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Defects of pure tin in PCB electroplating process

Purpose and function:

The pattern is electroplated pure tin with the purpose of purely using pure tin as a metal resist layer to protect the line from etching;
The bath is composed of stannous sulfate, sulfuric acid and additives;
Stannous sulfate content is controlled at around 35 g / L, sulfuric acid is controlled at about 10%; add tin additives generally in accordance with the method of kiloampere hours to supplement or according to the actual production of tin plate effect; the current calculated by 1. 5 / square decimeter plate can be multiplied by the plating area; tin cylinder temperature maintained at room temperature, the temperature is generally not more than 30 degrees, more than the control at 22 degrees, so in the summer because the temperature is too high, the tin cylinder is recommended to install cooling temperature control system;
Process maintenance:
Remove the A. anode, remove the anode bag, with a brush to clean the surface of the anode copper, water rushed after dry, anode bag into the acid tank B. will spare anode bag into 10% alkaline soaking for 6? 8 hours, water rushed dry, then 5% dilute sulfuric acid soaking, washing washed dry standby; C. bath transferred to the reserve tank, at 3? 5 g / l will slowly dissolve into the activated carbon bath, to be completely dissolved after the adsorption of 4-6 when using 10um PP filter and filter powder filter tank liquid to clean the working groove, into the anode, hang into the electrolytic plate, press 0. 2-0. 5ASD low current density current 6? 8 hours of D., by analysis, adjustment in the groove of the sulfuric acid, stannous sulfate content to the normal operating range; according to Holzer cell test results of tin additives; E. electrolytic plate color uniformity, namely stop electrolysis; plating OK. is F.;
Five, when supplements:
Such as adding a large amount of such as stannous sulfate, sulfuric acid; adding after low current electrolysis; adding sulfuric acid should be Caution!, adding a large amount of time (10 liters) should be added slowly several times; otherwise it will cause the bath temperature is too high, stannous oxide, accelerate the aging of the bath;
Six. Formula of adding medicine:
Stannous sulfate (unit: kg) = (40-X) * trough volume (liters) /1000
Sulfuric acid (unit: liter) = (10%-X) g/L * trough volume (liters)
Or (unit: liter) = = (180-X) g/L * trough volume (L) /1840
In the process of making circuit board, the majority of manufacturers due to cost factors are still using the imaging process of wet film, it will cause the graph when they appear pure tin plating plating, bright side (TIN) "and other adverse problems, in view of this, I will solve the common problems of pure tin plating process for summary a, to discuss with you. Electroplating process of the circuit board, about classification: bright acid copper plating, electroless nickel / gold, tin plating, this paper is on the circuit board processing process, technology and process of plating process, and method of operation.
Technological process:
Pickling, full plate electroplating copper and pattern transfer to acidic degreasing, two stage countercurrent rinsing, micro etching, two stage countercurrent rinsing, pickling, tin plating, two stage countercurrent rinsing, countercurrent rinsing, pickling, electroplating copper and graphics two countercurrent rinsing, washing, soaking plating nickel and two citric acid, gold plated 2-3 grade and recovery, water washing and drying
Two. Analysis of the reasons for the "wet plating" produced by wet film
1., screen printing brush brush out of the copper surface must be clean, to ensure that the copper surface and wet oil film adhesion good.
2. wet film exposure, when the energy is low, will lead to incomplete solidification of wet film, and the ability to resist pure tin plating is poor.
3. the parameters of wet film pre baking are not reasonable, and the oven temperature varies greatly. Because the heat curing process of sensitive materials is sensitive to temperature, the low temperature leads to incomplete heat curing, thus reducing the resistance of the wet film to the pure tin plating ability.
4. without post / curing treatment, the plating resistance to pure tin is reduced.
A plate washing 5 tin plating out to completely clean, and shall each plate inserting frame or plate, are not allowed to pack.
6. quality problems of wet film.
7. production and storage environment and time impact. Poor storage environment or excessive storage time will expand the wet film and reduce its resistance to pure tin plating.
8 wet film is pure tin agent and other organic pollution in the tin tank of the attack when dissolved, the anode area will lead to the lack of tin slot current efficiency decreased, the oxygen evolution process of plating (electroplating principle: anodic and cathodic hydrogen). If the current density is too large, and the sulfuric acid content is high, the cathode hydrogen evolution attacks the wet film, which leads to the occurrence of tin penetration (that is called "plating").
9., the high concentration of liquid film (sodium hydroxide solution), high temperature or long soaking time, tin or tin will be dissolved (that is, "plating").
10. plating pure tin current density is too large, general wet film quality is best, current density suitable for 1.0~2.0A/dm2 between, beyond this current density range, and some wet film quality is easy to produce "infiltration plating"".
Three, liquid problems lead to "percolation plating" causes and improvement measures
1. reasons:
Water lead to the plating "production mainly depends on the formulation of pure tin. Light penetration ability, and in the process of electroplating in the wet film attack, "infiltration" plating". Pure tin agent is added too much or slightly larger current will appear "plating", in the current normal operation, the "plating" with the syrup operating conditions do not control, such as pure tin agent, too much current is too large, stannous sulfate or sulfate content is high, these are will speed up the attack on the wet film.
2., improvement measures:
Most of pure tin agent itself determines its performance in the current under the action of wet membrane attack is relatively large, in order to avoid reduction