Surface Roughness Effects on Contact Resistance in High Frequency Test Sockets
Surface roughness forces high-frequency current through isolated micro-asperities, increasing contact resistance and insertion loss as skin depth shrinks.
Profilometry
Meaning
Surface measurement technique used to extract topographical data and evaluate the roughness and step heights of a material surface. Employing profilometry allows engineers to verify that the micro-features of a substrate conform to the required manufacturing tolerances. This methodology is used to characterize both printed circuit boards and silicon wafers before subsequent processing steps.
It provides quantitative data on surface finish and layer thicknesses.
Contact Methodology
Stylus-based measurement relies on a fine diamond tip that scans physically across the surface under a very light load. The mechanical movement of the stylus during profilometry runs is converted into a high-resolution electrical signal that maps the height variations. This approach is highly accurate for measuring step heights but can potentially scratch soft materials if the contact force is too high.
Optical Alternatives
Non-contact methods use light interference to capture three-dimensional surface maps without physical contact. This optical profilometry prevents damage to delicate structures and allows for rapid scans of large surface areas. This speed makes it highly useful for high-volume inline production monitoring.
Process Validation
Printed circuit board fabrication relies on these measurements to control the quality of traces and the uniform deposition of solder mask. Engineers use the collected roughness profiles to adjust plating speeds and chemical mixtures in the bath, preventing issues like poor solder wetting or delamination of trace coatings. This routine analysis verifies that the physical properties of each production batch match the original electrical and thermal design requirements.