Because rosin oil has a long carbon chain, it is a resinous oil base; it cannot be cleaned with a general 12-carbon chain surfactant. From the picture below, you can clearly see the rosin flux residue after cleaning with a general cleaner.

Based on long carbon chain surfactants, we developed cleaning agent formula 1: in the chemical agent heated to 60~70 ℃, through a beaker, use 40Khz, 50W/L ultrasonic cleaning for 10 minutes, take it out, and rinse with water clean. Blow dry with air. It was found that the rosin flux residue had been removed.

Repeat the test, after 10 minutes of ultrasonic cleaning through the beaker, it is found that the rosin and flux residues have been removed.

After shortening the time test, after 5 minutes of ultrasonic cleaning through the beaker, it was found that the rosin and flux residues had been removed.

Repeated the test, after 5 minutes of ultrasonic cleaning through the beaker, it was found that the copper foil had changed color.

Shorten the test time and clean the beaker with ultrasonic waves for 3 minutes, and find that the rosin and flux residues have been removed. But the copper foil is still discolored.

Repeat the test, after 3 minutes of ultrasonic cleaning through the beaker, it is found that the residue of rosin flux has been removed. When there is no copper foil on the PCB, there is no difference before and after cleaning.

Based on formula 1, adjust the formula. Add antioxidants, ethanolamines, corrosion inhibitors...etc. Make recipes 2~6. It was found that the rosin flux residue can be removed, but it cannot prevent the discoloration of the copper foil.

Comparison: The one on the left in the picture below is after cleaning. The middle and right of the picture below are the colors of the copper foil before cleaning.

It was found that general long carbon chain surfactants could not inhibit the oxidative discoloration of copper foil. Formula 7 was developed by using hydrogenated amine fatty alkyl long carbon chain surfactant mixed with short carbon chain acetate surfactant to make the formula. It is found that this formula can inhibit the oxidation of aluminum alloy, and it can also inhibit the oxidation of copper foil, and has a good ability to remove flux.

Repeat the test. With formula 7, in the medicine heated to 60~70℃, through the beaker, use 40Khz, 50W/L ultrasonic wave to clean for 3 minutes, take it out, and rinse it with clean water. It was found that the rosin flux residue had been removed. And the copper foil did not change color.

Repeat the test. With formula 7, in the medicine heated to 60~70℃, through the beaker, use 40Khz, 50W/L ultrasonic wave to clean for 3 minutes, take it out, and rinse it with clean water. Blow dry with air. It is found that the flux has been completely cleaned after cleaning, but this PCB board has no copper foil, so it is impossible to determine whether the copper foil has changed color.

Results and discussion:

12.1 Formula 7 cleaning agent made of hydrogenated amine ester long carbon chain surfactant mixed with short carbon chain acetate surfactant can effectively remove flux and protect copper foil from oxidation and discoloration.
12.2 After cleaning with formula 7, although the copper foil will not be oxidized and discolored; but after cleaning, the copper foil itself will be gradually oxidized after being exposed to air for a long time. Therefore, if it is necessary to keep the color of the copper foil unchanged for a long time after cleaning, it is recommended to add 5~10% copper protectant COP01 in the last clean water, so as to maintain the luster of the copper foil for a long time.