Laser direct imaging of the printed electrical circuits on PCB

Abstract

The increasing demands for miniaturization and better functionality of electronic components and devices have a significant effect on the requirements facing the Printed Circuit Board (PCB) industry. PCB manufactures are driving for producing high density interconnect (HDI) boards at significantly reduced cost and reduced implementation time. The interconnection complexity of the PCB is still growing and today calls for 50/50 μm or 25/25 μm technology are real. Imaging of HDI boards poses a rapid increasing challenge on PCB manufactures due to line width and space getting smaller and mainly to tighter registration requirements. Existing technologies are unable to offer the acceptable solution. Nowadays the Laser Direct Imaging (LDI) technology is considered as an answer for these challenges. LDI is a process of imaging circuitry pattern directly on the PCB without the use of a phototool. The exposure of the photo-sensitive resist is carried out using a laser beam that is scanned across photoresist surface and switched on and off by means of a computer control system according to the electrical circuit pattern. Usually the laser used in the LDI generates the UV line, which is suitable for the commonly available photoresists. In this paper we present an introduction to LDI technology as well as an experiment consisted in an attempt to use a UV Nd:YAG laser (λ=355 nm) for direct imaging of conductive pattern on the PCB covered by photosensitive resist.