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Introduction of production process of circuit board gold finger
  • Date:2020-10-29
1、 Production purpose
The purpose of gold finger design is to use the connector as the outlet for the external contact of the board. The reason why gold is selected is because of its superior conductivity, oxidation resistance and wear resistance. Due to the high cost of gold, it is only used in gold finger, local plating or chemical gold, such as bonding pad, etc.
2、 G / F process
Coating blue glue → rolling glue → loading plate → pickling (or micro etching) → water washing → grinding brush → water washing → DI water washing → nickel plating → water washing → DI water washing → gold plating → recovery → plate removal → glue tearing → plate washing.
3、 G / F plating process
1. Coating: stick to the outer part of g / F for anti plating.
2. Pickling (or micro etching): clean copper surface and remove oxide scale.
3. Grinding brush: use flying wing grinding roller to remove oxide scale and S / m, C / M residual film on copper surface, so as to provide a clean surface for nickel plating
Copper surface. The choice of material hardness and pressure of flying wing grinding roller plays a decisive role in the grinding effect
If the pressure is too high, it will cause g / F short and wear marks; if the pressure is too small, it will not be clean; if the pressure is too soft, it will make sharp corners
G / F will produce grinding wire.
4. Nickel plating: it is used as a barrier between the gold layer and the copper layer to prevent copper migration. In order to reduce the internal stress of the coating, it is adopted now
Nickel sulfamate with high nickel content and low internal stress in the coating is used.
A. Composition and function of nickel cylinder liquid medicine
a. Main salt: nickel sulfamate Ni (nh2so3) 2, providing electroplating Ni2 +, high nickel content, high current efficiency,
High deposition rate, low internal stress, high brightness, low nickel content, good dispersibility and covering ability.
b. Anode activator: nickel chloride, can reduce the anode potential, depolarize significantly, accelerate the dissolution of the anode, prevent corrosion
Anodic passivation.
c. PH buffer: boric acid, to stabilize the pH value of the solution, prevent hydroxide precipitation and decrease due to high pH value
Hydrogen evolution can improve the current efficiency.
d. Additive: ① gloss agent: mp-200 (SE), with the effect of refining grain, leveling coating and obtaining bright coating.
② Wetting agent: naw-4 can reduce the surface tension, reduce the internal stress of the coating and prevent pinholes.
B. The reaction mechanism is as follows
a. Cathode reaction: ni2e + 2e → Ni (main reaction → nickel plating)
7h + + 2e → H2 ↑ (side reaction)
b. Anodic reaction: ni-2e → Ni2 + (main reaction → anodic dissolution)
4OH -- 4e → 2H2O + O2 ↑ (side reaction)
5. Gold plating:
At present, our factory adopts a series of citric acid gold plating with insoluble anode, and the gold salt is regularly supplemented in the form of solution. The plating efficiency of gold plating is very low, about 30-40% of the new plating solution, and it is reduced to about 15% due to gradual aging and pollution, so the stirring and circulation of gold plating solution is very important.
A. Composition and function of Jincang liquid medicine
a. Main salt: potassium gold cyanide K [Au (CN) 2] is a white crystal, which is dissolved by hot water and fed into the gold tank;
b. Complexing agent: potassium cyanide and citrate can improve the anodic polarization and refine the grains;
c. Conductive salt: 7000 conductive salt, can improve the conductivity of the solution, improve the dispersion ability of the bath.
d. Additives: 7000 supplements: bright, leveling, refining coating, reduce internal stress.
7000F supplement: provide Fe component of plating bath, improve coating structure and hardness.
B. The reaction mechanism is as follows
Cathodic reaction: [Au (CN) 2] - + e → Au + 2cn - (main reaction → gold plating)
2H + + 2e → H2 ↑ (side reaction)
Anodic reaction: 40H -- 4e → 2H2O + O2 ↑ (non solution anode)
6. Gold recovery: can reduce the cost of electroplating.
4、 Electroplating equipment:
1.0-4m/min any adjustable horizontal plating line, which requires smooth operation, no plate turnover, plate dropping and cylinder collision.
2. The stable pressure or current control of the gold nickel tank fire bull is required to be stable with small jumping up and down.
3. The gold and nickel cylinder heating and filtering system is good, the water retaining effect of each cylinder connection part is good, and there is no water leakage and less drain.
5、 Common problems and improvement measures:
common problem
Possible causes
Solutions
G / F pinhole
A. Copper based pinhole
B. Insufficient wetting agent or brightener
C. Concentration imbalance of liquid medicine
D. The temperature is too low
E. The current (voltage) is too high
F. Insufficient mixing or circulation
G. Too many organic impurities
H. There are too many impurities such as iron and copper
A. Improving pretreatment of copper plating and g / F plating
B. Adjust according to Hull cell test
C. Analysis and adjustment
D. Raise the temperature to 50-60 ℃
E. Reduce the current (voltage) appropriately
F. Properly enhance the stirring or increase the circulation amount
G. Carbon core filtration or carbon treatment
H. Low current towing cylinder or carbon treatment
G/Fshort
A. Poor grinding
B. Pre process short
A. Reduce the pressure of grinding roller, increase water washing, change to softer grinding roller.
B. Check and repair the plate; find out the cause and improve in the corresponding process
G / F rough
A. The current (voltage) is too high
B. The copper surface of the former process is rough
A. Reduce the current (voltage) appropriately
B. Check board repair; find out the cause and improve
G / f gold surface oxidation
A. The pH value is too high
B. Recycled gold water is too dirty
C. The urn is too dirty
D. Not washed in time or not dried
A. Adjust pH value
B. Exchange for recycled gold water
C. Check and replace the filter element (net) of gold cylinder
D. Timely washing and drying
Throwing gold and nickel
A. Poor grinding
B. The water is not clean
C. Passivation of nickel surface
D. The current stops during electroplating
E. There are impurities left on g / F
A. Increase the pressure of grinding plate appropriately
B. Change or increase water washing
C. Open activation cylinder before gold plating
D. Maintenance equipment and lines
E. Check the plate for repair or increase the grinding pressure appropriately
Infiltration of gold
A. The corrosion plate is not clean
B. Excessive grinding plate pressure
C. Too high current of no lead thickening gold
A. Inspection and repair; improve the effect of corrosion plate
B. Reduce the grinding pressure properly
C. Turn down the current and speed
Golden bad
A. Insufficient light agent
B. The gold content is too low
C. Organic pollution
D. The content of nickel and copper in gold cylinder is too high
A. Adjusted according to Hull cell test
B. Analysis supplement
C. Strengthen filtration, nickel cylinder can be used for carbon treatment
D. Update
Burning board
A. The nickel content is too low
B. Insufficient light agent
C. Current

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