PCB Technical - Defects of pure tin plating on PCB

In the production process of circuit board, most manufacturers still use wet film process imaging due to cost considerations, which will inevitably cause the troubles of "plating, bright edge (tin thin)" and other adverse problems when graphics are plated pure tin. In view of this, I will summarize the solutions to common problems of pure tin plating process over the years and discuss them with you. Among them, the electroplating process of circuit board can be divided into acidic bright copper electroplating, nickel/gold electroplating, tin electroplating. The article introduces the technology and process of electroplating process, as well as the specific operation method.

PCB Technological process:

Acid immersion copper plating on the whole plate graphic transfer acid deoiling acid deoiling acid deoiling acid reflux washwash micro etch second countercurrent washwash acid immersion second countercurrent washwash 8594;countercurrent wash 8594;acid 8594;graphic platplatplating copper second countercurrent washwash nicnicnickelplating second water wash citric acid 8594; gold plating gold plating recovery gold plating Class 2-3 Pure Washing Drying

2. Cause analysis of "plating by osmosis" on wet diaphragm (quality problem of non-pure tin medicine)

1. The copper surface polished by brushing before printing must be clean to ensure good adhesion between the copper surface and the wet oil film.

2. Low exposure energy of wet film will result in incomplete light curing of wet film and poor resistance to electroplating pure tin.

3.The parameters of wet film pre-baking are unreasonable and the local temperature of the oven varies greatly. Because the thermal curing process of photosensitive materials is sensitive to temperature, low temperature may lead to incomplete thermal curing, which reduces the resistance of wet film to electroplating pure tin.

4. Failure to post/solidify reduces the resistance to electroplating pure tin.

5. Wash the plates out of pure tin plating thoroughly and thoroughly. At the same time, every plate compartment socket or dry board should be used. No overlapping is allowed.

6.Quality of wet film.

7. The impact of production and storage environment and time. Poor storage conditions or prolonged storage time will expand the wet film and reduce its resistance to electroplating pure tin.

8. The wet film is dissolved by pure tin luminant and other organic contamination in the tin cylinder. When the anode area of the tin plating trough is insufficient, the current efficiency will inevitably be reduced. Oxygen evolution occurs during the electroplating process (electroplating principle: anode oxygen evolution, cathode hydrogen evolution). If the current density is too high and the sulfuric acid content is too high, hydrogen evolution from the cathode will attack the wet film and lead to tin leaching (i.e.'plating').

9. High concentration (sodium hydroxide solution), high temperature or long soaking time of the defilm solution will produce tin flow or tin dissolution (i.e.'plating').

10. The current density of pure tin plating is too high. Generally, the mass current density of wet film is between 1.0 and 2.0A/dm2, which exceeds the current density range. Some wet film quality is prone to "seepage plating".

3. Causes and Improvement Measures of "Penetration" Caused by Drug-water Problem

1. Reason:

Drug-water problem leads to "plating" mainly depending on the formula of pure tin gloss agent. Light agent penetration is strong and "plating" occurs during the process of plating against the wet film. That is, "plating" occurs when too much pure tin light agent is added or the current is slightly larger. Under normal current operation, the resulting "plating" is related to the uncontrolled operation conditions of medicinal water, such as excessive pure tin light agent, high current, tin sulfate or high sulfuric acid content, which will accelerate the attack on the wet film.

2. Improvement measures:

The performance of most pure tin luminaires determines that they are more aggressive to wet film under the action of current. To avoid the "plating" of wet film plated pure tin plate, three points are recommended for normal production of wet film plated pure tin plate:

1. The addition of pure tin luminant must be monitored in a small number of ways. The lower limit of the content of pure tin luminant in plating solution is usually controlled.

2. The current density is controlled within the allowable range.

3. Drug composition control, such as tin sulfate and sulfuric acid content control in the lower limit will also be beneficial to improve the "plating".

CHARACTERISTICS OF MARKET PURE TIN LIGHT AGENTS

1. Some pure tin luminaires are limited to current density and have a narrow operating range. This kind of pure tin luminaire is usually prone to wet film "plating". It has a narrow allowable standard range for operating condition parameter control in relation to stannous sulfate, sulfuric acid and current density.

2. Some pure tin luminaires are suitable for a wide range of current density operations. This kind of pure tin luminaire is usually not easy to produce wet film "plating". It has a wide allowable standard range for operating condition parameter control in relation to tin sulfate, sulfuric acid and current density.

3. Some pure tin luminants are prone to "leak plating, leak plating, blackening" or even "shining" of the line edges on the wet film;

4. Some pure tin luminants do not cause "shining" of the line edges of the wet film (no baking plate or no UV curing treatment), but there are still "plating" problems sometimes, which can be improved by baking plate or UV curing treatment. Before the wet film plating process of pure tin, there were no problems such as "shine, plating" on the line edge without baking plate or UV curing treatment. At present, there are few such pure tin luminants on the market.

The operation should strictly control the operating current density, temperature, anode area, tin sulfate, sulfuric acid and the content of tin light agent according to the characteristics of pure tin light agent provided by different pharmaceutical water suppliers.

5. Reasons for "shiny" line edges caused by pure tin plating on wet diaphragm plates

Because the pure tin luminant formula generally contains organic solvents, while the wet oil film itself consists of materials such as organic solvents, the two are incompatible, especially reflected in the "shine" at the edge of the line.

Factors associated with the "shine" of line edges:

1. Pure tin luminescent agent (usually containing organic solvents in the formula);

2. Low current density (the lower the current density, the easier the line edge "shine");

3. The conditions of the grilling plates do not match (the main purpose of the grilling plates is to evaporate organic solvents from the wet oil film);

4. Ineven thickness of the wet film on screen printing (the thicker the film, the easier it is to "shine");

5. The quality problem of the wet oil film itself (select the wet oil film to match the electroplated pure tin medicine);

6. The quality of acidic degreaser after pre-treatment (the selected acidic degreaser enhances the washability of the solution and greatly reduces the residual probability on the copper surface after degreasing);

7. Excess tin gloss agent in the plating solution (excessive tin gloss agent will cause organic pollution of the plating solution, to prevent contamination of tin cylinder by wet film tinplate with increasing capacity, 8 hours carbon core filtration is carried out every half month, and 5 hours, 2.5 hours and 0.5 hours are electrolyzed with current densities of 5ASF, 10ASF and 15ASF each week);

8. Temperature is related (the higher the temperature, the more uneven the position of the low potential zone, the higher the temperature, the easier the "shine" of the line edge. In addition, the higher the temperature, the faster the oxidation of Sn2+ and the consumption of additives.)

9. Bad conduction (Bad conduction directly results in a serious low current density, which is easy to "shine" at the line edge when the current density is less than 10ASF).

10. Storage time of wet film sheet is long (wet film plated pure tin sheet should be stored in relatively good environment workshop, storage time should not exceed 72 hours, staff in graphic electroplating process take sheet according to production condition, but storage time in electroplating shop should not exceed 12 hours);

11.Insufficient area of anode in tin-plated trough (insufficient area of anode in tin-plated trough will inevitably lead to lower current efficiency and oxygen evolution during electroplating. The area ratio of anode to cathode is usually 2-3:1, and the standard interval between anodes in tin-plated trough is about 5 cm, in order to ensure adequate area of anode).

Therefore, some bad problems are actually caused by the unimportant details of an operation, so long as many aspects are considered, the key to the problem can be found and solved.

6. Advantages and disadvantages of market quality of wet film

Good wet film quality is beneficial to reduce the "shine" of line edges, but it cannot be completely eliminated. In addition, the oil film suitable for pure tin plate is not necessarily good. Here is a brief description of the quality characteristics of the wet film:

1. Good wet film is not easy to produce "plating". Oil film is not easy to break down and easy to remove when current density is high.

2. Some wet film may play a role in reducing the "shine" problem of line edges, but it is relatively difficult to remove the film. This kind of wet oil film is not suitable for medicines with a wide range of current density operation. Slightly higher current density may lead to problems such as "plating, clamping, blackening" and even breaking through the oil film.

About Tin Electroplating

Purpose and function: Graphic electroplating of pure tin mainly uses pure tin as a metal anti-corrosion layer to protect the line from etching.

(2) The fluids consist mainly of tin sulfate, sulfuric acid and additives; The content of tin sulfate is controlled at about 35 g/l and the sulfuric acid is controlled at about 10%. The addition of tin-plating additives is generally supplemented by the method of kilo-an-hour or according to the actual effect of the production board. The current calculation for tin plating is generally 1. 5A/Square decimeter multiplied by the electroplatable area on the board; Tin cylinder temperature is maintained at room temperature, generally not more than 30 degrees, mostly controlled at 22 degrees. Therefore, in summer because the temperature is too high, it is recommended to add a cooling temperature control system to the tin cylinder.

(3) Process maintenance: timely supplementation of tin plating additives per kilo-an hour per day; Check if the filter pump is working properly and there is no air leakage. Clean the cathode conductive rod with a clean damp cloth every 2-3 hours. Periodically analyze tin sulfite (once a week) and sulfuric acid (once a week) in tin pots every week, and adjust the content of tin plating additives through Hall slot test, and timely supplement of relevant raw materials; Clean the anode conductive rod and the connectors at both ends of the groove body every week. Use low current 0 per week. 2? 0. 5ASD electrolysis 6? 8 hours; Every month, the anode bag should be checked for damage, and the damaged should be replaced in time. Check if any anode mud is accumulated at the bottom of the bag and clean it in time if necessary. Continuous 6 monthly filters with carbon cartridge? 8 hours with low current to remove impurities; The need for large treatment (activated carbon powder) is determined according to the contamination status of the fluids around half a year. Replace the filter cartridge of the filter pump every two weeks;

(4) Processing procedure: A. Remove the anode, remove the anode bag, wash the surface of the anode with a copper brush, wash and dry it, put it in the anode bag, put it in the acid tank for replacement B. Soak the anode bag in 10% alkali solution for 6? 8 hours, wash and rinse dry, then soak in 5% dilute sulfuric acid, wash and rinse for later use; C. Transfer the fluids to the spare slot, press 3? 5g/l slowly dissolve the activated carbon powder into the trough. After thoroughly dissolve, adsorb for 4-6 hours, use 10um P P filter cartridge plus filter powder filter trough liquid to clean the trough, put in the anode, hang in the electrolyte plate, press 0. 2-0. 5ASD Current Density Low Current Electrolysis 6? After 8 hours, D. After laboratory analysis, the contents of sulfuric acid and tin sulfate in the tank were adjusted to normal operation range. Tin plating additives are added according to the Hall groove test results. E. Stop electrolysis when the color of the electrolytic plate is uniform. F. Trial plating OK.

(5) When supplementing medicines, such as tin sulfate or sulfuric acid, when a large amount is added; Low current electrolysis should be done after adding; Safety should be paid attention to when adding sulfuric acid. When the amount of sulfuric acid is large (more than 10 liters), it should be added slowly several times. Otherwise, it will cause excessive temperature of the groove liquid, oxidation of tin oxide, and accelerate the aging of the groove liquid.

Formula for calculation of drug addition:

Tin Sulfate (in kilograms) = (40-X) * Slot Volume (L)/1000

Sulfuric acid (unit: liter) = (10%-X) g/L * Slot volume (liter)

Or (in liters) = (180-X) g/L * Slot Volume (L)/1840