Handbook of Solvents - George Wypych - ChemTech - Ventech!

918 Martin Hanek, Norbert Löw, Andreas Mühlbauer
tive tests may be required to furnish a more in-depth statement of regarding the condition of
the cleaning bath.
Refractive index:
An optical method by which a change of the refractive index of liquids, depending
upon the content of liquid or solid contaminants, is used to measure the level of bath contamination.
Solid residue from evaporation:
This method establishes the non-volatile residues in cleaning and rinsing baths. This
produces a very accurate statement of the bath contamination level.
Electrochemical potential:
The electrochemical potential is determined by the pH value, which furnishes an indirect
statement of the level of contamination.
Conductivity measurement:
This is used to check the quality of the rinsing bath in assembly cleaning processes.
The conductivity measurement indicates the amount of process-related ionic, and therefore
conductive, contaminants carried over into the rinse medium.
Ionic contamination measurement:
Ionic contamination-expressed in sodium chloride equivalents is primarily used to assess
the climatic resistance of electronic assemblies. Ionic measurement is suitable for statistical
process control, but it does not furnish an absolute statement concerning the climatic
resistance of an assembly.
Ink test:
Most organic residues on assemblies are not detected by ionic contamination meters.
However, such residues do change the surface tension of assemblies, thereby influencing
the adhesion of subsequent coatings. This method determines the surface tension by iterative
use of corresponding testing inks.
Furthermore, the remaining protective ability of organic solder (OSP-coatings) on
copper can be estimated. This test also provides an indication of the adhesion of lacquers
and conformal coatings to the assembly.
Water-immersion test:
This economical test exposes the climatically unstable points of electronic components.
Due to the nature of the test, the entire board is evaluated. This test accelerates the
mechanisms of electrochemical migration. Consequently, faults that previously would appear
after months or even years can be detected during the development process. To identify
potential weak points, the assembly is operated in standby mode and immersed in deionized
water. Testing while the assembly is in full operation is even more effective. The sensitivity
of the circuit to moisture exposure is assessed on the basis of the recorded test current, combined
with a subsequent examination of the assembly. Through weak point analysis, a
Yes/No decision can be determined concerning the expected service life, of the assembly.
The growing diversity of cleaning media, cleaning equipment, and cleaning processes,
together with more stringent legal requirements and quality expectations, are making it increasingly
difficult for companies to develop their own cost-effective and result-optimized
cleaning processes. Consequently, a lot of well known manufacturing companies opted for
turnkey solutions for the entire development and installation of complete cleaning processes.