Printed-wiring boards cleaning

Many of the fabrication processes for integrated circuits are similar or conceptually related to those used in the manufacture of printed wiring boards. However, because of the extremely fine device features, fabrication must be carried out in clean rooms having strictly controlled environments. Particulate and chemical contamination are minimized, and temperature, humidity, and even vibration are carefully controlled. 

These steps are enumerated and described in Chapter 1.2. Operation of superheat in open-top vapor degreasers is explained in Chapter 1.20 For reference, solvent cleaning operations with trichloroethylene and n-propyl bromide are conducted at their boiling points - 86°C (187"F) and 71"C (160°F), respectively. It is this author s experience that Class II cosolvent processes have found more interest in Europe than in the US. The chief application is removal of flux residues from printed wire boards (PWBs). 

Table 4.4 lists commercial cleaning solutions currently used in the electronics industry for cleaning printed-circuit boards, assemblies, ceramic printed circuits, thick-film interconnect substrates, electronic components, wiring harnesses, and stencils and screens (used in applying adhesives and solder pastes). 

The printed circuit boards and the various electronic components to be added to it are cleaned, trimmed and sorted. The components are then mounted on to the printed circuit board ( stuffing ). This can be done either by hand or by automated surface mount machines. The parts are then soldered on to the board, by immersion in wave solder baths, or by hand. Excess solder and wire is removed by hand in a touching-up process. The final product is marked and tested in a quality control check. 

Those applications were for removal of acidic flux and flux residues from various printed circuit (wire) boards (PWBs), removal of camauba wax from optic materials, removal of buffing and lapping compounds from metal substrates, and some others. These applications share at least one characteristic — that high quality, thoroughly repeatable cleaning is essential. And these applications remain highly valued. 

The details of these materials are discussed in other chapters. However, it is important to understand their role in the overall circuit board assembly process. First of all, the functions of these three materials require that they have good adhesion to all surfaces. Therefore, the printed wiring assembly must be cleaned of any flux residues as well as those residues left behind from the cleaning procedure. 

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