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Handbook of Solvents - George Wypych - ChemTech - Ventech!

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900 Martin Hanek, Norbert Löw, Andreas Mühlbauert<br />

3) Environmental aspects<br />

A cleaning agent should not only be considered based on its content <strong>of</strong> volatile organic<br />

compounds. A medium that does not contain any VOCs may on the one hand have no influence<br />

on air pollution. However, on the other hand, soil and water may be influenced. A<br />

VOC containing cleaning fluid has an inherently longer bath life. Consequently, the overall<br />

environmental calculation for some VOC containing cleaning fluid are better than by using<br />

VOC-free media.<br />

4) Personal safety<br />

Another very important aspect for the evaluation <strong>of</strong> a new cleaning process is the issue<br />

on personal safety. The following topics have to be taken into consideration:<br />

• No risks during handling <strong>of</strong> the cleaning agent, especially regarding toxicity and<br />

flash point.<br />

• Low odor <strong>of</strong> the cleaning fluid.<br />

If the evaluated cleaning agent fulfils these important requirements, the chemistry will<br />

be accepted by the operator.<br />

Taking the discussed issues (1-4) into account, the advantages (+) and disadvantages<br />

(-) for the different aqueous cleaning fluids are as follows:<br />

a) Aqueous fluids using amines for saponification:<br />

+ excellent removal <strong>of</strong> flux residues and unsoldered solder paste<br />

+ predominantly VOC-free formulations<br />

- low solid flux residues are difficult to remove<br />

- limited removal <strong>of</strong> adhesives due to curing <strong>of</strong> the adhesive<br />

- short bath life times resulting in high costs for media disposal<br />

b) Aqueous fluids using inorganic saponifiers and buffer systems:<br />

+ satisfying cleaning results on flux residues and solder paste<br />

+ VOC-free formulations<br />

+ longer bath life due to constant pH level caused by the buffering<br />

systems<br />

- low solid flux residues and SMT adhesives are difficult to remove<br />

c) Mixtures <strong>of</strong> organic solvents and water:<br />

- small process window regarding flux residues and SMT adhesives<br />

- VOC containing mixtures<br />

- short bath life<br />

d) pH neutral and alkaline fluids based on MPC � Technology:<br />

+ extremely large process window regarding flux residues, solder<br />

paste and adhesive removal<br />

+ extremely long bath life-times due to previous described cleaning<br />

principle<br />

+ economical cleaning process<br />

- small amounts <strong>of</strong> VOCs.<br />

14.8.2.2 Semi-aqueous cleaners based on halogen-free solvents,<br />

advantages and disadvantages<br />

A semi-aqueous cleaning process consists <strong>of</strong> a wash cycle using a mixture <strong>of</strong> different organic<br />

solvents followed by a rinse with deionized water. Organic contaminations, predominantly<br />

rosin flux residues, are removed through the lipophilic solvents, whereas the ionics<br />

are minimized by the polar rinse media. The different kinds <strong>of</strong> solvent formulations that are

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