Direct‐Write Laser Exposure of Photosensitive Conductive Inks Using Shaped‐Beam Optics

Abstract

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® 6778, Dupont). After developing and further processing, the process yielded patterned traces approximately 25 μm 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 μm trace width and 12 μm space width (20 μm 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 μm 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 μm Gaussian‐shaped laser beam and a special shaped 10 μm “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® 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.