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Keywords
Printed circuit boards, Assembly
Abstract
The industry standard for applying the identification nomenclature to Printed Circuit Boards (PCBs) is silkscreen legend printing, using white ink. This multi-step process has minimal flexibility for applying unique legends e.g. serialization numbers to individual boards. This paper describes a new, alternative single step direct legend printing system which uses piezoelectric inkjet technology, the leading digital imaging method for a variety of industrial applications. The advantages that this, inherently clean and efficient, drop-on-demand, printing process brings to legend printing include increased flexibility, shorter process times, good legend definition, accurate placement, small footprint equipment and reduced labour and material usage.
Introduction
The manufacture of printed circuit boards (PCBs) requires a complex multi-step process. One of the final stages of the process is the component identification (ident) lettering, which is called legend (or sometimes nomenclature) printing. The main driving forces for technological advances are cost and performance, and ongoing research and development has led to the production of more sophisticated (multi-layer) and efficient (better defined circuits and components) PCBs. The technique for legend printing, however, has hardly changed since the first production of PCBs. The silkscreen method, which is used almost exclusively for PCB legend printing, is the same technique that is employed to apply lettering to t-shirts.
Since its introduction in the mid-1970's (Zoltan, 1974), drop-on-demand inkjet printing has become the most widely used method for applying ink to paper. From small desktop printers attached to personal computers to large area poster production systems, great improvements have been made in the drive electronics, head design and ink formulations of inkjet printers. Inkjet technology is now rapidly emerging as a leading digital imaging method for a variety of industrial applications other than ink on paper. Applications include 3-D graphic art, packaging, electronic and photonic device fabrication (Speakman et al., 2001; Rozenberg et al., 2001; Baron et al., 2000) and medical diagnostics and procedures.
The adaptation of drop-on-demand inkjet printing technology to legend printing of PCB panels systems has only become a viable alternative to silkscreen printing with the advent of jettable UV-curing inks compatible with improved piezoelectric printhead designs (Bearer and Kretschmer, 1997). Jetmask Ltd. has applied the technology to develop a single-step legend printer for PCBs. This paper...