The Foxboro Company

Paul E Grandmont

Harold Lake

Richard A Anderson

A microporous, photoprocessable, moderately hydrophilic material on which metal can be deposited directly using electroless plating techniques, and its use in preparing printed wiring boards and circuit components.

Multilayer circuit board having microporous layers and method for making

Multilayer circuit board having microporous layers and process for

A CAD driven photoplotter selectively exposes a photographic imaging layer without affecting the underlying UV sensitive resist on a substrate to make a printed wiring board, for example. The image layer is developed on the board and used as an in situ mask for the underlying UV resist during exposure to UV. After UV exposure, the image layer is peeled off to allow conventional processing of the resist. The in situ mask is preferably applied in the form of a baseless, high contrast, high gamma emulsion layer bonded to the protective cover sheet over the uncured resist. To facilitate application, the emulsion layer is carried by a release paper which is removed before photoplotting. After UV exposure, the cover sheet and emulsion layer are integrally peeled from the resist.

Method of patterning resist

A process for making additive multilayer circuit boards uses separately designed and fabricated composite structures each consisting of a patterned conductive metal foil supported by a photo-processible insulating film. The composite is bonded foil pattern side down to the substrate or pre-existing multilayer structure and selected areas of the insulating film are removed down to underlying metal sites for electroless plating. All of the apertures in the insulating film are then electrolessly plated full of metal flush to the upper surface. Additional patterned composites are applied and plated up as desired to create blind vias and new conductor patterns layer by layer. In an alternate process a foil clad composite is bonded to an existing substrate foil side up. The insulating layer is selectively etched through windows photoetched in the foil layer. The voids in the insulator layer expose copper sites on the underlying composite. The voids are plated full of metal to form vias and the foil layer is photoetched to make a conductor pattern. The process is repeated to make a multilayer PWB.

Multilayer circuit board fabrication process

A method for patterning a photoresist or insulating layer on a printed wiring board utilizes two photoreactive coatings comprising a photoprocessable ultraviolet (UV) sensitive layer overlaid with a thin, unexposed, undeveloped strip base silver film. A white light x-y plotter, preferably employing an octagonal aperture, is driven directly from a CAD system to expose the film on the board in the desired pattern without affecting the underlying UV sensitive layer. The film is then developed on the board and employed as an in situ mask for the underlying UV layer during exposure of the board to a UV flood lamp. After UV exposure the film is peeled off to allow conventional processing of the selectively polymerized layer. This technique produces high resolution, inspectable onboard masks in full registration using reliable low energy plotters.

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Franklin, MA, United States of America

Paul E Grandmont