The post-treatment of the heat sink housing surface refers to the filling, surge, and powder spraying of the internal anti-corrosion paint.
Common defects are as follows:
The internal anti-corrosion cannot be hung up. Because of poor pre-treatment effect or improper coating configuration, the welding area is directly exposed to water & corrosion occurs.
After drying, there are honeycombs or cracks on the internal anti-corrosion end. If the inner cavity is wet and full of anti-corrosion paint, water will evaporate. The raw material of water-based paint, the ratio problem, too much water/ethanol can also cause evaporation. Solvent-based internal anti-corrosion coatings increase the boiling point. If the solvent content is lower, the time in the mold cavity is shorter, which will cause the solvent to evaporate rapidly during the baking process, and honeycomb holes will appear. Thus, after filling the paint, it requires at least 1 hour and air-dried as soon as possible.
Many cases of heat sink housing cracks cause by local accumulation of paint that is too thick and not fully cured. The upper part solidifies, while the lower part is still evaporating the solvent, causing cracks.
Above drawbacks, impurity ions in water infiltration/accumulation/fouling. Or the accumulation of scale inhibitors (acid or alkali) added to the water will cause faster corrosion.
Internal anti-corrosion, no adhesion. The internal anti-corrosive resin and filler are important.
With less resin, the film becomes brittle and not smooth, which will reduce the corrosion resistance.
The filler fineness is insufficient, and many uneven particles appear in the film. Large particles are easily washed away and cause pitting corrosion.
The filler grade is too low, resulting in the film thickness does not increase, the hiding power reduces, the hardness is insufficient, and the corrosion resistance being reduced.
The defects of the outer coating include broken wires, cracks on the exposed bottom, serious orange wires, pinholes, small cracks, etc. Under normal circumstances, the material is too poor, the pre-treatment is unqualified, and the heat sink processing technology is unqualified. Due to the long development time of powder coatings, plastic powders above the medium level will not have quality problems.