The method of removing the unqualified electroless nickel coating on PCB

The removal of electroless nickel coating is much more difficult than electroplating, especially for high corrosion resistance electroless nickel coating. The unqualified electroless nickel coating should be removed before heat treatment, otherwise the passivation of the coating is more difficult. It is required that the stripping solution must have no corrosion to the substrate, and then the coating thickness, stripping speed, stripping cost and other factors should be considered.

(1) Electroless deplating method:

The electroless stripping method does not corrode the workpiece, and is suitable for the workpiece with complex geometry, and can achieve uniform stripping.

Formula 1: concentrated HNO3, 20 ~ 60 ℃. This solution has the advantages of low cost, high speed (30-40 μ M / h) and low toxicity. It is suitable for the stripping of workpieces with low precision requirements to prevent water from being brought in. After stripping, it should be cleaned in hydrochloric acid and then cleaned with flowing water.

Formula 2: HNO3 (1 ∶ 1), 20-40 ℃, fast regression (10 μ M / 5-6min), suitable for stainless steel.

Formula 3: concentrated HNO3 1000ml / L, NaCl 20g / L, urea 10g / L (inhibiting the formation of NOx gas), hexamethylenetetramine 5g / L, room temperature, regression rate 20 μ M / h.

Formula 4: sodium m-nitrobenzenesulfonate 60 ~ 70g / L, sulfuric acid 100 ~ 120g / L, potassium thiocyanate 0.5 ~ 1g / L, 80 ~ 90, suitable for copper and copper alloy workpiece stripping. When the stripping surface is dark brown, take it out and clean it thoroughly, then remove the brown film (NaCN 30g / L, NaOH 30g / L, room temperature).

Formula 5: HNO3 ∶ HF = 4 ∶ 1 (volume ratio), heating properly in winter, fast regression, no corrosion of iron matrix. However, HF must be analytically pure.

Formula 6: ammonium nitrate 100g / L, aminotriacetic acid 40g / L, hexamethylenetetramine 20g / L, pH = 6, room temperature, regression speed 1 / 5min, low cost.

Formula 7: sodium m-nitrobenzenesulfonate 110-130g / L, sodium cyanide 100-120g / L, sodium hydroxide 8-10g / L, trisodium citrate 20-30g / L, 80-90 ℃, suitable for the stripping of electroless nickel coating on precision steel parts.

Formula 8: sodium m-nitrobenzene sulfonate 100g / L, NaOH 100g / L, ethylenediamine 120ml / L, sodium dodecyl sulfate 0.1g/l, 60-80 ℃. Adding sodium m-nitrosulfonate during adjustment can make the regression speed recover to 80% of the maximum regression speed.

(2) Electrolytic stripping

The formula is: NaNO3 100g / L, aminotriacetic acid 15g / L, citric acid 20g / L, thiourea 2G / L, sodium gluconate 1g / L, sodium dodecyl sulfate 0.1g/l, pH = 4, room temperature, Da = 2 ~ 10A / DM2, cathode 10 × steel, SK ∶ SA = 23 ∶ 1.