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86 The PCB Magazine • July 2016 Through the years, I have repeatedly covered and updated digital imaging in this column, from as far back as 1997 in CircuiTree, through a column in this magazine in November 2015. Several reasons for this extended coverage in- clude the fact that technology had a slow, long incubation time that eventually led to acceler- ated improvements and acceptance for mass production. It might also be argued that, next to the development of microvia technologies, digital imaging is probably the most innovative technology to achieve high-density intercon- nects in acceptable yields. It is worth mentioning that digital imaging is a more appropriate term to refer to this tech- nology than laser direct imaging (LDI) because LDI is just one example of digital imaging, al- beit its pioneering version. The advantages of digital circuitization techniques have been described in detail by suppliers of equipment and photoresist. Since phototool generation and conditioning are omitted, there is the advantage of shorter lead time. Small lots can be customized at no ex- tra cost (e.g., with added date and lot number information). Maybe the biggest advantage is the ability to scale (i.e., to change the dimen- sion of each individual exposure for best fit to reference points on an underlying pattern of a multilayer structure). However, early digital im- aging systems had substantial drawbacks, such as Orbotech's DP100 which used an argon ion laser with limited radiation power, high power usage, and high cooling requirements. For years, laser direct imaging (LDI) was syn- onymous with digital imaging. While most ear- ly, commercially successful digital processes in- volved the use of lasers, other more recent pro- cesses use non-laser light sources such as LEDs (light emitting diodes) that consume less pow- er, last longer, and have higher light intensity output. Alternatively, various types of mercury lamps are employed, with more than one wave- length used for imaging. Others use inkjet tech- nology to build digitally imaged patterns such as legend print, soldermask or etch resist. They by Karl Dietz KARL DIETZ CONSULTING Digital Imaging Update KARL'S TECH TALK

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