Quantifying Hydrophobic Organosilane Surface Treatment Efficacy in Low Loss Microwave Substrates
Hydrophobic organosilane surface treatments on low-loss microwave substrates suppress moisture-induced Df drift and enable ultra-smooth copper foils.
Contact Angle Hysteresis
Wetting Resistance
Thermodynamic differences between advancing and receding liquid angles on a solid surface define the dynamic wetting properties of a substrate. Observation of contact angle hysteresis indicates the degree of molecular heterogeneity or physical roughness present on a circuit board substrate after chemical cleaning. Wetting is affected.
High values often suggest that a surface possesses extensive topographic variation that traps air or prevents uniform fluid spread.
Surface Cleanliness
Chemical residues left after etching or stripping modify how a liquid interacts with the copper or epoxy resin. When contact angle hysteresis increases, it signals that the surface is not chemically uniform. This lack of uniformity interferes with the consistent application of solder masks or conformal coatings.
Adhesion Influence
Mechanical bonding relies on the ability of a liquid resin to penetrate the microscopic valleys of a roughened surface. If the contact angle hysteresis is too high, the advancing liquid front may bridge over these valleys rather than filling them. This behavior results in micro-voids at the interface which weaken the long-term reliability of the assembly.
This failure mode becomes particularly evident during thermal cycling when the air trapped in these voids expands and generates localized stress. Reliability depends on it. Reliability engineers use these measurements to determine if a surface treatment is sufficient for high performance environments.