Handbook of Solvents - George Wypych - ChemTech - Ventech!

896 Martin Hanek, Norbert Löw, Andreas Mühlbauer
After the decision has been made in order to choose the most suitable cleaning process,
the following two questions have to be answered in advance:
• Which contamination has to be removed?
• What are the requirements regarding cleanliness of the surface, especially taking the
subsequent process steps into account.
The most important consideration in
achieving an optimal cleaning result, is the
interaction between the chemistry of the
cleaning agent and the type of contamination.
This is explicitly shown in the below
presented lock and key principle.
However, the cleaning result is not
only depended on the nature of the chemistry
used for cleaning. Other important factors
in the cleaning process are the type of
cleaning equipment used and the applied
Figure 14.8.2. Factors influencing the cleaning process.
process parameters such as temperature,
time and method of application of the cleaning
agent (see Figure 14.8.2).
In order to optimize a cleaning process for the specific requirements, detailed informa-
tion on the nature and composition of the kind of contamination that has to be removed is
necessary. This tailoring of the chemistry is achieved by carrying out time consuming
screenings matching typical contamination with suitable solvents.
Another very important aspect is the material compatibility of the cleaning agent and
the substrates that need to be cleaned. The cleaning chemistry should not attack the different
materials of the components in any manner. Consequently, a number of long-term compatibility
tests have to be carried out to assure this very important process requirement.
Also, more environmental and worker safety issues are ever increasing when evaluating
a new cleaning process. Cleaning processes approved by the industry have to pass even
higher standards than are demanded from the government. They have to show, under the
worst case scenario, a large process window and a large process margin of safety with respect
to personal and environmental exposure.
If all of the above mentioned process requirements such as
• excellent cleaning result,
• long-term functional reliability of the substrates after cleaning,
• material compatibility between cleaning chemistry and the substrates, and
• no drawbacks due to environmental and safety issues
should be fulfilled, a lot of time and know-how has to be invested.
14.8.2 AVAILABLE ALTERNATIVES
Due to the global ban of the CFCs, a large number of different cleaning processes 4 have
been developed. Each of them has advantages and disadvantages regarding the above mentioned
process requirements. The available cleaning processes can be divided into the following
main groups:
1) aqueous processes,
2) semi-aqueous processes,
3) water-free processes based on solvents, and