Handbook of Solvents - George Wypych - ChemTech - Ventech!

14.8 Electronic industry 901
available on the market reveal an extremely wide process window. Almost all different
fluxes that occur in the electronic assembly process can be removed efficiently.
In principle, the media that can be used for semi-aqueous cleaning processes can be
classified into two main groups: 4
• solvent-based mixtures that are not soluble in water, and
• water-soluble cleaning fluids.
The water solubility of the solvent-based cleaning agent is very important for the treatment
of the subsequent water rinse.
14.8.2.2.1 Water insoluble cleaning fluids
The first media designed for this application were predominantly based on terpenes 13 and
different mixtures of hydrocarbons and esters. In order to increase the rinse ability of the
solvent-based mixtures with deionized water, different surfactants were added. 14 The principle
of using a water insoluble cleaning fluid was based on the idea to avoid contaminating
the rinse sections through the cleaning fluid. The lipophilic contamination should be kept in
the organic cleaning media that can be easily separated from the rinse water by a skimming
device. However, experience in the field revealed that this kind of media have some critical
drawbacks.
Since the surface tension of the organic cleaning formulations are lower than the surface
tension of deionized water (approx. 72 mN/m), the cleaning fluid stays on the surface
and will not rinse off. Consequently, the cleaning result is not acceptable with regard to
ionic contamination and surface resistivities. 1 Acceptable cleaning results can only be realized
through complicated multi-stage rinse processes. Another important disadvantage is
the potential risk of re-contamination of the substrate when lifting the substrate out of the
rinse section, since the top layer of the rinse section consists of polluted cleaning media.
Consequently, effective agitation and skimming of the rinse water is imperative to avoid
this phenomenon. 4
14.8.2.2.2 Water-soluble, water-based cleaning agents
The solvents used for this application are based on water soluble alcohols, alkoxypropanols
and aminoalcohols. 4,6 The chemical structure of these compounds combines a hydrophobic
and hydrophilic groups. Due to this ambivalent structure it is possible to optimize the water
solubility and lipophilic character for an optimal cleaning performance. Consequently,
cleaning fluids based on this principle reveal the largest process window. All different kinds
of flux residues, especially low rosin fluxes, are easily rinseable with water resulting in an
residue-free cleaning process. The quality and long-term stability of these processes are
proven through many applications in the field. 8,15,16 Applications and processes will be discussed
more detailed later on.
14.8.2.2.3 Comparison of the advantages (+) and disadvantages (-) of semiaqueous
cleaning fluids
In order to quantify the effectiveness of the two main groups of solvent based cleaning
agents that can be used for semi-aqueous processes, the following key aspects has to be
taken into consideration:
• cleaning performance,
• process reliability,
• environmental aspects, and