The effect of droplet ejection frequency on the dimensions of inkjet-etched micro-via holes in poly4(-vinyl phenol) thin films

Abstract

thin films and the number of ethanol drops dispensed was established for a range of droplet ejection frequencies. The physical mechanism underlying this relationship is proposed and the dependence of the development of via hole dimensions on the droplet ejection frequency is believed to be attributable to the extent of evaporation of the solvent between two consecutive drop dispenses. The results indicate complete penetration of the via holes through the polymer layer when produced at low droplet ejection frequencies. Electroplating was used to deposit Cu into the created holes to further confirm the absence of polymer residue at low frequencies. A threshold frequency, under which no via hole enlargement occurs, has been found. The study systematically focuses on the influence of droplet ejection frequency on the size of the inkjet-etched via holes versus the number of droplets used in poly(4-vinyl phenol) dielectric thin films for printed electronics application.

A mechanism of the penetration limit for producing holes in poly(4-vinyl phenol) films by inkjet etching

“…After several drops, the PVPh layer is completely etched through, resulting in a crater-like hole. The complete removal of polymer from the bottom of such via holes has been confirmed previously using an electroplating technique [28].…”

“…Even though it has been more than a decade since inkjet etching was first used to dissolve via holes for applications in electronics, it is still an underdeveloped method and more systematic investigations are needed to allow a detailed understanding of the underlying physics and chemistry. Previous work has identified the factors which influence the size of the inkjet-etched via holes and the penetration of the polymer layer [28,29]. It is postulated that using such a technique to fabricate via holes can only achieve a certain aspect ratio, i.e.…”

The penetration limit of poly(4-vinyl phenol) thin films for etching via holes by inkjet printing

“…Kawase et al 15,16 etched via holes in a polymer dielectric layer for interconnection using inkjet printing for making all plastic transistor circuits, owing to the coffee ring effect, during which materials loaded in solvents are carried to the contact line. 16,20,21,23,24 Few have studied the limitation of using inkjet etching to produce via holes in polymer layers. Via hole formation in polymer films by inkjet etching is through polymer dissolution and re-deposition, which is different from etching holes in silicon dioxide reported by Lennon et al, 25 where chemical reaction is involved and the soluble product can be washed away afterwards in water.…”

“…Nonetheless, failure to etch through a thick polymer layer by inkjet printing was demonstrated in our previous work using the polyacrylamide/deionized water system. 23 Therefore, it is postulated that a threshold polymer thickness exists, above which a 38.4 lm IPA droplet cannot completely penetrate the PVPh film in spite of the number of drops dispensed.This via hole formation is believed to comprise three processes: droplet impact and spreading, polymer dissolution, and solvent evaporation. When a droplet lands on the surface, it quickly wets into a sessile drop covering a contact area.…”

“…Xia and Friend 4,22 observed a thin polymer layer at the bottom of these holes after solvent evaporation and reported its removal by continuous solvent deposition. Kawase et al 16 and Zhang et al, 23 respectively, employed inkjet-printed test structures and electroplating technique to demonstrate that the holes could be etched through thoroughly. Up to date, investigations have been mainly focused on the relationships between printing parameters such as drop numbers and frequencies and via hole dimensions including diameters and hole depth.…”