Copper Strip Testing

Copper strip inspection mainly conducts scientific testing and analysis on the chemical composition analysis, mechanical property testing, electrical property testing, dimension and shape precision testing, surface quality inspection and metallographic structure analysis, objectively assessing the product quality grade and issuing a detailed test report, providing a basis for manufacturers' quality control and downstream users' product acceptance.

Testing Items

Chemical composition analysis: Through the means such as the spectroscopic methods, the contents of the copper (Cu) and other alloying elements (such as the zinc, tin, nickel and phosphorus) in the copper strips are precisely determined. This is the basic testing of ensuring that the material designations meet the standards and satisfy the specific electrical conductivity, thermal conductivity or mechanical property requirements.

Mechanical property testing: Mainly evaluating the strengths, ductility and hardnesses of the copper strips. The key items include the tensile strength, yield strength, elongation after fracture and hardness (commonly the Vickers or Brinell hardness), directly related to the forming abilities and service lives of the copper strips in the subsequent processing such as the stamping and bending.

Electrical property testing: The electrical conductivity is one of the core performance indicators of the copper strips, usually expressed as the percentage of the International Annealed Copper Standard (IACS). The volume resistivities or electrical conductivities need to be tested, ensuring that they meet the strict requirements for the low resistance losses in the power transmission and electronic components.

Dimension and shape precision testing: Including the thickness, width and length tolerances, as well as the measurement of the edge states (burrs and cracks) and plate shapes (straightness and warpage). The high-precision dimension control is the key of guaranteeing the automatic assembly and product consistency.

Surface quality inspection: Under the good lighting conditions, whether the copper strip surfaces have the defects such as the oxidation, discoloration, scratches, indentations, peeling, inclusions and oil stains is visually checked or with the help of the magnifying devices. The surface qualities directly affect the subsequent plating, welding and appearances.

Metallographic structure analysis: Through the specimen preparation and etching observation, the grain sizes, twin quantities, inclusion distributions of the copper strips are analysed, and whether the abnormal structures such as the overheating and overburning exist. The metallographic structures are closely related to the mechanical properties and process properties of the material.

Testing Scope

Pure copper strips: Such as the T2 red copper strips. The testing emphases are the extremely high electrical and thermal conductivity, good plasticity and the corresponding chemical composition purity. Mainly applied to the electrical fields such as the transformers, radiators and busbars.

Brass strips: The copper-zinc alloys. The testing needs to pay attention to the zinc contents and their effects on the strengths, cutting properties and corrosion resistance. Widely used for the hardware parts, locks, musical instruments and decorative strips.

Bronze strips: Mainly referring to the tin bronzes and phosphorus bronzes. The testing focuses on the contents of the elements such as the tin and phosphorus, as well as the resulting high strengths, high elasticity, wear resistance and fatigue resistance. Often used for the spring leaves, connectors and bearing bushes.

Nickel silver strips: The copper-nickel alloys. The testing core is the nickel contents and the resulting excellent corrosion resistance, anti-marine-biofouling properties and medium strengths. It is the key material of the heat exchangers, marine equipment and precision resistors.

Lead frame copper strips: A type of high-performance copper alloy strips. The testing requirements are extremely strict, covering the ultra-high strengths, high electrical conductivity, heat-softening resistance, low residual stresses and perfect surface and dimension precision, used for the integrated circuit packaging.

Products of the different states: The testing needs to distinguish the products of the different work hardening states such as the soft state (M), half-hard state (Y2) and hard state (Y), whose mechanical property indicators and testing standards have the significant differences.

Testing Methods

Spectroscopic analysis method: The spark direct-reading spectrometers (OES) or inductively coupled plasma optical emission spectrometers (ICP-OES) are used for the fast and multi-element simultaneous determination of the chemical compositions. The former is suitable for the on-site fast analysis, and the latter has the higher precision and can analyse the trace elements.

Tensile testing method: According to the standards such as GB/T 228.1 or ASTM E8, the axial tensile forces are applied to the standard specimens on the universal material testing machines until the fracture, thereby obtaining the stress-strain curves and calculating the tensile strengths, yield strengths and elongations after fracture.

Electrical conductivity testing method: The eddy current conductivity instruments (according to GB/T 3048.2 or ASTM B193) are commonly used. Using the eddy current principle, the electrical conductivity values of the copper strips are non-destructively measured. For the high-precision requirements, the DC resistance-mass method (four-terminal method) can be adopted.

Metallographic inspection method: According to GB/T 6394 or ASTM E112, after the mounting, grinding, polishing and etching of the sampled specimens, the observation and photographing are carried out under the metallographic microscopes, and the grain size grades are rated using the comparison method or intercept method.

Dimension measurement method: The thicknesses and widths use the high-precision micrometers, callipers or online thickness gauges; the lengths use the tapes or length counters; the straightness can be quantitatively evaluated using the platform and feeler gauge method or laser straightness instruments.

Hardness testing method: According to the copper strip thicknesses and states, the Vickers hardness (HV), Brinell hardness (HB) or Rockwell hardness (HRB) testing is selected. The Vickers hardness is suitable for the thin strips and tiny areas, and the Brinell hardness has the large indentations and good representativeness.

Testing Standards

Domestic Standards:

1. GB/T 2059, Copper and copper alloy strip

2. GB/T 228.1-2021, Metallic materials — Tensile testing — Part 1: Method of test at room temperature

3. GB/T 3048.2, Test methods for electrical properties of electric wires and cables — Part 2: Test of metallic material resistivity

4. GB/T 6394-2017, Determination of estimating the average grain size of metal

International Standards:

1. ISO 6892-1, Metallic materials — Tensile testing — Part 1: Method of test at room temperature

2. ASTM E8, Standard test methods for tension testing of metallic materials

3. ASTM B193, Standard test method for resistivity of electrical conductor materials

4. ASTM E112, Standard test methods for determining average grain size

Note: The applicable standard can be selected according to the product use and customer trade requirements; standards agreed in the contract take precedence over general standards.

Testing Instruments and Equipment

Direct-reading spectrometer: Used for the fast quantitative analysis of the chemical compositions. The equipment generates the characteristic spectra through the excitation of the samples, receives them by the detectors after the grating dispersion, and directly outputs the percentage contents of the various elements by comparing with the standard sample database.

Universal material testing machine: The core equipment of carrying out the mechanical testing such as the tensile, bending and compression. Equipped with the high-precision load transducers and extensometers, the computer control systems control the loading speeds and collect the data in real time, automatically generating the test reports.

Eddy current conductivity instrument: Used for the fast and non-destructive electrical conductivity testing of the copper strips. The instrument probes generate the high-frequency alternating magnetic fields to induce the eddy currents in the copper strips. The reverse magnetic fields generated by the eddy currents affect the probe impedances, and the changes are related to the material electrical conductivities. After the calibration, the readings can be directly obtained.

Metallographic microscope and sample preparation equipment: Including the cutting machines, mounting machines, grinding and polishing machines and metallographic microscopes. The microscopes are equipped with the observation modes such as the bright field, dark field and polarized light, as well as the image analysis systems, used to observe, record and analyse the micro-structure organizations of the material.

Precision dimension measurement tools: Covering the digital micrometers (precision 0.001mm), large vernier callipers, radius gauges, platforms, feeler gauges, as well as the non-contact laser thickness gauges and profilometers. The online testing systems can realize the high-speed continuous monitoring of the widths and thicknesses.

Hardness tester: The Vickers hardness testers use the square pyramid diamond indenters, measuring the indentation diagonal lengths to calculate the hardnesses; the Brinell hardness testers use the cemented carbide ball indenters, measuring the indentation diameters. The equipment all needs to be regularly calibrated with the standard hardness blocks.