Precise testing of copper-clad boards hinges on systematically verifying their fundamental performance. Following these three steps ensures reliable results.
1. Before the test: Build a solid foundation
This is a crucial step that is often overlooked.
Sample Conditioning: The copper-clad laminate to be tested should be placed in a standard environment (e.g., 23°C, 50% relative humidity) for more than 24 hours to stabilize its performance. This is a prerequisite for ensuring the comparability of all test results.
Instrument Calibration: Ensure that measuring instruments such as micrometers and tensile machines are calibrated. Inaccurate tools render all measurements invalid.
II. Core Testing Items: Focus on the Key Points
There is no need to cover every aspect, but the following four items must be strictly controlled.
1. Appearance and Physical Dimensions
What to test: Surface defects (scratches, pits), thickness uniformity.
How to measure:
Visual inspection: Carefully observe under good lighting conditions.
Thickness: Measure at multiple points on the board using a digital micrometer and take the average value.
2. Peeling strength (key mechanical property)
What to test: The adhesion between copper foil and substrate.
How to measure:
Etch the sample to form copper strips of specific widths.
Use a tensile testing machine to uniformly lift the copper strip at a 90-degree angle, and record the force value.
Key Point: Determine whether the damage interface is in the adhesive layer or within the material itself, as this helps identify the root cause of the issue.
3. Immersion soldering resistance (critical thermal reliability)
What to test: The ability to resist high-temperature assembly.
How to measure:
Float the sample on molten solder at 288°C and immerse it for 10 seconds.
Key points: The sample must be thoroughly dried before testing; otherwise, internal moisture will evaporate when heated, causing the board to "burst" (delaminate and blister).
4. Dielectric Properties (Core of High-Frequency Circuits)
What to measure: dielectric constant and loss factor, which determine signal transmission speed and integrity.
How to measure:
A vector network analyzer and dedicated test fixtures are required.
Key Precision: Conduct tests at the actual usage frequency points of the product, and ensure the test fixtures are strictly calibrated; otherwise, the data will be meaningless.
III. The Golden Rules of Precision Testing
Comply with standards: Strictly adhere to industry standards such as IPC (e.g., IPC-TM-650) and national standards, which serve as the pass for achieving results.
Environment is one: Leaving the stable environment of constant temperature and humidity, any precision testing loses its significance.
Complete documentation: Record sample information, test conditions, operators, and all raw data in detail to ensure traceability of results.
Summary:
To accurately test copper-clad boards, follow this process: "First stabilize the samples, then calibrate the instruments; establish baseline measurements for appearance and dimensions, evaluate adhesion through peel strength, test thermal stability with immersion soldering resistance, and ensure dielectric performance for high-frequency applications; adhere to standards throughout the process and maintain complete data records." By mastering these key steps, you can effectively control the quality checkpoint of PCB substrates.
