Fine pitch thin film processing on flex substrates
Abstract
A Swedish research institute has built up a resource for thin film high density interconnect processing on flexible substrates. The substrate material is spun on a rigid carrier, with further processing consisting of metalization, metal patterning, insulator deposition and via formation in a multi-layer sandwich structure. The institute is offering process and prototype development of custom designed, flex based, circuits and modules.
Description
By spin coating polyimide, or a similar material, onto a rigid carrier, a thin, flexible substrate is created. The polymer film is attached to the carrier throughout the processing, and finally removed. On top of the polymer film, a thin metal layer (e g Al or Cu) is deposited and patterned, using traditional photolithography and wet metal etching techniques.
Typical line widths is around 10 - 25 µm, but, if desired, smaller structures are possible to achieve.
On top of the patterned metal, a second polymer layer is spun, in which via holes are created, by means of dry ion etching. This way, several layers of metal and dielectric are built up to a stack. The multilayer structures can for instance be used for miniaturized flexible circuit boards.
Carrier plates of up to 6" in size (circular or square) are possible.
Innovative Aspects:
Traditional flex processes are based on regular printing on a solid polymer foil, glued or taped onto a rigid carrier. Poor planarity, combined with the limitations of a printing technique, reduces the possibility for fine pitch patterning. With the present technique, this problem is solved. Also, the polymer material used as dielectric (via) layers can be used as substrate material.
