induced temperature rise, copper deposition occurs at the defect which restores the electrical and mechanical integrity of defective copper circuitry. Factors determining the selection of suitable precursors are discussed and three potential compounds for laser seeding are evaluated. The process has been demonstrated on low melting point dielectrics such as polytetraflouroethylene, polyimide, and glass-epoxy and has been found suitable for linewidths as small as 25 µm. © 1992 IEEE