1. Introduction
In high-frequency PCB manufacturing, RT-duroid® 5870 laminates are widely recognized for their ultra-low dielectric constant (Dk ≈ 2.33), exceptionally low dissipation factor (Df ≈ 0.0012), and outstanding signal stability across microwave and RF frequency ranges. These properties make them ideal for critical applications such as radar systems, satellite communication, and 5G base station circuits.
However, achieving stable copper foil adhesion during soldering remains a key reliability challenge. Excessive thermal stress can cause PTFE matrix degradation, interfacial delamination, or oxidation of the copper surface, ultimately compromising circuit performance.
This study investigates how soldering temperature and duration influence copper adhesion strength on RT-duroid 5870 substrates, aiming to optimize thermal profiles for enhanced PCB reliability.
2. Material Overview
RT-duroid® 5870 Laminate
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Base Material: Glass microfiber reinforced PTFE
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Dielectric Constant (Dk): ~2.33 (at 10 GHz)
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Dissipation Factor (Df): ~0.0012 (at 10 GHz)
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Key Characteristics: Low moisture absorption, excellent dimensional stability, and uniform dielectric properties.
Copper Foil
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Type: Rolled or Electro-Deposited (ED)
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Thickness Range: 17 μm – 70 μm
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Surface Treatment: Standard micro-roughened bonding interface for improved adhesion.
3. Experimental Procedure
3.1 Sample Preparation
Copper-clad RT-duroid 5870 samples were fabricated under controlled lamination conditions. Surfaces were thoroughly cleaned and degreased to ensure uniform bonding. Multiple sets of samples were prepared with varying copper thicknesses to observe performance under different thermal stress levels.
3.2 Thermal Soldering Profiles
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Temperature Range: 200°C – 350°C
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Exposure Duration: 30 s, 60 s, 90 s, and 120 s
Each temperature profile simulated realistic reflow and wave soldering conditions commonly encountered in PCB assembly processes.
3.3 Adhesion Testing
Copper peel strength was evaluated according to ASTM D2861 using a standardized 90° peel test. Post-test samples were inspected with scanning electron microscopy (SEM) to identify microstructural changes at the copper/PTFE interface.
4. Results and Discussion
4.1 Temperature Effects on Adhesion
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Below 250°C: A moderate increase in adhesion strength was observed, likely due to localized reflow of PTFE that improved copper bonding.
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Between 260°C–300°C: Adhesion began to decline gradually as thermal softening and PTFE expansion introduced stress at the copper interface.
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Above 300°C: A sharp decrease in peel strength occurred, primarily due to PTFE decomposition and oxidation of copper foil, leading to visible interfacial delamination.
4.2 Influence of Soldering Duration
Longer soldering durations at elevated temperatures accelerated thermal degradation, causing a progressive reduction in adhesion strength. The combination of high heat and extended exposure resulted in microcracking of the PTFE matrix, further weakening the bond.
4.3 Microscopic Analysis
SEM observations revealed:
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Microcracks propagating through the PTFE reinforcement fibers.
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Interfacial voids and delamination zones above 300°C.
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Minor resin reflow and improved wetting below 250°C, correlating with increased peel strength.
5. Recommendations for PCB Fabrication
| Parameter | Recommended Range | Purpose |
|---|---|---|
| Soldering Temperature | 220°C – 260°C | Ensures strong adhesion without PTFE degradation |
| Exposure Time | ≤ 60 seconds | Prevents excessive thermal stress and delamination |
| Surface Preparation | Micro-etching or bonding agents | Enhances mechanical interlock and chemical bonding |
| Lamination Control | Uniform pressure and heat | Minimizes resin voids and air entrapment |
To further enhance adhesion reliability, manufacturers should adopt controlled thermal ramp profiles, implement copper surface roughening techniques, and consider adhesion-promoting coatings compatible with PTFE-based laminates.
6. Conclusion
The adhesion between copper foil and RT-duroid® 5870 is highly sensitive to soldering temperature and thermal exposure time. Maintaining process parameters within optimal limits (220°C–260°C, ≤60 s) ensures stable interfacial bonding and long-term PCB reliability.
In high-frequency PCB manufacturing, careful thermal management during soldering is crucial for preventing delamination, maintaining impedance stability, and achieving consistent electrical performance.
Future work will focus on developing enhanced copper surface treatments and modified PTFE composites to further improve bonding strength under high-temperature soldering conditions.
