Developing PCB Manufacturing Techniques during the First Decades
by Gene H. Weiner, Gene Weiner Associates
As a student technician at MIT Lincoln Laboratories, I tested and validated the first photoplotter during the days of hand taping patterns and photoreducing a picture taken with a large Brown Camera. We converted a Head milling machine, replacing the bit with a hypodermic needle through which we passed light from a Xenon point source. The hypodermic needle served as a collimator. Photosensitive film was vacuum-locked onto the tooling plate while the needle traversed it with the light switching on and off to make the exposure of the circuit pattern. The inventor was E.A. Guditz, Engineer.
While at Lincoln Laboratories, we also built the first HDI additive circuit as part of a PWB memory plane in 1957. We punched holes in XXXP substrate, dropped in memory cores, encapsulated with Dow's Sylguard, metallized with immersion Ag, electroplated Cu to thickness, applied photoresist (KPR by Kodak), contact printed flat surfaces, and simultaneously projection printed patterns through the holes in the ferrite cores. We etched and stripped the resist, and voila, X, Y, Drive, and inhibit circuits were formed through each core as well as the two sides of the structure. Lines and spaces were initially 10 mils through a 50 mil ID core. Later (1958) we printed 6 mil lines and spaces through a 30 mil ID core. E.A. Guditz and I demonstrated additive circuit techniques and projection printing through planar mask on WGBH-TV (educational TV) in 1957.
In 1958, a laboratory error in the cellar of Charles and Lucia Shipley's elegant home in fashionable Auburndale, Mass., turned into one of the industry's major inflection points - the development of Catlyst 6F, a colloidal solution containing Pd, which eliminated the need for sanding deposits off of panel surfaces after metallizing drilled holes in laminates. It sounded the death knell for using eyelets to connect circuitry from one side of a panel to the other. I was fortunate enough to become Shipley's first full-time employee and worked on the development and test of a wide variety of acidic, organic (albumen), and alkaline catalytic materials for patent applications on materials that would initiate electroless plating.
In 1960, I introduced the first alkaline etchant in the PWB industry (Etchant M-U [for minimal undercut] by MacDermid). At its peak it, and its descendants, became the primary industry etchant. Simple waste treatment provided a variety of marketable salts out of the dissolved copper. M-U was a laboratory curiosity named x-381. It was developed to remove copper from heat treated steel typewriter balls for NCR, but had never been commercialized. I asked if it could be used to etch Cu from Cu-clad PWB laminated and was told "NO!" I tested it in a 3.5 gallon Chemcut etching machine in a laboratory hood. It worked and the alkaline nature (ammonia based with a pH of about 9.8 +/-) eliminated pinholes and reversed the normal undercut caused by acidic etchants (ferric and chromic acids) of the period when etching gold plated boards. I set up a test at with Bert Krasnow for a warm summer Friday afternoon at Precision Circuits in New Rochelle, New York. Shortly after we began the test, we heard the sound of feet scrambling down the stairs from the offices located over the production facility. The exhaust from the etcher went to the roof. It was located next to the roof-top air conditioning units, picked up the ammonia and blew it into the office causing the most rapid and complete evacuation in company history. Later, in 1961, Metex Etcant M-U was named product of the year at one of the first major NEPCON shows held at the Coliseum.
In the mid-60's, as VP of marketing and sales for Dynachem, I introduced the world's first totally aqueous developing dry film photo resist, from the now extinct company. The product was one that was developed to a planned goal by Mike Gilano and Irv Martinson, Dynachem founders, and Dr. Mel Lipson.