October 2016 Archives

This volume introduces testing methods unique to industrial gold and gold alloy plating.

(1)Nitric acid aeration test (porosity test)

In this test, you will measure porosity of gold and gold alloy plating on a metal or nonmetal substrate by exposing the sample in the nitric acid vapor.

(1)Testing method

Prepare an appropriate size desiccator made of glass. Add a moderate amount of nitric acid into the bottom of the desiccator. Rinse a sample with ethanol or benzine and dry it. Place the sample on the porcelain plate of the desiccator and cover it with the lid. Let it stand for one hour at 23℃. Remove the sample from the desiccator. Then, rinse the sample with water and dry it.

(2)Assessment

Observe corrosion points generated from a defect, such as a pinhole on the test surface. Convert it to the number of corrosion points per 1 cm². The calculated value is the porosity.

(2)Color fastness test by heating

In this test, you will measure color fastness of gold and gold alloy plating on a metal or nonmetal substrate by heating it in a furnace. However, this test is not compatible with gold or gold alloy plating of less than 3 µm over copper undercoat or on a copper or copper alloy substrate. In addition, the testing method for partially plated products will be determined and agreed between the parties concerned.

(1)Testing method

Heat up the furnace to 120 to 130℃. Place a sample in it and wait for one minute. Then, remove it from the furnace and allow the sample to cool down.

(2)Assessment

Visually inspect the test surfaces and check for any discoloration.

(3)Hydrogen sulfide test (corrosion resistance test)

In this test, you will measure corrosion resistance of gold and gold alloy plating on a metal or nonmetal substrate by placing a sample in the hydrogen sulfide atmosphere.

(1)Testing method

Perform this test using a dedicated test machine for hydrogen sulfide corrosion. This machine is comprised of a temperature/humidity control equipment, a test piece support equipment, a hydrogen sulfide cylinder, a hydrogen sulfide quantitative dilution equipment, a concentration control equipment, and an exhaust treatment equipment. The testing conditions are as shown in the following [Table].

[Table] Major test conditions

(2)Assessment

Evaluate the degree of corrosion by the rating number standard drawings.

This section of JIS defines gold and gold alloy plating with the thickness of at least 0.2 µm on a metal or nonmetal substrate, produced for engineering purposes, including electrical / electronic products, machinery and other functional components.

(1) Definition of terms

1. Gold plating

Soft gold plating refers to electroplating with its gold content being 99.9% or more.

2. Gold alloy plating

This refers to electroplating with its gold content being 58.8% or more but no more than 99.9%. This plating is harder compared to the gold plating described earlier.

3. Multi-layer gold or gold alloy plating

This refers to plating comprised of two or more layers with different gold content.

(2) Quality

Here are the assessment items for determining the quality of plating films.

1. Appearance

Check the quality of polish, radiance and color, along with imperfections as roughness, burnt parts or pits.

2. Plating thickness

The minimum plating thickness is classified as follows:

[Table] Classification by the minimum plating thickness

3. Gold content in plating

4. Porosity of plating

Nitric acid aeration test (explained in another volume)

5. Resistance to discoloration by heating

Applicable to thick plating (explained in another volume)

6. Corrosion resistance of plating (explained in another volume)

7. Plating adhesion

8. Solder wettability of plating

9. Residual salt on significant plating surfaces

10. Electrical properties of plating

11. Plating hardness

12. Abrasion resistance of plating

(3) Plating name

Plating names are described by the symbols shown in this table.

In the next volume, we will learn testing methods of nitric acid aeration test, color fastness test by heating, and hydrogen sulfide test for industrial gold and gold alloy plating.

(1)Description of the bond test methods

The test methods introduced here are available for measuring the adhesiveness of electroplating. Select an appropriate method according to the characteristics of plating films.

1)Cathode electrolysis test

Measure the adhesiveness of nickel/chrome plating on a steel substrate through electrolysis.

2)Push-out test

Create a hole (not a through-hole) from the back side of a plated surface. Use a stick to push it out. This method is for industrial chromium.

3)Ruled line test

Use a needle-like tool to scratch a sample surface. This test is appropriate for soft plating.

4)Grinding test (1.Grinding stone. 2. File)

Test the adhesion by grinding the plated surface using 1 and 2.

5)Chisel test

Insert a sharp chisel between the plated layer and substrate to measure the adhesiveness.

6)Thermal test (1. Heating test, 2. Thermal-shock test)

(To be described later.)

7)Barrel polishing test

Rotate the barrel with a steel ball and a plating sample in it. This method is not compatible with soft plating.

8)Peeling test (1. Tape test, 2. Solder test)

(To be described later.)

9)Tensile test

Apply a tensile stress to the sample until it fractures. Measure the adhesiveness by the degree of extensibility.

10)Bend test

(To be described later.)

11)Winding bend test

Wind a thin wire or a strip around the mandrel. (Mandrel test)

(2)Tape test

In this method, you will measure the adhesiveness by pasting an adhesive tape on a plated surface and peeling it off as quickly and hard as you can. It is suitable for relatively thin plating. This method is not appropriate for thick plating. You need to use tapes with the width of 12 to 19 mm defined in JIS Z 1522.
Before pasting a tape, leave a streak mark that reaches through the substrate as you draw a 2-mm square using a sharp knife to make the assessment more accurate.

(3)Bend test

This test measures the plating adhesiveness by bending a test sample. Use stakes with the bending radius of between 4 and 10 mm to secure the sample onto a vise. Repeat the process of bending the sample on the vise by 90 degrees back and forth. This method is not compatible if the plating thickness exceeds 2 mm.

(4)Thermal-shock test

This test measures the adhesiveness by a heat shock when the heated sample is rapidly cooled down. Heat up the sample in the furnace until it reaches to the temperature shown in [Table 1]. Then, remove the sample and quench it in room-temperature water.

[Table 1] Furnace and test temperature

This section of JIS defines the conditions for significant surfaces of tin coatings electroplated on a metal substrate in order to improve solder wettability and anti-corrosion properties in electrical components.

(1) Grade and minimum plating thickness

The plating grades are classified into five categories as shown in [Table 1] based on the minimum plating thickness.

[Table 1] Grades and minimum plating thickness for electroplated coatings of tin

The base-coat plating will be determined and agreed between the parties concerned.

(2) Plating quality

Here are the assessment items for determining the quality of plating films.

1. Appearance

The plating type of either bright or matte plating will be determined and agreed between the parties concerned. However, note that the plating surface must be flat and free from burnt or swelling areas, lumps, pits, or exposure of substrates or base-coat plating.

2. Minimum plating thickness

This thickness must conform to [Table 1].

3. Corrosion resistance

This property can be measured by a salt spray test, etc.

4. Adhesiveness

This property can be measured by any of the following: tape test, bend test, or thermal-shock test.

5. Solder wettability

Perform a solder wettability test by immersing the test item into melted solder.

6. Stress relief before plating

If a stress relief of the steel substrate is required, determine the conditions between the parties concerned.

7. Heat treatment after plating

If a bright finish after plating or heat treatment is required for hydrogen embrittlement removal and whisker prevention, determine the conditions between the parties concerned.

(3) Plating name and symbol

Plating names are described by the symbols shown in this table.

In the next volume, we will learn about the plating bond test.