Parlex Corporation

Arthur J Demaso

Darryl J McKenney

Craig S Wilson

Kathy A Gosselin

A process for providing bond enhancement and an etch resist for a printed circuit board is provided. A sheet comprising at least a layer of copper is immerses in a first immersion tin solution comprising a tin metal and a complexing agent in an acidic medium for a time sufficient to deposit a first heavy tin deposit on the sheet. The sheet is then immersed in a second immersion tin solution comprising stannous tin ions and stannic tin ions and a complexing agent in an acidic medium for a time sufficient to deposit a second thin tin deposit on the sheet. The second thin tin deposit has a thickness less than a thickness of the first heavy tin deposit. A rough surface texture providing mechanical adhesion sites results. The board is then treated with a coupling agent, such as silane, for enhanced bonding to a subsequent epoxy or other polymer prepreg. Additionally, the first heavy tin deposit may serve as an etch resist in subsequent fabrication of the provided circuit board.

Process for providing bond enhancement and an etch resist in the fabrication of printed circuit boards

In a rigid/flex circuit board and fabricating process, patterns of electrical traces are formed by etching conductive layers on outer surfaces of a flexible multi-layer circuit structure. A protective barrier material is deposited on the etched traces using an 'electroless' process, such as immersion of the flexible circuit board in an aqueous solution containing ionic tin. The protective barrier material adheres to and encapsulates the copper traces. An outer circuit structure including a bondfilm of epoxy-impregnated fiberglass ('prepreg' bondfilm) and a copper foil layer is laminated onto the flexible circuit structure. The prepreg bondfilm has a window area removed by routing or an equivalent process prior to being laminated to the flexible structure. The window area defines a flex area of the rigid/flex circuit board that will be relatively flexible. The portion of the outer copper foil above the window area of the prepreg bondfilm is then removed using a chemical etchant to which the previously-applied protective barrier material is immune, such as an ammoniacal etching solution. After the copper foil is etched, the protective barrier material in the flex area of the flexible circuit is stripped away. A flexible sealing coating is then applied to the circuit board to cover the edges of the outer laminated circuit structure.

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Nashua, NH, United States of America

Arthur J Demaso