Discussion on Electroless Nickel Gold Technology (3)

4. Post-Processing:

After the PCB is plated with gold, it should be cleaned as soon as possible, preferably with hot water, to ensure water-free printing and meet the customer’s appearance requirements. At the same time, try to avoid storing in an acidic environment to avoid redness on the gold surface. It is best to transfer the pad paper away.

Finally, the impact of hidden dangers on upstream process quality.

There is no major problem with the chemical nickel-gold process itself, mainly due to the whitening of the solder mask and the exposed copper. And these two are caused by the hidden danger of wet film process quality.

1. Welding. The quality damage of the solder mask ink is the decisive factor, but the general ink can also minimize the severity as long as the process parameters are well controlled.

Our company uses TARUM TT-9G ink for pre-forming gold plate. The ink quality is very hard, and there is no solder mask whitening when plated in nickel tank for 50mm. However, the Sun 4000-GF5 ink was used instead, and the solder mask whitening was 20 mil. After testing, it was found that the board was not printed with text, and the whitening degree was 15 mil. It was judged that there was a text baking board. Therefore, the post-baking parameter of the wet film was changed from 150 ℃ 45min is changed to 150℃ 40min; the text baking board reference board is changed from 150℃ 20min (single-sided text) to 140℃ 15min, the solder resist whitening after making the board is only about 8mil, which can be accepted. Explain that the non-chemical gold plate is suitable for the ink. When making the plate, the baking time should not be too long, to avoid the excessive aging of the ink baking, and the aging of the welding resistance when the gold is formed.

2. Star point dew copper: This is the most troublesome problem. The main reasons are the density of the plate during wet film development and the washing of the baking plate after development (to facilitate the emission of organic solvents and oil fume), ventilation and the degree of cleanliness in the oven.

Found this situation, serious backwashing, slightly brushing twice, prolonging the micro-etching time to solve, the most effective method is to improve from the wet film process.

Causes and solutions of common problems：

1. Color difference:

Reason:

①The nickel tank is polluted or the service life has expired, and the organic matter in the tank liquid has accumulated too much.

②There are too many nickel ions in the gold tank.

③The concentration of palladium in the activation tank is insufficient.

Solution:

① Change the nickel tank to eliminate the source of pollution.

② Analyze the nickel content of the gold tank, if it exceeds 0.5g/L, change the tank.

③ Properly increase the palladium concentration.

2. Rough Coating

Reason:

① The activity of the nickel tank is too strong.

② The filtering is not enough, and the vibration frequency amplitude of the board is not enough.

③ Poor pretreatment.

Solution:

① Appropriately reduce the temperature, concentration and pH value.

② To strengthen the filtration, it is best to use a 5µm filter element for frontier filtration. At the same time, the vibration frequency and amplitude of the board are strengthened to facilitate the removal of hydrogen attached to the board surface.

③ Strengthen the pretreatment, and check whether the copper surface is rough or not.

3. Exposed Copper:

Reason:

① Foreign matter on the reverse side.

② Wet film development is not clean and water is not clean.

③ Palladium adhesion is not enough.

④ Washing for too long after activation.

⑤ The nickel tank potion is out of balance.

Solution:

① Heavy brushing (tracking the source of foreign objects).

② Wet film process review and improvement.

③ Control the Cu2+ content of the degreasing tank (less than 7g/L).

④ Shorten the washing time (15SEC).

⑤ Strictly add according to the proportion, and adjust according to the test results.

4. Gold Peeling:

Reason:

① The nickel layer contains high phosphorus content.

② Nickel layer passivation.

Solution:

①Analyze the phosphorus content with AA, appropriately reduce the adding range of reducing agent, if not, change the tank.

② Avoid exposing the nickel layer to the air for too long.

5. Poor nickel and copper bonding (nickel/copper delamination):

Reason:

① Unclean copper surface

② Pretreatment failure

Solution:

① Strengthen the pretreatment

② The content of Cu+ in each tank of chemical solution before analysis, if it exceeds the standard, replace it.

(Cu2+<7g/L in degreasing tank, Cu2+<15g/L in micro-etching tank. Cu2+<0.3g/L in pickling tank)

Conclusion:

The quality control of chemical nickel-gold process is not an easy task, especially the potential quality hidden dangers (such as solderability) can only be found after scraping the customer, but as long as the standard operation is strictly followed, the probability of problems will be reduced.