Selecting Dielectric Substrates for High Speed Multilayer Stackup Design
Selecting dielectric substrates requires balancing dissipation factor, glass weave uniformity, foil roughness, and panel yields to meet high-speed impedance targets.
ENIG Insertion Loss
Signal Attenuation
High frequency energy decreases as it propagates along copper traces finished with nickel and gold layers. The enig insertion loss quantifies the drop in power caused by the resistive properties of the electroless nickel layer. Because signal current flows mostly on the outer surface of a conductor at high speeds, it must pass through the nickel before reaching the gold.
Resistive Impact
Nickel has a much lower conductivity than the copper it protects, which creates a bottleneck for the electrical signal. An enig insertion loss becomes more pronounced as frequencies rise into the gigahertz range where the skin effect is strongest. High speed digital circuit designs often require alternative finishes when the power loss exceeds the link budget for the system.
The thickness of the nickel and the phosphorus content within that layer both contribute to the overall resistance of the circuit.
Frequency Variance
Testing involves comparing the power output of a trace against its input across a wide range of operating conditions. The enig insertion loss is typically measured using a vector network analyzer on specialized test coupons. Results show that while the finish provides excellent solderability and shelf life, its electrical performance requires careful modeling for transmission lines operating above five gigahertz.