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PCB Blog - Common problems and improvement methods of ENIG PCB

PCB Blog

PCB Blog - Common problems and improvement methods of ENIG PCB

Common problems and improvement methods of ENIG PCB

2022-10-09
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Author:iPCB

1. ENIG plating NG

Cause analysis of the problem:

1.1 Nickel cylinder is too active; 2. High concentration or contamination of activated palladium by pretreatment (iron, copper ion contamination or high local temperature accelerates ageing of liquid medicine), long time of immersion plate, high temperature or insufficient washing after activation cylinder (i.e. before nickel deposit); 3. The grinding plates in the previous operation are too deep to absorb palladium, the rollers on the equipment are not thoroughly cleaned before the grinding plates, and the water pressure is insufficient to flush the remaining copper powder on the edge of the line (not completely etched away), and the residual copper and nickel deposits after etching are prone to seepage plating. 4. High concentration of colloid-activated palladium was obtained after PTH pretreatment.

Corresponding improvement measures:

1.2 Strictly control the nickel cylinder load from 0.3 to 0.8 dm2/L and appropriate stabilizer, revert the cylinder when the anode protection current is > 0.8A; 2. Strictly control the concentration of the activated tank liquid, the immersion time, the working temperature, the washing time, the fully washed plate after activation and try to avoid the pollution of the tank liquid; 3. QC boards before nickelization should be inspected and etched to ensure no residual copper, clean brush equipment, Micro-etching depth, abrasive board depth and water pressure must be sufficient (1000-1500''for ordinary soft board brushing and 800-1000'for hard board brushing, now brushers are often used to maintain consistent appearance and quality); 4. The concentration of colloid-activated palladium in the pretreatment of copper carbide PTH should be properly controlled.


2. Leakage plating of ENIG

Cause analysis of the problem:

2.1.Activated palladium concentration is too low, immersion activation time, insufficient temperature, activated contamination or plate left in sink too long before nickel deposition (passivation); 2. Copper surface is contaminated by residual glue or dirty treatment (tin removal, external contamination or previous process contamination); 3. Excessive amount of Chinese medicine water stabilizer in nickel sink, low temperature, inadequate activity (dark nickel layer, dark red gold color on the surface after gold sinking), insufficient load, metal or organic pollution or stirring too intense are prone to "leak plating". The copper surface is badly oxidized or poorly washed after development. The PH of nickel groove and the copper surface are contaminated by sulfide or improperly added.

Corresponding improvement measures:

2.1. Controlling the concentration of palladium in the activated fluids, the immersion time, the working temperature, reducing the contamination of copper ions (to be replaced when the activated copper ions are larger than 100PPM), and ensuring that the plates remain in the sink for too long before nickel sinking; 2. Make sure that there is no residue on the copper surface of the plate and that the copper surface is cleanly treated when nickelizing is pretreated; 3. Controlling the operation parameters of nickel reduction groove, ensuring the pre-nickelization activity, increasing auxiliary copper plate in the groove to increase load, avoiding metal or organic pollution, and controlling stirring properly should not be too intense.

ENIG Immersion Gold PCB

3. ENIG Immersion Gold PCB nickel layer "whitening" (nickel layer sub-layer, nickel layer thickness is insufficient)

Cause analysis of the problem:

Nickel slot metal nickel ion is too low or too high, temperature is low, PH value is low, activity is insufficient, time is insufficient, load is large, phosphorus content is high (line or hole edge is white) or nickel bath liquid < or > 4MTO.

Corresponding improvement measures:

When nickel ion is adjusted to a range, temperature control, PH value, activity improvement, load reduction, phosphorus consumption reduction to the allowable range value or nickel reaches or exceeds 4MTO, the test should be strengthened and replaced according to the quality requirements.


4. Coarse and white ENIG PCB layer

Cause analysis of the problem:

4.1.Residual glue or medicinal liquid on the copper surface of the incoming material, dirty or rough copper surface itself, serious oxidation of the copper surface, excessive micro-etching, high (uneven) Micro-etching of copper ions, and unclean tin removal; 2. Gold trough contamination (contamination by nickel metal impurities) or imbalance (excessive or small load), low temperature, low PH value, low gold concentration, low specific gravity, too many stabilizers (complexes), insufficient gold layer thickness or gold trough medicinal water up to 4MTO or above; 3. Poor nickel deposit itself (thin nickel layer or negative-positive color), such as dark appearance of the gold layer after gold deposit, mainly the dark nickel layer, poor nickel bath liquid activity (unstable), excessive local speed of nickel cylinder circulation, local overheating of nickel cylinder temperature or excessive concentration of nickel stabilizer; 4. Solid particles, whitening or shedding of welding resistance (insufficient exposure or insufficient roasting time) in chemical nickel solution cause minor contamination of nickel-gold potions, palladium or copper; 5.Nickel trough plating solution PH is too high or the water quality is not clean.

Corresponding improvement measures:

4.1. Enhance inspection of incoming materials, quality of electroplated copper or select high-quality plates, control the rate of Micro-etching biting of copper, and remove tin clean (the copper surface of the plate before nickelization must be clean); 2. The components of the gold bath liquid must be controlled within the range. 3. Improve the quality of nickel deposit (grasp the control of activity/MTO and other components), ensure that the nickel trough circulating filtration and temperature of the trough liquid reach uniformity, and control nickel stabilizer within range; 4. Strengthen the filtration of chemical nickel solution and avoid contamination by impurities such as palladium or copper ions; 5. Make sure the water quality and the pH value of the nickel trough are kept within range.


5. Gold Layer "Drop Gold, Drop Nickel Gold" (Copper-Nickel or Nickel has poor binding with Gold PCB)

Cause analysis of the problem:

5.1. Passivation of nickel surface after nickel cylinder (before gold sinking), darkening of nickel layer, excessive nickel content of more than 5% added at one time, unbalance of accelerator in nickel cylinder, easily shake off nickel due to high phosphorus and nickel hole or line whitening, contamination of copper ions in nickel liquid or control of various parameters are out of range, etc. 2. The dirty (oxidized) copper surface, long wash-in time after development/microetching/activation or passivation of palladium layer surface after pretreatment activation, excessive activation or excessive concentration of palladium layer surface, inadequate wash-in with activation, poor oil removal or microetching effect, contaminated by copper ions in the activating solution or long stay time during non-working make the activation less active and lead to poor copper-nickel binding force; 3. The wash between the nickel cylinder and the gold slot is not clean or takes a long time, the pH value of the gold liquid is low (the gold layer is easy to corrode), the gold liquid is contaminated by metal or organic impurities (copper, iron, nickel, green paint, etc.), the gold depositing system is aggressive to the nickel layer (the nickel layer surface is blackened) or the composition control is out of range, etc.

Corresponding improvement measures:

5.1.Prevent the passivation of nickel surface, check the quality of nickel layer, add small amount of nickel in multiple ways or select automatic adder equipment to control (the maximum nickel content should not exceed 15% in the slot liquid each time, should be supplemented in stages when the amount of nickel is over 15%), adjust the accelerator in the nickel liquid, reduce the phosphorus content by consuming or diluting the slot liquid, minimize the pollution of nickel liquid by copper ions, and control the parameters of nickel within the range; 2. Enhance the cleanliness of the treatment plate in front of the copper and prevent passivation of the palladium layer surface after copper activation (long time in air or water), control the activation time or concentration, fully wash with activated water, improve oil removal or microetching effect (e.g. microetching with hydrogen peroxide + sulfuric acid + stabilizer series, excessive stabilizer will directly cause nickel-gold shaking), reduce or avoid copper ion pollution activation or excessive retention time, adjust or replace as appropriate; 3. Strengthen the washing of the gold sinking plates thoroughly, adjust the pH value within the range, detect the contamination degree of the medicinal water by impurities, select an appropriate gold sinking system to meet the quality and ensure that the parameters of each component are kept within the range.


6. Immersion Gold surface PCB "poor weldability" (solderability)

Cause analysis of the problem:

6.1. Gold is too thin; 2. The water quality is too poor (the effect of washing the gold plate is not good), the nickel or gold cylinder exceeds 4MTO, contamination of impurities, inadequate activity, black disc, nickel appearance is abnormal (whitening, dim); 3. Pre-treatment Micro-etching (high copper ion, selected hydrogen peroxide series, such as excessive detergent washing or long retention time) and activation (copper ion contamination/over-activation); 4. The content of nickel and phosphorus should not be less than 7% (preferably not more than 12%) and the compactness and deposition rate of nickel-gold layer should be well controlled (6-8 u/min). 5. Gold deposit time is long, gold concentration is low, temperature is low or contaminated by organic or metal impurities.

Corresponding improvement measures:

6.1. The optimum thickness of gold is 0.05-0.1 μ M; 2. The gold-deposited plates need to be recycled washed with pure water overflow washed with pure hot water. Enhance maintenance to minimize activation, aging of nickel or trough medication, avoid pollution, enhance activity, eliminate black disc problems (black disc corrodes heavily on the chemical nickel layer with P content in acidic bath, easily produces P-rich layer which leads to decreased solderability, while the high free energy of nickel and nickel is more prone to oxidation than other crystal boundaries, reaching a certain degree of gray to black oxidation layer) and enhance the appearance quality of nickel layer; 3. Strengthen the control of pre-treatment microetching and activation parameters; 4. Controlling the phosphorus content from 7 to 9% (medium phosphorus) and the nickel deposition rate; 5. Increase the gold concentration or temperature to reduce the gold sinking time (within 10 minutes), reduce the contamination of the medicinal water in the gold trough, or replace the gold according to the contamination level.


7. Corrosion of nickel layer (black disc)

Cause analysis of the problem:

7.1. Long time to sink gold; 2. The pH value of the gold trough liquid is too low, the temperature is low and the gold concentration is low. 3. Potential difference caused by uneven distribution of nickel and phosphorus; 4. It is difficult or too slow to get gold when the water is aging or contaminated by impurities; 5. Gold deposit system is highly aggressive against nickel layer. 6. The nickel layer is too thin (less than 2) μ M); 7. Failure to thoroughly clean the nitric acid residue when inverting the nickel slot will lead to corrosion of the deposited nickel layer. 8. Keep corrosive workshops for a long time; 9. The high P H of the nickel slot results in the low P content of the nickel layer and the reduced corrosion resistance of the nickel layer.

Corresponding improvement measures:

7.1. Control the rate and time of gold deposition and control the thickness from 0.05 to 0.1 μ M is suitable, it is not recommended to exceed 8u;; 2. Control the pH value, temperature and concentration of the gold trough liquid to a range; 3. Improve the nickel slot without strong air stirring under the heating tube, and make the nickel-phosphorus distribution more even by appropriate swing, vibration, filtration or air stirring; 4. Increase the gold concentration or replace it if necessary depending on the degree of contamination; 5. Select high-quality gold system products with little attack on nickel layer; 6. Control the thickness of nickel layer from 3 to 4 μ M; 7. Eliminate nitrate ion contamination of tank fluids; 8. The plates that come out of nickel-gold carbide need to be transferred to the next operation in time to avoid long-term placement. 9. Control the PH of the nickel slot within the range during production, try not to be higher than 4.8, especially at the end of the nickel slot.


8. Pinhole in nickel layer

Cause analysis of the problem:

8.1. Bad exhaust of nickel slot filter, bad nickel layer oscillation, and weak stirring of nickel slot; 2. Soluble particles in nickel plating solution, poor pretreatment or organic contamination of nickel trough solution (detergent/base material/green paint, etc.);

Corresponding improvement measures:

8.1. Improve the exhaust condition of the filter, leakage of circulating pipeline, low level of circulating suction inlet, maintain the exhaust parts of the oscillator and increase the intensity or frequency of oscillation, increase the mixing and swing speed (try out the best mixing conditions); 2. Strengthen the filtration of nickel tank liquid, improve the pretreatment and reduce the organic pollution of nickel tank liquid.


9. The current of the ejection protection device is too high (consumes a lot of nickel)

Cause analysis of the problem:

9.1. Nickel bath temperature is high, PH is high, local temperature is overheated, replenishment fluid is added too fast, tranquilizer is too low; 2. Slot wall passivation; 3. A small amount of activating liquid is carried in; 4. The nickel and gold fragments on the hanger fall into the nickel slot; 5. Abnormal ejection protection device; 6.Stainless steel groove body is not passivated properly.

Corresponding improvement measures:

9.1. Control the operating parameters of the liquid nickel; 2. Stop passivation of groove walls; 3. Avoid small amounts of pretreatment activation residue being carried into contaminated nickel liquids; 4. Regular inspection and removal of the deposits on the hanger are required; 5. Improve the anode release protection to ensure normal operation; 6. Re-passivation with nitric acid.


10. Liquid nickel "turbidity"

Cause analysis of the problem:

10.1. Nickel PH, high temperature; 2. Too much carry-out; 3. Drug or air leaks from pipes; 4. The imbalance activity is too high.

Corresponding improvement measures:

10.1. Keep the nickel PH value and temperature within the range; 2. Pay attention to the operation of employees (most of them choose automatic line devices); 3. Improve equipment; 4. Enhance the maintenance of the solution and ensure the normal activity of the nickel solution.