Photoimaging development

Cinnamates occupy an important place in the history of photochemistry. Schmidt and his co-workers [18] used the solid state photochemistry of cinnamic acid and its derivatives to develop the idea of topochemical control of photochemistry in the crystalline state. Minsk [19] developed poly(vinyl cinnamate) as the first polymer for photoimaging. The cinnamate chromophore is still commonly incorporated in photopolymers of all types, including LC polymers, to enable them to be photochemically cross-linked [20], and a number of reports of the photochemistry of such MCLC and SCLC polymers are summarized below. 

Photoresist A photoimaging material, generally applied as a thin film, whose local solubility properties can be altered photochemically. A subsequent development step produces an image which is useful for the fabrication of microelectronic devices (e.g., integrated circuits). 

Timpe classified the onium salts as bivalent initiators , that is, capable of initiating both radical and cationic cures simultaneously, hence capable of so-called dual cures of mixtures of radical and cationically polymerizable monomers [18]. This theme has been developed in the more recent review by Rabek [19]. More recently, use of photogenerated Bronsted or Lewis acids to effect decomposition of acid-labile polymers has found utility in photoimaging and been reviewed [20],... 

Photoinitiated cationic polymerizations have numerous applications involving photoimaging. Epoxy-based photoresists with high resolution derived from commercially available resins have been developed (22) and the use of these same materials in plastic flexographic printing plates has been shown in our laboratory. 

Miyoshi, K. Suwa, A. Tomikawa, M. Alkali-developable photoimaging polyimide compositions for coatings or interlayer insulators of electronic devices. Jpn. Kokai Tokkyo Kobo JP 2003005369, 2003 Chem. Abstr. 2003,138, 98183. 

To obtain finer lines and smaller vias, one can use photoimageable thick-film process for dielectric and conductors and diffusion patterning. The photoimageable thick-film process involves the use of a photoactive paste printed on a substrate and exposed through artwork or a mask to define circuif characteristics, lines, and vias. The materials are developed in an aqueous process and then fired using the conventional thick-film fechnique. Copper, silver, and gold metallizations are used, and layer coxmts of up to 10 circuit layers are possible. 

Coating of the bare copper prodnct with either dry film or hquid photoimageable solder mask, exposing of the panel with the PCB cnstomer-snpplied artwork pattern, developing of the pattern (exposing the sites requiring solder), and curing of the solder mask... 

Photoimageable Discrete. In a photoimageable discrete process, resistive compositions have been dispersed in traditional solder mask-like materials, which are applied to the surface of an etched layer. Imaging and development leave the desired geometry resistor after the development step. 

Normally, embedded formed polymer capacitors are made from purchased sheet materials. It is difficult for the board fabricator to apply a liquid dielectric formulation precisely to laminate, but one photolithographic capacitor formation technique has been developed. Unneeded dielectric is removed with a developer solution similar to hquid photoimageable solder mask. 

Solder mask began with the use of two-part epoxy, thermally curable inks that were an offshoot of inks that were used in the printing industry. These inks were applied by screen printing with the use of a patterned screen, since these materials were not photoimageable. One-part inks that were ultraviolet (UV) curable were available soon after, but these also had to be applied by a patterned screen because they could not be imaged and developed. 

Photoimageable solder masks were developed in the mid-1970s and were offshoots of photoresist materials used for patterning the circuitry. Photoimageable solder masks were developed in both liquid (LPI) and dry film (DFSM) and both were used widely. Today, more than 98 percent of the solder mask used is applied in liquid form, and most is photoimageable. 

Photoimageable solder masks may be developed in either aqueous or solvent chemistries. The developer chemistry needed depends on the mask formulation. In the development process, solder mask that has not been exposed to UV hght and pol5merized is washed away, or developed, from the PCB panel to reveal the desired pattern of solder mask. 

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