Cleaning laser debris from TAB circuits:

摘要

The formation of carbon residue while UV lasers drill microvias in polyimide or other dielectric materials is normal and expected. The UV lasers that drill microvias use a process called photoablative decomposition (or simply photoablation). The process employs the unique properties of high-energy UV photons to break chemical bonds of the material drilled. Sometimes this process is termed a non-thermal process because there is a minimal heat affected zone. The resulting carbon debris forms within the laser plasma plume and drops back to the surface of the material being processed. Because the carbon debris needs to be removed, the first cleaning processes used are typically solvent- or detergent-based, or in the worst case a reactive oxygen plasma cleaning technique is used. Either way, the use of chemicals or a reactive plasma process increases cost and does not always remove the carbon down to the sub-micron level, leading to potential shorts or defects at downstream plating or laminating. This article describes the use of water-soluble coatings that can be placed onto the surface, then removed using standard warm water pressure washing methods. This process was applied to an existing TAB process.