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.
Copper Migration
Meaning
Electrochemical transport of copper ions across a dielectric substrate under the influence of an electric field creates conductive filaments that cause electrical shorts. Known as copper migration, this phenomenon typically occurs in the presence of moisture and ionic contamination on printed circuit boards. This process poses a major hazard to fine-pitch electronic assemblies operating in humid conditions.
It begins when copper dissolves at the anode and deposits at the cathode.
Growth Phase
Filament formation requires moisture and electrical bias to sustain the transport of dissolved ions. Once copper migration initiates, the resulting microscopic dendritic structures grow along the glass fibers of the board substrate. This progressive growth eventually bridges the gap, resulting in sudden breakdown.
Environmental Control
Protective measures must address both the moisture ingress and the chemical purity of the board during the assembly process. Applying conformal coatings restricts humidity from contacting the copper traces, while rigorous cleaning stages remove residual plating chemicals and solder flux. These steps prevent the formation of the conductive liquid film needed for ion transport.
Testing Protocol
Validation testing uses temperature and humidity chambers to accelerate the onset of these failures under high electrical bias. Technicians subject the boards to high-temperature humidity trials while monitoring insulation resistance in real time to detect the moment a filament forms. This measurement provides the empirical data required to certify that the laminate materials and solder mask can resist the degrading effects of copper migration over the intended operating life of the product.