We present several laser direct-write patterning technologies for use with photosensitive or non-photosensitive thick-film conductive inks. In a first case, a ultraviolet (UV) laser processing system (Electro Scientific Industries) was used to directly expose photodefinable conductive silver ink (Fodel s 6778, Dupont). After developing and further processing, the process yielded patterned traces approximately 25 mm wide. In a second case, the UV laser was used to photo-ablate the silver conductive ink to form spaces, resulting in line resolution as fine as 8 mm trace width and 12 mm space width (20 mm pitch). In another experiment, the laser was used to pattern pre-fired conductive gold ink (Heraeus KQ500) covered with photosensitive resist material. After ablation of the resist and underlying gold, the resist was removed yielding well-defined traces down to 25 mm pitch. We also ablated unfired Heraeus KQ 500 ink followed by post-firing to produce a well-defined inductor pattern. The above processes were performed both with a 25 mm Gaussian-shaped laser beam and a special shaped 10 mm ''top hat'' square beam, ideal for even laser exposure across the beam aperture. The square-beam enabled finer line resolution with the ablation process, but was not as effective for the laser exposure process in comparison to the Gaussian beam. Post firing of the Fodel s parts was performed using both a batch box furnace and an infrared belt furnace with multiple heat zones. Both firing methods yielded well-defined traces with the belt-firing process supporting slightly finer trace resolution. The laser direct-write processes enable fine-line patterning of conductors for single or multilayer ceramic circuit fabrication. Direct laser writing offers the advantage of direct patterning from a computer automated design (CAD) file without requiring a mask and exposure system and can also be used in combination with traditional screen printing or mask lithography to enhance the resolution and accuracy of thick-film patterning.
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