Custom Precision
Electrical Contacts

Ra 0.1μm on silver and gold contact faces is achieved by single-pass PCD (polycrystalline diamond) turning at optimized cutting parameters: v_c = 300–500 m/min for silver (10–20× higher than standard carbide cutting speed); feed rate f = 0.02–0.03mm/rev (below the nose radius-governed Ra threshold for the 0.2mm nose radius PCD insert used); depth of cut 0.020–0.050mm (single finish pass, no re-entry roughness artifact). At these parameters, the tool-workpiece contact is in the hydrodynamic cutting regime where the chip separates cleanly from the substrate without the built-up edge and stick-slip mechanisms that produce Ra 0.4–0.8μm from standard carbide tooling. The critical importance of Ra 0.1μm for contact resistance: contact resistance R = ρ/(2a) depends on the true contact area through the effective contact radius a. Two contacting surfaces with Ra 0.4μm asperities develop approximately 200 asperity contact spots per mm² at 1N contact force, with effective contact radius a_total ≈ 15μm. At Ra 0.1μm, 800 asperity contacts per mm² develop at the same 1N force, with a_total ≈ 30μm — the smoother surface produces 2× larger effective contact radius and 2× lower constriction resistance (R = ρ/(2a) halves when a doubles). For a silver contact: R at Ra 0.4μm ≈ 530 mΩ; R at Ra 0.1μm ≈ 265 mΩ — a 2× contact resistance reduction purely from surface finish improvement at constant contact force. For precision signal relay contacts where target contact resistance is ≤25 mΩ (achieved by gold plating providing oxide-free contact), the substrate surface finish under the gold plating must be Ra ≤0.2μm to ensure the gold plating deposits conformally rather than following asperity peaks — non-conformal gold plating on rough substrates has gold thickness variation that exposes substrate copper or nickel at asperity peaks faster than on a smooth substrate, reducing service life.

Beryllium copper (CDA 172, 1.9% Be) spring contacts achieve their high spring force through precipitation hardening — the metallurgical transformation from annealed (solution treated, A condition: yield strength ≈ 200 MPa) to aged (H900 condition: yield strength ≈ 1,100–1,380 MPa) that converts the initially soft, ductile alloy into a high-strength spring material. The processing sequence that CNCPioneer's BeCu spring contact programs follow is: machine in A (annealed) condition → age harden → verify post-age dimensions and spring force → plate. This sequence is mandatory because age hardening (3 hours at 315°C / 600°F) produces predictable dimensional changes — typically 0.003–0.008mm shrinkage on machined OD features from the precipitation-induced lattice contraction — that can be pre-compensated in the machining program. If machining were attempted after age hardening, the material's HV 350–400 hardness would require carbide at HSM parameters, and the achievable surface finish would degrade to Ra 0.8–1.6μm versus Ra 0.4μm from annealed BeCu — unacceptable for spring contact surface programs. The pre-age machining dimensions are adjusted for predicted age hardening distortion: for a spring arm 0.500mm thick with expected 0.005mm shrinkage in the thickness direction, CNCPioneer machines to 0.505mm in A condition — after aging, the arm thickness shrinks to 0.500mm ±0.003mm. Post-age dimensional verification confirms that every BeCu spring contact is within ±0.010mm of final drawing specification before plating investment. The age hardening is performed at qualified heat treatment facilities with furnace temperature uniformity ±5°C, documented furnace charts, and hardness verification (Rockwell C 38–44 for H900 CDA 172) on every BeCu contact lot — the metallurgical quality documentation that ensures the designed spring force is achieved in every assembled contact.