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36 SMT Magazine • January 2015 ous and aqueous cleaning technologies were initially favored to replace CFCs because of their lack of flammability, low price and avail- ability. However, with the advances in PCB de- sign, it has become apparent that the relatively high surface tension of water makes it difficult to penetrate in narrower spacing. The corro- sive nature of water can also be problematic. In addition, drying is very energy-intensive and wastewater disposal brings in difficulty and ex- pense in operation. In the case of semi-aqueous techniques, these same problems occur, in addi- tion to odor and some flammability issues that users have to deal with. Azeotropic mixtures of HCFC-225 (dichlo- ropentafluoropropane) isomers and HCFC- 141b (1,1-dichloro-1-fluoroethane) with al- cohols were adopted by many users at the outset for defluxing and degreasing applica- tions. They were actually drop-in substitutes for CFC-113. However, these compounds have lower ozone depletion potential than CFCs but are still not acceptable due to their non-zero ozone depletion potential. As a result, 141b was phased out in early 2000, and HCFC-225 isomers will be phased out starting January 1, 2015. Users have realized a need to adapt new technologies or new solvents to replace these materials. HFCs and HFEs are introduced; how - ever, they do not have sufficient solvency to be used alone. A chlorinated hydrocarbon, tr-1,2-dichloroethylene, had to be added to these materials to boost their solvency, while alcohols have also been added to remove ionic contaminants. Among the not-in-kind technologies, the use of no-clean fluxes to avoid post-soldering cleaning altogether is worth discussing. Such no-clean fluxes with lower ionics are used by many people in the industry. While the use of such materials would in theory have eliminated the need for post-soldering cleaning altogether, it was found that for many applications, post- soldering cleaning is still required in order to preserve long-term reliability of the electronic components and to improve visual appearance of the boards by removing residues. As a result, it is common that no-clean fluxes need to be cleaned after soldering. Other technologies such as supercritical cleaning with CO 2 , CO 2 snow, plasma cleaning technologies are also available in cleaning, but they are not generally used in defluxing applications. With these challenges in the industry, the company recognized the need for better sol- vents and technology in cleaning and defluxing. A new generation of compounds, hydrochloro- fluoro olefins and hydrofluoroolefins have been identified and developed for various applica- tions including refrigeration and air condition- ing, foam expansion agents and some solvent applications. The new 1233zd(E) is one such compound that is particularly well suited for solvent cleaning which we shall discuss below. new Solvent Structure and Properties The molecular structure of this new solvent 1233zd(E) is shown in Figure 1. A versatile next-generation solvent must satisfy a complex mosaic of properties. One of Figure 1: Chemical structure of solvent 1233zd(e). • Molecular Formula: cF 3 cH=cHcl • iupAC Name: (e ) 1-chloro-3,3,3-trifluoro- 1-propene • Refrigerant Number: R-1233zd(e) • Trans of e (entgegen) isomer an aLTErnaTIvE SOLvEnT WITH LOW GLOBaL WarMInG POTEnTIaL continues artiCle