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Cleaning technology of printed circuit board
Nov 17, 2018

Water base cleaning process

The water-based cleaning process takes water as the cleaning medium. In order to improve the cleaning effect, a small amount of chemicals such as surfactants, washing auxiliaries and corrosion inhibitors can be added into the water (generally 2-10%).According to the specific conditions of pollution of different properties on the printed circuit board, additives in water-based cleaning agent can be used to make the cleaning more applicable scope.The water-based cleaning agent has a good dissolving effect on water-soluble dirt, and then combined with physical cleaning means such as heating, scrubbing, spraying, ultrasonic cleaning and so on, it can achieve better cleaning effect.Adding surfactant to the water-based cleaning agent can greatly reduce the surface tension of water, strengthen the penetration and spreading ability of water-based cleaning agent, and better penetrate into the gaps between tightly arranged electronic components, and clean the dirt infiltrating into the substrate of printed circuit board.The solubility of water and emulsion dispersion of surfactants can also be used to remove the residues of synthetic active flux, which can not only dissolve all kinds of water-soluble dirt, but also remove non-soluble dirt such as synthetic resin and fat.Saponifier is a chemical used to saponify organic acids, such as rosin acid and fatty acid in oil, in cleaning printed circuit boards when appropriate saponifier is added into rosin flux or water-based cleaning agent.This is a common ingredient in many flux and grease detergents used to clean printed circuit boards.Saponifier is usually alkaline inorganic matter such as sodium hydroxide, potassium hydroxide and other strong alkali, also may be alkaline organic matter such as monoethanolamine.Organic solvents and surfactant components are commonly used in commercial saponifiers to clean out residues that cannot be saponified.The saponifier may corrode the aluminum, zinc and other metals on the printed circuit board.Therefore, corrosion inhibitors should be added in the formula.However, it should be noted that the printed circuit board which is sensitive to alkaline substances should not be cleaned with water based cleaning agent containing saponifier. 

In the process of water base cleaning, if the ultrasonic cleaning is used together with the ultrasonic cleaning, the "hole effect" caused by a large number of tiny air bubbles during the transmission process of the cleaning liquid can effectively remove the insoluble dirt from the electronic junction plate.Considering the solubility requirements of printed circuit board, electronic components and ultrasonic wave, the ultrasonic frequency used in the cleaning of printed circuit board is generally around 40KHz. 

Water base cleaning process includes washing, rinsing and drying.First, the printed circuit board was cleaned in batches by using a water-based cleaning agent with a concentration of 2-10%, combined with physical cleaning means such as heating, scrubbing, spraying, ultrasonic cleaning, etc., and then the printed circuit board was rinsed with pure water or ionized water (DI water) for 2-3 times, followed by hot air drying.The high cost of water base cleaning is caused by the need to use pure water for rinsing.Although high quality water quality is a reliable guarantee of cleaning quality, in some cases, it can be achieved by first rinsing with the low-cost electric conductivity in the deionized water of 5um·cm, and finally rinsing with the high purity of electric conductivity in 18um·cm.Typical water cleaning process is shown in figure 1.A typical technological process is: under the temperature of 55 ℃ with water-based cleaning agent to batch cleaning of electronic circuit boards, and cooperate with the powerful jet cleaning 5 min, rinse thoroughly with 55 ℃ deionized water for 15 min, finally at 60 ℃ temperature hot air blow dry 20 min.In order to improve the utilization rate of water resources, the tap water used in the cleaning process or the deionized water used in the rinsing tank, according to the literature, the use of tap water (hard water with more ions) in the pre-cleaning can not only greatly reduce the production cost, but also its decontamination capacity is no worse than soft water or deionized water.