Adhesion evaluation of adhesiveless metal/polyimide substrate for MCM and high density packaging
Directly metallized polyimide films are being widely used as advanced high-density packaging substrates. Adhesion of metal to polyimide is a key performance requirement of the film. Excellent initial adhesion and good retention after severe process steps and reliability stresses are required. In this paper, the adhesion performances of films with different types of polyimide and tie layer from multiple vendors have been evaluated. The interface failure mechanisms are also examined via SEM micrographs and XPS survey scans. Peel strength and its retention behaviour are characterized in term of tie layer materials, environmental stresses and surface analysis results. The object of this work is to select the proper base material for high-density flexible multilayer substrates, a technology which is under development by FCPT.
Latest advancement of fully additive process for 8 µm ultra-fine pitch chip-on-film (COF) by nano-size Ni–P metallization
This paper presents the first demonstration of a precision formation of conductor patterns as fine as 8 µm pitch for flex-based electronics assemblies. We have developed a novel fully additive process (FAP) by combining an ultra-thin chemical surface modification on polyimide (PI) to achieve a uniform Ni–P metallization and subsequent high-speed electrolytic pattern copper plating. On top of the modified interface, an ultra-thin anchoring layer (< 5 nm) constituting amide and carboxyl bonding is able to compensate the hydrophilic nature of the modification layer to obtain reliable adhesion even after being subjected to 300 °C heat treatment, as verified by XPS and TEM analysis at 1000kX. This exceptional property eliminates the trade-off concern by achieving both high-speed signal transmission and enhanced interfacial bond strength on a smooth surface (Ra < 60 nm). Experimental results revealed that the bending endurance and trace deformation characteristic of the fine pitch circuit by this FAP is comparable to conventional COF substrates and is also able to produce high-quality diffusion bonds with the formation of nano-twin structure on the Au–Au bonding interface. Insulation resistance measurements showed no metal residues and no current leakage between 16, 20, and 25 µm pitch COF after temperature humidity bias. On the basis of these results, FAP by direct Ni–P metallization proposed in this work provides unique opportunities for ultra-fine pitch and high electrical performance interconnects.
XPS Study of Polyimide H-Film After Heat Treatment and Laser Processing
An x-ray photoelectron spectroscopy (XPS) study of laser treated and heat treated Kapton ® indicates that both the treatments result in depleting the carbonyl groups from the sample and leave behind a conducting residue that still contains significant amounts of oxygen and nitrogen. The rapid changes in surface composition coincide with a substantial decrease in the electrical resistivity of the polyimide samples.