King Sun PCB

Gold finger PCB design purpose: through the connector plug as the board of external contacts output, so gold finger process is needed.

The characteristics of gold: it has superior conductivity, wear resistance, oxidation resistance and reduce contact resistance. But gold is very expensive, so it is only used for partial gold plating or chemical gold of gold fingers, such as bonding pad and so on.

The process flow

Upper panel—>grinding panel (micro corrosion)—>washing—>activating—>washing—>nickel plating—>washing—>activating—>washing—>gold plating—>gold recovering—> washing—>drying—>laying down

A.Steps:

Tape sticking—>Reel tape—>Automatic nickel gold—>Tear tape—>Washing and drying

The role of auxiliary components in plating bath

• Boric acid: buffer function, can maintain the relative balance of pH value, the concentration of 35~55g/l; nickel chloride: is an anode activator, can effectively promote the dissolution of the anode nickel angle, to avoid passivation of the anode.
• Brightener: can improve the brightness of the coating, the brightener used for ACR-3010, the control range is 25~35ml/l.
• Anti pinhole agent: can effectively remove the hydrogen bubble on the coating to prevent pinhole defects.
• Brightener and anti – pinhole additive method: less frequently used, plus appropriate, one-time do not add too much.

B.Homework and precautions

1.The purpose of adhesive tape

• The board is only exposed to the part of the gold-plated finger, and the other is covered with adhesive tape, anti plating. Tape is a tape Sumikin deliberately, finger and finger too far away from the phenomenon is not allowed to prevent cuts in the removal of the tape sheet, avoid man-made scratch.
• Operation should pay attention to the use of tape can not be “degumming” phenomenon, so as to avoid residual copper stains. This step is the most human consumption, and the listing of automatic taping machines will bring another revolution in industry.
• The purpose is through the tape reel, the tape reel machine and plate compact, avoid the tape is not compacted in nickel gold tape inside drops caused cross contamination between the cylinder drops.

2.Grinding panel (micro corrosion)

Remove the grease, oxide and green oil on the surface of the panel, provide a bright, rough copper surface, and increase the bonding power between the copper layer and the nickel plated layer.

3.The role of activation

Removal of copper surface, slight oxidation of the skin and copper surface re oxidation, so that the copper surface more polished clean, to maintain the copper layer or nickel layer of activity, and enhance the substrate metal and metal to be plated between the bonding force.

4.Plating with nickel

As the gold layer between the copper layer and the barrier to prevent copper migration. to improve production rate and save the amount of gold, now almost all of the vertical conveyor belt automatic Au plating equipment, main salt bath is a nickel sulfamate nickel content is very high and very low stress of coating (Nickel Sulfamate Ni (NH₂SO₃)2_o 4H₂O).

C.Analysis of gold finger common problems

1.High current zone burning

Reasons: the concentration of gold is not enough; the proportion is too low; the mixing is not enough; the gold plating liquid is contaminated by nickel and copper.

Processing method: adding salt; high proportion; strengthen stirring; removal of metal pollution.

2.Coating adhesion is not good

Reasons: poor bonding of copper and nickel; bad combination of nickel and gold; poor cleaning before nickel plating; great stress on nickel plated layer.

Processing method: pay attention to the effect of copper treatment before nickel plating; pay attention to the effect of nickel treatment before gilding; strengthen the effect of pre plating treatment; clean plating solution; carry out cylinder or carbon treatment on nickel cylinder.

3.Gold color is bad

The reason is that the additives are too small, the pH is too high, and the plating solution is contaminated by Ni2+ and other metal ions.

Treatment methods: supplement the right amount of additives, adjust the pH value, remove metal pollution, and pay attention to the prevention of pollution at ordinary times, especially the frequent occurrence of nickel ion pollution.

4.Board gold color (face color bad, especially in the wet season)

Reasons: cleaning and drying are not complete; gold-plated plates are stored in corrosive environments.

Treatment method: strengthen the cleaning and drying effect after gilding; gold-plated plate should be kept away from corrosive environment.

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