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Karl's Tech Talk
By Karl Dietz
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Karl's Tech Talk: Digital Imaging Update
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 include the fact that technology had a slow, long incubation time that eventually led to accelerated 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 interconnects in acceptable yields.
It is worth mentioning that digital imaging is a more appropriate term to refer to this technology than laser direct imaging (LDI) because LDI is just one example of digital imaging, albeit 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 extra cost (e.g., with added date and lot number information). Maybe the biggest advantage is the ability to scale (i.e., to change the dimension of each individual exposure for best fit to reference points on an underlying pattern of a multilayer structure). However, early digital imaging 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 synonymous with digital imaging. While most early, commercially successful digital processes involved the use of lasers, other more recent processes use non-laser light sources such as LEDs (light emitting diodes) that consume less power, last longer, and have higher light intensity output. Alternatively, various types of mercury lamps are employed, with more than one wavelength used for imaging. Others use inkjet technology to build digitally imaged patterns such as legend print, soldermask or etch resist.
Editor's Note: This article originally appeared in the July 2016 issue of The PCB Magazine.
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