Julian P. Partridge

Repair of circuits by laser seeding and constriction induced plating

A method of repairing circuit opens on printed circuit boards which is particularly suitable for low-melting-point substrates with small linewidth is proposed. 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 construction-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 polytetrafluoroethylene, polyimide, and glass-epoxy and has been found suitable for linewidths as small as 25 mu m. >

Effects of Electronics Assembly Processes on Benzotriazoletreated Printed Wiring Board Copper Surfaces.

The performance and reliability of personal computers, workstations and other electronic products depend on the effective soldering of electronic components to printed wiring oards (PWBs). The copper surfaces of PWBs are frequently treated with benzotriazole (or similar organic complexes) to preserve solderability by preventing copper oxide formation. However, new assembly process techniques and more complex processes may degrade protective organo-copper surface complexes and allow copper oxidation to occur, thus inhibiting subsequent solder operations. This study uses Auger electron spectroscopy (AES) in conjunction with meniscograph wettability results to determine the effects of processing conditions on the solderability of PWB surfaces. Effects are characterized for aging up to 19 months; Infrared (IR) reflow in air and nitrogen; cleaning; and temperature cycles associated with adhesive or encapsulant cure. Surface compositions, oxide thicknesses, and solderability measurements are correlated to the above process steps. For example, IR reflow in air increases oxide thickness from ∼10 A to ∼150A (relative to sputtering rates in Ta 2 O 5 with an attendant increase in the meniscograph time-to-neutral-buoyancy from 10 seconds, relative to unprocessed PWBs. Such fundamental information serves as an invaluable complement to standard phenomenological observations of defective solder joints, and can aid in guiding processing decisions for improved yield and reliability.