"Cleaning" is often ignored in PCBA manufacturing process, and it is considered that cleaning is not the key step. However, with the long-term use of the product in the client, the problems caused by the invalid cleaning in the early stage cause many failures, and the repair or recall of the product results in a sharp increase in operating costs. The following is a brief description of the role of PCB cleaning.
PCBA (printed circuit assembly) production process goes through many process stages, each stage is polluted to different degrees, so PCBA surface remains various deposits or impurities, these pollutants will reduce product performance, and even cause product failure. For example, in the process of welding electronic components, solder paste and flux are used for auxiliary welding, resulting in residues after welding, which contain organic acids and ions, among which organic acids will corrode PCBA of circuit board (circuit board), while the presence of electric ions may cause short circuit, resulting in product failure.
There are many kinds of pollutants on PCBA, which can be classified into two categories: ionic and non-ionic. When the ionic pollutants contact with the humidity in the environment, electrochemical migration occurs after power on, forming a dendrite structure, resulting in a low resistance path and damaging the PCBA function of circuit board (circuit board). Nonionic pollutants can penetrate the insulating layer of PC B and grow dendrites under the surface of PCB. In addition to ionic and non-ionic pollutants, there are also granular pollutants, such as solder ball, floating point in solder groove, dust, dust and so on. These pollutants will lead to poor quality of solder joint, solder joint pulling during welding, air hole, short circuit and other adverse phenomena.
So many pollutants, which are the most concerned? Flux or solder paste are widely used in reflow soldering and wave soldering. They are mainly composed of solvent, wetting agent, resin, corrosion inhibitor, activator and other components. There must be thermal modification products after welding. These substances are dominant in all pollutants. In terms of product failure, post welding residue is the most important factor affecting product quality, and ionic residue is the most important one It is easy to cause electromigration and decrease the insulation resistance. Rosin resin residues are easy to absorb dust or impurities and increase the contact resistance. In serious cases, it will lead to open circuit failure. Therefore, strict cleaning must be carried out after welding to ensure the quality of PCBA.
To sum up, PCBA cleaning is very important, "cleaning" is an important process directly related to PCBA quality, which is indispensable
Oct 03, 2019
