SMT007 Magazine

SMT-Jan2015

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34 SMT Magazine • January 2015 which ultimately led to the Montreal Protocol [2] being ratified by the United Nations Environ- mental Program (UNEP) in 1987, which phased out CFCs around the world. Rowland and Mo- lina received the Nobel Prize for Chemistry in 1995 for their discovery. This discovery of stratospheric ozone deple- tion shocked the world and brought an end to CFCs' use as cleaning solvents, working fluids in refrigeration and air conditioning, foam expan- sion agents, and in various other applications. CFC-113 (1,1,2-trichloro-1,2,2-trifluoro-ethane) and 1,1,1-trichloroethane were previously used extensively in industrial cleaning. The PCB in- dustry primarily used CFC-113 in cleaning solder fluxes and pastes after soldering and set the standards of cleaning for the boards. These solvents also found applications in metal degreasing, precision clean- ing of aerospace components, cleaning of medical devices and in many other cleaning applications because of their high solvency for common soils, low toxicity, non-flam- mability and many other de- sirable properties. Since the phase-out of these solvents in 1996, the solvent market has become extremely fragment- ed, with industrial customers using many different solvents for each specific application. No single solvent has been found that can be used effec- tively for as many applications in the same way as CFC-113 and 1,1,1-trichloro- ethane. In this article, we will discuss a new cleaning solvent and some of the successes it has had in cleaning. The chemical name of this new solvent is trans-1-chloro-3,3,3-trifluoro- 1-propene. Using the numbering system of ha- logenated compounds [3] it can also be referred to as 1233zd(E); the E in parentheses indicates it is the trans configuration of the molecule. It has been found to be as good as CFC-113 in dis- solving and cleaning most common soils, but it provides superior environmental properties. We will describe the properties and perfor- mance of this solvent in greater detail including its cleaning efficacy, environmental properties, stability under various conditions, along with its recovery by carbon adsorption and compat- ibility with plastics and elastomers, and com- pare them with some of the solvents used today. Background Cleaning technologies used today can be di- vided into a few major categories: solvent clean- ing, aqueous cleaning, semi-aqueous cleaning, and not-in-kind, which include no-clean fluxes and supercritical cleaning, among others. Sol- vent cleaning includes various hy- drocarbons, halogenated hydro- carbons, hydrofloroethers and several others, and blends of these materials with alcohols and other compounds. Aque- ous cleaning refers to cleaning with water and various deter- gents; semi-aqueous refers to the removal of soils with ter- pene or citrus-based solvents and then washing these mate- rials with water. None of these cleaning alternatives became a universal alternative to CFC-113 in cleaning. A large section of the PCB cleaning industry is using aqueous sol- vents and a number of water- soluble fluxes have also been introduced. However, aqueous cleaning has not been able to solve all the cleaning problems especially those in the defense and aerospace industries. As technology in PCB design is advancing, line spacing is becoming narrower, components are being spaced closer to the boards, and more surface mount devices are being used. All of these factors are making cleaning PCBs more difficult, leaving a need for better solvents and technologies. Now, going into some issues with existing technology, we can see that hydrocarbon-based solvents are flammable, which makes handling and use of such materials difficult. Semi-aque- an aLTErnaTIvE SOLvEnT WITH LOW GLOBaL WarMInG POTEnTIaL continues a large section of the PCB cleaning industry is using aqueous solvents and a number of water- soluble fluxes have also been introduced. however, aqueous cleaning has not been able to solve all the cleaning problems especially those in the defense and aerospace industries. " " artiCle

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