GB/T 39807-2021Process specifications of Pb-free plating tin and tin alloys (English PDF)

3.1 Lead-free tin plating and tin alloy Pb-freeplatingtinandtinaloys

Lead-free tin electroplating and tin alloy plating.

3.2 Electroplating pure tin

Electroplated tin coatings with carbon content lower than 0.05% and tin content higher than 99.95%.

3.3 Electroplatingtin-copper

A tin-copper alloy coating with a copper content of 2% to 4%.

4.1 Process flow

4.1.1 Pre-treatment of electroplating

The electroplating pretreatment adopts a combination of chemical degreasing, cathode electrolytic degreasing, anode electrolytic degreasing and activation.

4.1.2 Electroplating underplating (optional)

When there are any of the following reasons, some substrate surfaces may require underplating.

a) Proliferation prevention (should be in accordance with C.2.2 and C.2.3 of GB/T 12599-2002);

b) Maintain solderability (according to C.2.2, C.2.3 and C.2.4 in GB/T 12599-2002);

c) Ensure the adhesion strength (should be in accordance with C.2.4 and C.2.5 in GB/T 12599-2002);

d) Improve corrosion resistance.

In order to avoid undesirable properties, such as brittleness, to the base material or processed parts, attention should be paid to the choice of the underlying coating. For example, should be avoided Use high-stress nickel plating.

If the base material is a zinc-containing copper alloy and solderability is required, in addition to the specified tin plating thickness (should be in accordance with GB/T 12599- C.2.3) in 2002, it is also necessary to make the minimum local thickness of the nickel or copper underplating layer reach 2.5µm; this underplating layer is important for maintaining a good outer layer. View and adhesion strength are also necessary.

If the bottom coating has been determined, the buyer should specify its characteristics (should be in accordance with GB/T 12599-2002 Appendix C) and minimum local thickness (Should be in accordance with 10.2 of GB/T 12599-2002).

The thickness of one or more bottom coatings should be measured in accordance with the method specified in Appendix A of GB/T 12599-2002.

4.1.3 Electroplating tin and tin alloy

Electroplating tin and tin alloy can use sulfate or methane sulfonate process, and appropriate additives should be used to meet the requirements of this standard. The required coating.

4.1.4 Post-processing

In order to improve the discoloration resistance and high temperature resistance of the coating, a suitable treatment solution should be used for post-treatment.

The water, raw and auxiliary materials used in lead-free tin electroplating and tin alloy processes should be lead-free.

4.2 Production Control

4.2.1 Inspection of production equipment

Before production, the operator should check whether the relevant production equipment has a qualified label or certificate, and it can be used within the validity period after verification.

4.2.2 Water quality requirements

Preparation of electroplating tin and tin alloy and post-treatment liquid, all washing after electroplating should use deionized water or distilled water.

4.2.3 Washing

In the production process, two or more water washings are carried out after each process to ensure that it is cleaned.

4.2.4 Bath analysis

All bath components should be analyzed regularly, and not less than three times a week, and the impurities in the plating solution should be analyzed once a week with complete records.

4.2.5 Filter

Continuous filtration should be used in the electroplating process, and the circulation of bath liquid should not be less than four times per hour, and the record should be complete.

4.2.6 Freezing

Electroplating tin and tin alloy solutions are prone to hydrolysis of divalent tin due to high temperatures. The plating solution should be equipped with refrigeration equipment.

4.2.7 Production records

During the production process, the processing date, name, quantity, time, current and addition of raw and auxiliary materials should be recorded.

4.3 Alternative samples

When parts are not suitable for destructive testing, samples can be used instead of parts, the test piece is 150mm×100mm×1mm copper plate, The test piece should be electroplated and other treatments under the same conditions as the represented parts.

4.4 Equipment requirements

4.4.1 Power requirements

The power supply used for electroplating can adopt various DC power supplies, and the rated output value of voltage and current should be able to meet the minimum requirements of the plating tank under full load.

Large voltage and current. The accuracy grade of the voltage and ammeter should not be lower than 1.5.

4.4.2 Slot requirements

The tank should have corrosion resistance to the solution contained, and the tank should be equipped with a ventilation device for electrolytic degreasing, acid activation, electroplating, etc.

4.4.3 Instruments and meters

Measuring instruments, meters, and measuring tools should have certificates of conformity and be regularly calibrated before they can be used within the validity period.

5.1 Substrate requirements

Lead-free tin electroplating and tin alloy substrates should meet the following requirements.

a) There should be no serious oil stains, metal chips, paint, rust and oxide scale, etc.;

b) The surface of the parts should be free of burrs, cracks, pits and other man-made damage caused by poor operation, and the surface is scratched;

c) The welded parts should be free of solder residue and slag;

d) Castings must not have unremoved sand particles and paint sintered products.

5.2 Coating copper and tin content

Use stainless steel as the substrate for electroplating tin or tin alloy, use 1.1 nitric acid to remove the surface coating, and use atomic absorption spectroscopy (or other instruments) to measure The amount of tin, lead and copper content, the coating should be lead-free, the copper content of electroplated tin-copper alloy is 2% to 4%, and the tin content of electroplated pure tin coating is greater than 99.95%.

The electronic energy spectrum can also be used for direct measurement.

5.3 Appearance of the coating

All parts should be visually inspected. The coating is silver-white or slightly yellowish, and the coating crystals are uniform, fine and smooth. hang Plated parts allow slight fixture marks on hidden parts. Allows slight unevenness due to uneven substrate material and different surface processing conditions Uniform color or gloss; the surface of the parts after high temperature inspection is allowed to slightly turn yellow. Spots, black spots, burnt, roughness, pinholes, and hemp are not allowed Spots, cracks, delamination, blistering, peeling, peeling, crystalline coating, partial non-coating (except for blind holes, deep holes and technical documents), etc. defect.

5.4 Coating thickness

Pure tin and tin alloy coatings are classified according to thickness, and are used for different conditions of use in accordance with 7.1 of GB/T 12599-2002. The minimum thickness value is specified in Table 1.

According to the appropriate method given in Appendix A of GB/T 12599-2002, any small diameter of 20mm can be measured in the main surface.

A basic measuring surface on the part contacted by the ball shall be measured in accordance with GB/T 12334 for the thickness of the coating. When the main surface area of the plated part When it is greater than or equal to 100mm², the minimum thickness shall be regarded as the minimum local thickness value. When the main surface of the plated part is less than 100mm², the minimum The thickness should be regarded as the minimum value of the average thickness.

5.5 Bond strength

When the buyer stipulates that the test should be carried out according to one of the methods given in Appendix B of GB/T 12599-2002, the coating should not peel off phenomenon.

5.6 Solderability

5.6.1 General materials and parts

If the purchaser has regulations on solderability, it should follow the method 1 of the Ta test in GB/T 2423.28, and use inactive flux for solderability. test.

If accelerated aging is required before the test, the purchaser shall specify the accelerated aging process.

5.6.2 Printed Circuit Board

If the buyer has regulations on solderability, the plating on the printed circuit board that meets this standard should be tested in accordance with the Tc test method in GB/T 2423.28 Method for solderability test.

If accelerated aging is required before the test, the purchaser shall specify the accelerated aging process.

5.7 Porosity

If the purchaser has regulations on porosity, for coatings with a minimum thickness greater than or equal to 10 µm, one of the following tests should be passed.

a) The coating on the steel substrate is in accordance with the provisions of GB/T 10125;

b) The coating on non-steel substrates shall be in accordance with GB/T 9789.

In the above two cases, when observed with a three-fold magnifying glass, the substrate should have no traces of corrosion.

5.8 Anti-tarnish performance

In a closed container, heat pure water (conductivity less than 5µS/cm) to 100°C under normal pressure, place the work piece 1cm on the water surface, and expose it to steam.

After 5h in the steam, the coating does not change color.

5.9 Anti-tin whisker performance

Use a high and low temperature damp heat test chamber at a temperature of 85°C and a relative humidity of 85% to carry out the experiment for 1000 hours, and then use the scanning electron microscope to zoom in Observed at.200 times, there should be no whiskers.