Solvents and Cleaners in Electronics
Publication Date: 2014-Jul-18
The IP.com Prior Art Database
Use of new solvents made from renewable sources in electronics applications, in particular in resist stripping compositions. The new solvents are acetals like 2,2-dimethyl-1,3-dioxolane-4-methanol (CAS Nº 100-79-8), 2-isobutyl-2-methyl-1,3-dioxolane-4-methanol (CAS Nº 5660-53-7) and 2,2-dimethyl-1,3-dioxolane-4-acetate (CAS Nº 14739-11-8), as they are able to replace known solvents like halogenated hydrocarbons, amines, glycol ethers, alcohols and ketones that are flammable, volatile, odoreous and toxics. Indeed, the acetals listed above have no odor, aren´t flammable, are stable in the presence of amines, have low toxicity, aren´t bio-accumulative and have low carbon footprint, when compared to solvents with similar solubility performance, that were mentioned above. Moreover, the acetals ensue the solubilization of the most used resins of this market and the elimination of flux residues, greases, particles and any other residue from the lithography process. They also ensure good bonding and no corrosion, maintaining stability during time, efficiency, quality and performance.
The constant search for sustainable alternatives in several fields of the chemical industry, such as mining, pharmaceutical, agro, paints & coatings, leather, home & personal care, construction, actives solubilization, etc, led to development of solvents that meet the three pillars of sustainability (economical, environmental and social). Such solvents present competitiveness, very good performance in the application, and additionally low toxicity to humans and environment. One application where those solvents can be used is in electronics, as a component at the lithography process, but mainly as stripper and cleaner.
Lithography is the process that includes a number of methods for replicating a predetermined pattern on a substrate, which is, in most cases, effected by first coating the substrate with a photosensitive polymer film called a lithographic resist, and then exposing the film to a pattern of light. (1) This photoresist system is composed mainly by resins like phenol formaldehyde, modified epoxy and PMMA (15-25%), solvent (65-85%), photo active compounds (~5%) and several additives. The main function of the solvent is to act as a carrier and thinner of the whole system, so the solvency power is of extremely importance.
In certain applications, the resist film becomes a permanent, functional component of the device being constructed, typically serving as an electrical insulator or protective encapsulant. Most commonly, however, the resist pattern is a temporary template, and is removed or stripped after the image has been transferred to the substrate. (1) It is necessary that the photoresist material be evenly and completely removed from all unexposed areas, so as to permit further operations.
Examples of the solvents that are most commonly used for cleaning and/or stripping are halogenated hydrocarbons, such a methylene chloride, amines and their derivatives such as dimethylsulfide, dimethylformamide, N-methyl-2-pyrrolidinone, glycol ethers such as ethylene glycol monomethyl ether, ethanol and the acetates thereof; ketones such as methyl ethyl ketone and acetone, as well as various other materials. One of the major disadvan...