The reliability of printed circuit boards (PCBs) using RT-duroid 5870 material is influenced by the adhesion of copper foil to the substrate. This study examines the impact of soldering temperatures on copper foil adhesion. By exploring different thermal profiles and their effects, the study aims to provide insights into optimizing soldering processes for high-frequency and high-performance applications.

1. Introduction

RT-duroid 5870 is a high-frequency laminate known for its low dielectric constant, low dissipation factor, and excellent performance in microwave and radio-frequency (RF) applications. However, its thermal behavior during soldering processes is critical, as excessive temperatures can degrade copper adhesion. Understanding this relationship is vital to improving manufacturing yields and product reliability.

2. Material Overview

RT-duroid 5870 Material:

• Substrate: Glass microfiber reinforced PTFE.
• Dielectric constant: ~2.33 (at 10 GHz).
• Dissipation factor: ~0.0012 (at 10 GHz).

Copper Foil:

• Type: Rolled or electro-deposited.
• Thickness: Varies (common values: 17 μm to 70 μm).

3. Experimental Procedure

3.1 Sample Preparation:

• Copper-clad RT-duroid 5870 samples were prepared with varying copper foil thicknesses.
• The surfaces were cleaned to ensure consistent adhesion conditions.

3.2 Thermal Profiles:

• Temperature range: 200°C to 350°C.
• Time duration: 30 seconds to 120 seconds per profile.

3.3 Testing Adhesion Strength:

• Peel strength tests (ASTM D2861 standard) were conducted to measure adhesion.

4. Results and Discussion

4.1 Temperature Effects

• Adhesion strength increased moderately at temperatures below 250°C due to better resin reflow and copper bonding.
• A significant reduction in adhesion was observed beyond 300°C, attributed to PTFE degradation and copper oxidation.

4.2 Time Effects

• Extended soldering times amplified the thermal impact, accelerating adhesion degradation at higher temperatures.

4.3 Microscopic Observations

• SEM analysis revealed micro-cracking in PTFE and delamination patterns as temperatures exceeded 300°C.

5. Recommendations

1. Optimal Soldering Temperature: Maintain soldering temperatures between 220°C and 260°C to balance adhesion strength and thermal integrity.
2. Soldering Duration: Minimize exposure time at elevated temperatures.
3. Surface Treatments: Enhance copper adhesion using surface roughening or bonding agents before thermal processes.

The adhesion of copper foil to RT-duroid 5870 material is highly sensitive to soldering temperatures and duration. Maintaining controlled thermal profiles is essential for ensuring reliability in high-frequency applications. Further research into material enhancements and alternative processing techniques is recommended.