Silver is only 5% more conductive than copper. On that basis alone, you'd be hard-pressed to justify the 15–20% cost premium of silver-plated conductors in micro coaxial cable . Five percent improvement in bulk conductivity doesn't seem worth the added material and processing cost—and if the cable were carrying DC current, it wouldn't be.
But micro coaxial cables don't carry DC. They carry RF signals at megahertz frequencies where the skin effect concentrates current flow into a surface layer just a few micrometers thick. At that point, the conductor surface—not the bulk—determines the cable's electrical performance. And that's where silver plating transforms from a marginal upgrade into a meaningful engineering choice.
The Skin Effect: Why the Surface Matters More Than the Core
At DC, current distributes uniformly across a conductor's cross-section. As frequency increases, electromagnetic fields push current toward the outer surface—the skin effect. The characteristic depth at which current density drops to 37% of the surface value is called the skin depth (δ), and it's inversely proportional to the square root of frequency.
For copper at room temperature: skin depth at 1 MHz is about 66 μm, at 5 MHz it's about 29 μm, at 10 MHz it's roughly 21 μm, and at 20 MHz it drops to about 15 μm.
Now consider a 42 AWG micro coaxial cable with a 7×50 AWG stranded conductor. Each individual strand is approximately 25 μm in diameter. At 5 MHz, the skin depth (29 μm) is already comparable to the strand diameter—meaning current is flowing predominantly at the surface of each strand. At 10 MHz, the skin depth is smaller than the strand, and surface conductivity dominates the cable's resistive loss.
Silver's electrical conductivity is 6.30×10⁷ S/m versus copper's 5.96×10⁷ S/m—a 5.7% advantage. But that 5.7% is concentrated exactly where the current flows at operating frequencies above a few MHz. The effective improvement in cable attenuation at 10 MHz is typically 5–8%, and at 20 MHz it reaches 10–15%, because the thinner skin depth means a higher proportion of the conducting cross-section is silver rather than copper.
What Silver Plating Actually Looks Like at Micro Scale
The silver plating process for micro coaxial cable conductors is electroplating—the copper wire passes through a silver cyanide or silver nitrate bath under controlled current density. For 50 AWG strands (25 μm diameter), the plating thickness is typically 2–5 μm. That sounds thin, but on a 25 μm conductor, a 4 μm plating layer represents 16% of the strand radius—a substantial proportion of the cross-section where current actually flows at RF frequencies.
Plating Uniformity Is Everything
Here's what nobody tells you: the advertised plating thickness is a nominal value, and on micro-scale conductors, maintaining uniform thickness around the full circumference is genuinely difficult. The wire passes through the plating bath at speed, and current density varies around the conductor cross-section depending on bath geometry and wire tension. We've cross-sectioned incoming conductor lots and measured plating thickness variation of ±1 μm on a 3 μm nominal specification—meaning some spots have 2 μm coverage while others have 4 μm.
At 2 μm minimum thickness, the silver layer is still providing RF benefit (the skin depth at 10 MHz is 21 μm, so even 2 μm of silver on the surface improves surface conductivity). But if the plating drops below about 1.5 μm at any point, the silver becomes discontinuous—pinholes form, exposing bare copper that will oxidize over time. This is why we spec incoming silver-plated conductor with a 3 μm minimum rather than the 2 μm minimum that some suppliers offer. The extra micrometer provides margin against plating variation.
The Oxidation Advantage: The Benefit Nobody Talks About Enough
The high-frequency conductivity improvement gets all the attention, but silver plating's oxidation resistance is arguably more important for cable assembly reliability—especially in medical Applications .
Bare copper oxidizes. Exposed to air, copper develops a thin oxide layer (Cu₂O initially, then CuO) that increases surface resistance. At room temperature and normal humidity, this happens slowly—a fresh-stripped conductor will show measurable oxidation within days, but the practical impact on soldering and contact resistance takes weeks to become significant. Under autoclave sterilization (134°C, steam), oxidation accelerates dramatically. We've measured 3–5× increases in conductor surface resistance on bare copper after 50 autoclave cycles.
Silver tarnishes—it reacts with sulfur compounds in the air to form silver sulfide (Ag₂S). But silver sulfide is a much better conductor than copper oxide. A tarnished silver surface still solders cleanly and maintains low contact resistance. In the roughly 15,000 terminations we process monthly, first-pass solder wetting rates on silver-plated conductor are consistently 98–99%, versus 93–96% on bare copper (and that bare copper number drops to 85–90% if the wire has been stored unsealed for more than 60 days).
For reusable medical devices that get autoclaved hundreds of times, the silver plating's function as an oxidation barrier is often more valuable than its RF conductivity improvement. The conductor surface that was soldered during assembly stays stable through the device's entire service life—something bare copper simply can't guarantee.
When Bare Copper Makes Sense
Silver plating isn't always worth the cost. There are legitimate Applications where bare copper is the right engineering choice:
| Application Criterion | Silver-Plated Copper (SPC) | Bare Copper |
|---|---|---|
| Operating Frequency | Best above 2 MHz where skin effect dominates | Acceptable below 2 MHz |
| Sterilization Exposure | Required for autoclave, recommended for EtO/H₂O₂ | Acceptable for factory pre-sterilized single-use |
| Service Life | Reusable devices (years of use) | Single-use or short-life Applications |
| Storage Before Assembly | Tolerates months of storage without degradation | Must be processed within weeks of stripping |
| MRI Compatibility | Preferred—lower magnetic susceptibility than copper | Acceptable but higher artifact potential |
| Solderability | Consistent solder wetting throughout cable life | Wetting degrades with oxidation over time |
| Phase Stability Over Temperature | Better—silver's TCR is more stable than oxidized copper | Acceptable for single-temperature applications |
| Relative Cable Cost Impact | +15–20% vs. bare copper | Baseline cost |
Single-use endoscope cables operating below 5 MHz are the clearest case for bare copper. The cable gets used once, never sterilized, and thrown away. The 15–20% cost reduction from eliminating silver plating drops straight to the BOM—meaningful at volumes of 50,000+ units per year. We supply both options and leave the decision to the customer's engineering team based on their specific operating frequency and cost targets.
Silver Plating and MRI Compatibility
There's a secondary benefit of silver plating that's increasingly relevant: magnetic susceptibility. Silver has a volume magnetic susceptibility of −24×10⁻⁶ (diamagnetic), while copper is −9.6×10⁻⁶. Both are non-ferromagnetic and MRI-safe, but silver creates slightly smaller susceptibility artifacts in the MR image because its susceptibility is closer to that of water (−9.0×10⁻⁶).
In practice, this matters most for cables used inside or very near the MRI bore during scanning—such as MRI RF coil cables or interventional MRI device cables. For cables that are present in the MRI room but not inside the bore during acquisition, the susceptibility difference between silver and copper is academic. But for cable designers who need to minimize every source of image artifact, silver plating on the conductor (and on the shield, if budget allows) is one more lever to pull.
The Manufacturing Nuance: Plating Before or After Stranding?
Micro coaxial cable conductors are stranded—typically 7 individual strands twisted together. The silver plating can be applied at two points in the process: to the individual strands before stranding (the standard approach) or to the finished stranded conductor after stranding.
Plating individual strands is the norm because each strand gets uniform 360° plating coverage. Post-stranding plating risks leaving the contact surfaces between strands unplated—the plating solution can't penetrate the interstices of a tightly stranded conductor. Those unplated inter-strand surfaces become oxidation sites that increase AC resistance over time, partially negating the benefit of the silver plating on the outer surface.
We exclusively use pre-stranding plated conductor. It costs slightly more because the individual 50 AWG strands must be plated at very precise current density to avoid plating buildup that would change the strand diameter and throw off the finished conductor dimensions. But the result is a conductor where every surface—outer, inner, and inter-strand—is silver, giving you the full oxidation protection and RF performance benefit across the entire conductor cross-section.
The Practical Recommendation
For any micro coaxial cable operating above 5 MHz in a reusable or sterilizable device: specify silver-plated copper conductor. The 15–20% cost premium pays for itself through improved solderability, oxidation resistance, and lower attenuation. For single-use devices below 5 MHz where every penny of BOM matters: bare copper is defensible. For phase-matched multi-channel bundles , silver plating's stable surface conductivity provides slightly better phase consistency over temperature and aging—an incremental benefit that's worth capturing when you're already spending significant effort on phase matching.
Anyway—silver plating is one of those specifications that experienced cable engineers rarely debate. It's standard for medical micro coaxial cable for good reason. The more interesting question is plating thickness, and there the answer depends on your frequency range, sterilization method, and required service life. The data above should give you enough to make that call for your specific application.
Related Products
FRS Technology builds these assemblies to order - core count, gauge, jacket, connector and length to your drawing. Products relevant here:
Have an existing cable to match or replace? Send us the sample or spec for a like-for-like quote.
