Epoxy resin smudges produced during drilling and cleaning of circuit boards will interfere with the bonding force between the electroless copper plating layer and the substrate. Ordinary double-sided boards can be cleaned by means of high-pressure water washing or high-pressure wet sandblasting. It is still far from enough for multi-layer circuit boards or circuit boards with high board thickness/aperture ratio.

Resin dirt on the copper ring inside the multilayer circuit board will hinder the stability of the inner layer connection, so it must be completely removed. There are two ways to remove epoxy resin drill stains: dry method and wet method:

(1) Dry cleaning

The epoxy drilling contamination in the hole wall is removed by means of plasma in a vacuum environment. This method requires special plasma cleaning equipment. The disadvantage is that the production efficiency is low and the cleaning cost is high. Only under special conditions, such as flexible multi-layer circuit boards, rigid-flex multi-layer circuit boards, polyimide and more Used when layering circuit boards.

(2) Wet cleaning

Including concentrated sulfuric acid, concentrated chromic acid, alkaline potassium permanganate cleaning these three. Chromic acid is prone to serious ecological and environmental problems, which is obviously not desirable in this era of increasing environmental awareness. The most common cleaning methods are concentrated sulfuric acid and alkaline potassium permanganate. The following is a detailed explanation of the treatment method of concentrated sulfuric acid and alkaline potassium permanganate!

1. Concentrated sulfuric acid treatment

One of the major advantages of concentrated sulfuric acid is that it has strong oxidizing properties and water absorption, which can carbonize epoxy resins and generate water-soluble alkyl sulfonates to remove drill stains. The decontamination effect depends on the concentration of concentrated sulfuric acid, treatment time, solution temperature and other factors. Treatment requires that the concentration of concentrated sulfuric acid must be above 86%. If etching is required, the solution temperature and cleaning time should be adjusted reasonably.

Concentrated sulfuric acid only has an effect on the epoxy resin on the hole wall, and is ineffective on glass fiber. When using concentrated sulfuric acid to etch the multi-layer circuit board, the glass fiber head will protrude from the hole wall. At this time, fluoride should be used to clean it. When using fluoride to clean the protruding glass fiber head, it is also necessary to control the process conditions to avoid the wicking effect caused by the excessive corrosion of the glass fiber. pcb proofing circuit board

Multilayer circuit board

2. Alkaline potassium permanganate treatment

After the concentrated sulfuric acid dissolves the epoxy resin, the resin surface of the hole wall becomes too smooth, which seriously affects the bonding force of the electroless copper plating layer. Thus, the alkaline potassium permanganate treatment method was born. This method can not only remove the epoxy resin contamination, but also can etch the epoxy resin surface to produce uneven pits, so as to enhance the bonding force between the hole wall coating and the substrate. In addition, the absorption of the activator is enhanced, which greatly reduces the problem of cavities and blow holes.

The alkaline potassium permanganate treatment is carried out in three steps:

The initial swelling treatment is to use an organic solvent to swell the epoxy resin. The next step is called potassium permanganate oxidation treatment. It refers to the oxidative removal of the swollen epoxy resin by means of potassium permanganate under the condition of high temperature and high alkali. The production of manganate and MnO2 will affect the activity and oxidation capacity of the solution. We usually convert manganate into permanganate with strong oxidizing ability by means of electrolysis or adding regenerated salt, and MnO2 can be removed by circulating filtration. The second step of neutralization treatment is to reduce the permanganate produced by the circuit board and completely remove the residual manganese dioxide, manganate, and permanganate in the pores. High precision pcb circuit board

The pcb circuit board is a vital interconnection of electronic products, which is also an outstanding product of modern development. The pcb circuit board is also called the mother of electronic products, because in electronic products, the most special thing is our pcb circuit board. Without the pcb circuit board, the assembly of electrical components cannot be connected and assembled normally. pcb proofing circuit board