Peeling strength test of copper foil on flexible copper-clad laminate

Abstract: This article introduces the use of the Kunpeng BOYI 2025 electronic universal material testing machine, combined with a 500N pneumatic double-push tensile fixture and a flexible copper-clad laminate peeling fixture. According to Section 2.4.9-1 of the IPC-TM-650 Test Methods Manual, the peeling strength of the copper covering on flexible dielectric materials was tested. An example of peeling tests on flexible copper-clad laminates is provided. The peeling strength characterizes the adhesion strength between the copper layer and the substrate. Test results show that the Kunpeng BOYI 2025 electronic universal material testing machine can fully meet the requirements for peeling tests of flexible copper-clad laminates.

Keywords: Kunpeng BOYI 2025 electronic universal material testing machine, flexible copper-clad laminate, flexible dielectric material, peeling test

Flexible copper-clad laminate (FPC) is a highly reliable, excellent flexible printed circuit board made from polyimide or polyester film as the substrate. FPC is also known as flexible circuit board or flex circuit. By embedding circuit designs on a bendable thin plastic sheet, FPC allows stacking a large number of precision components in narrow and limited spaces, forming a flexible circuit that can bend and fold freely. It is lightweight, compact, has good heat dissipation, and is easy to install, breaking through traditional interconnection technologies. The structure of flexible circuits consists of insulating films, conductors, and adhesives. One important role of the adhesive is to bond the insulating film to the conductive material. The quality of this bonding affects the reliability and service life of the flexible copper-clad laminate. Therefore, testing the bonding strength is essential, which is characterized by peeling strength. This application introduces the peeling strength test of flexible copper-clad laminates.

The Kunpeng testing machine is equipped with a pneumatic double-push tensile fixture and a flexible copper-clad laminate peeling fixture, fully meeting the standard requirements. The pneumatic double-push fixture can quickly clamp samples, improving testing efficiency. The flexible copper-clad laminate peeling fixture is specially developed for this type of test, featuring high precision, low resistance, and accurate angle limiting, ensuring smooth peeling and angle maintenance during the test to guarantee accurate results. Besides the fixtures, the high precision of the testing machine's main unit and a data acquisition frequency exceeding 1000Hz can fully record all characteristic data during the peeling process, providing users with accurate and reliable test data. Coupled with intelligent testing software, it can simultaneously provide various test curves such as single sample, multiple samples, and dual coordinates, offering a good interactive experience for different users and supporting enterprises in research and development, quality, and product control.

1. Test Section

1.1 Instruments and Fixtures

BOYI 2025-001 Electronic Universal Testing Machine

500N Pneumatic Double-Push Tensile Fixture

Flexible Copper-Clad Laminate Peeling Fixture

Smartest Software

1.2 Analysis Conditions

Test Temperature: Approximately 20°C at room temperature

Load Sensor: 1000N (Class 0.5)

Loading Test Rate: 50.8 mm/min

1.3 Samples and Treatment

In this test, samples with a fixed bonding width of 3.00 mm were selected, and the copper foil surface was reinforced with special tape. The samples were pre-peeled to a certain distance, ensuring that the peeling end had good adhesion between the copper foil and the tape to avoid delamination or edge damage, preventing breakage during peeling. The peeling end length was sufficient to be fully clamped by the upper fixture. The peeling test requires that the fixture clamping end of the testing machine always maintains perpendicularity to the substrate during peeling.

2. Test Introduction

Using the BOYI 2025-001 electronic universal testing machine, the back of the sample's film layer was attached to the peeling fixture's rotating drum with double-sided tape, and the copper foil was clamped in the upper fixture, forming a perpendicular peeling state as shown below (Figure 1). The test was conducted at a rate of 50.8 mm/min. Force and displacement data during the peeling process were measured. The average peeling force during the peeling state was taken to obtain the peeling force and calculate the peeling strength data (Table 1), and peeling curves were generated (Figures 2-3).

Figure 1 Test System Diagram (Main Unit, Fixtures)

3. Results and Conclusions

3.1 Test Results

After the test, the load-displacement curves of the sample peeling test are shown in (Figures 2-3). During peeling, subtle force fluctuations were captured by the main unit, forming stable peeling curves. Using the testing software, load and displacement data can be obtained from the curves, as well as the average peeling strength. Specific test results are as follows (Table 1).

Figure 2 Peeling Curve (Multiple Samples)

Single Sample

Partial Enlargement

Figure 3 Peeling Curve (Single Sample)

                                                                                                          Figure 4 Sample Peeling State

Table 1. Test Results

      From the data above (Table 1) and the state of the peeled samples, it can be seen that throughout the entire test process, the peeling state of the samples was stable with very little fluctuation and no abnormal peeling phenomena. The average results of the 5 samples are very close, with the difference between the maximum and minimum values within 0.2 N/mm. The results of this test demonstrate the high precision and high stability of the Kunpeng BOYI 2025-001 electronic universal testing machine.

4. Conclusion

In summary, the Kunpeng BOYI 2025-001 electronic universal testing machine, 500N pneumatic double push-pull tensile fixture, and flexible copper-clad laminate peeling fixture can fully meet the requirements of Section 2.4.9.1 - Peel Strength of Cover Copper on Flexible Dielectric Materials in the IPC-TM-650 Test Methods Manual, efficiently and effectively completing the test. Through a high-precision, high-sampling-rate testing system, various mechanical data of the copper-clad laminate can be obtained reliably and stably. This is very important for the technological development of the flexible copper-clad laminate industry, providing data support and technical assurance for enterprises' product research and development, quality management, as well as the standardization and normalization of the industry.