TABLE OF CONTENTS Cleaning, as it relates to soldering, has a double purpose. As we saw earlier, for a flux in a solder system to wet, presolder cleaning is vital (Sec. 5.11). In this chapter, we will deal with cleanliness in general and concentrate on flux removal in particular.
The importance of postsoldering cleanliness is undisputed throughout the industry, and unless materials and processes are specifically selected to eliminate this operation, serious trouble may ensue. These can further be divided as follows.
Corrosion problems from aggressive fluxes, which leave residues that will attack structural members and may cause total failure (Sec. 1.14).
Electrical problems when soldering is used on electronic assemblies. Here, flux residues and possible corrosion products may contain ionic contamination, which will lead to current leakage under humid conditions (see Sec. 1.15).
While it is difficult to give a general guide to the level of cleanliness to which any type of electronic assembly must conform, cleanliness requirements for military and government contracts have been established. Details on methods of monitoring cleanliness and the physical equipment available are given later in this chapter.
There is another important factor that induced cleaning in soldering. As the complexity of printed circuits grew, bed-of-nails testing became part of the assembly and soldering process. Bed of nails is a method that allowed multiple solder joint probing with electrical contacts (the nails) to test the assembly. This test helped verify component values, polarity, and circuit integrity. Flux residues posed...
