The patterning of fine-pitch electrical interconnections on non-planar substrates: a comparison between methods utilising laser ablation and electro-deposited photoresist

Abstract

This paper compares and contrasts two methods that we have developed for patterning fine-pitch, electrical interconnections onto grossly non-planar surfaces. The first method involves the selective ablation of nickel using a YAG laser. The optimisation of the laser process is discussed. The second method employs an electro-depositable photoresist (EDPR) (Shipley PEPR2400) to pattern a copper seed layer that is then overplated with nickel. The substrate studied is a piezo-electric ink-jet print head that requires up to one thousand 80 μm-pitch interconnections over a step height of 500 μm. The two technologies are found to be complementary, with laser patterning offering greater flexibility for product development and EDPR patterning offering a higher throughput for mass-production.