Pre-Treatment: Brass must be thoroughly cleaned (degreased, pickled) to remove oxides and oils. A cyanide-based strike bath is often used for adhesion (e.g., before nickel plating). Multi-Layer Systems: Example: Ni (barrier) + Au (top layer) for high-performance contacts. Example: Cu (undercoat) + Ni + Cr for decorative finishes. Post-Plating: Passivation: Chromate coatings for zinc-plated
Author: Robby
Brass (a copper-zinc alloy) can be plated with various metal layers to enhance its conductivity, corrosion resistance, solderability, or aesthetic appeal. Below are the common metal platings applied to brass, along with their purposes and typical applications:
Purpose:
Provides excellent corrosion and wear resistance.
Acts as a barrier to prevent zinc leaching from brass.
Types:
Electroless Nickel (Ni-P or Ni-B): Uniform coating, no electricity needed.
Electroplated Nickel: Thicker, more durable layers.
Applications:
Marine hardware, plumbing fixtures, electrical connectors.
Purpose:
Hard, decorative finish with high corrosion resistance.
Often applied over nickel (Ni/Cr plating).
Applications:
Automotive trim, faucets, decorative hardware.
Purpose:
Improves electrical conductivity (ideal for RF/EMI shielding).
Prevents oxidation of brass contacts.
Applications:
High-frequency connectors, relay contacts, audiophile components.
Purpose:
Cost-effective solderability enhancement.
Precludes oxidation in humid environments.
Types:
Matte Tin: Standard for solderable surfaces.
Bright Tin: Aesthetic appeal (less common).
Applications:
Electrical terminals, PCB contacts, low-voltage busbars.
Purpose:
Superior oxidation resistance and low contact resistance.
Often plated over nickel (Ni/Au) for durability.
Types:
Hard Gold (Au-Co or Au-Ni alloys): Wear-resistant (e.g., connectors).
Soft Gold (Pure Au): For wire bonding (e.g., semiconductors).
Applications:
High-reliability electronics (aerospace, medical devices).
Purpose:
Tarnish-resistant alternative to gold (lower cost).
Used in sliding electrical contacts.
Applications:
Automotive switches, MEMS devices.
Purpose:
Extremely hard, reflective, and corrosion-resistant.
Used for high-end decorative items.
Applications:
Luxury jewelry, premium watch components.
Purpose:
Rarely plated onto brass (since brass is already copper-based), but used to repair or build up thickness.
Applications:
Electroforming, artistic metalwork.
Purpose:
Low-cost corrosion protection (e.g., galvanic coating).
Often chromate-passivated for color (yellow, blue, or clear).
Applications:
Fasteners, outdoor hardware.
Purpose:
Improved solderability (now restricted due to RoHS).
Replacements:
Tin-bismuth (Sn-Bi) or tin-silver (Sn-Ag) alloys.
| Plating | Key Benefit | Limitations | Typical Use Case |
|---|---|---|---|
| Nickel | Corrosion/wear resistance | Can cause nickel allergies | Marine hardware, electrical contacts |
| Silver | High conductivity | Tarnishes without coating | RF connectors, audiophile gear |
| Gold | Oxidation-free, reliable contacts | Expensive | Medical devices, aerospace |
| Tin | Solderability, low cost | Whiskering risk (mitigated with annealing) | PCB terminals |
| Chromium | Decorative, hard finish | Requires nickel underlayer | Automotive trim, faucets |
Pre-Treatment:
Brass must be thoroughly cleaned (degreased, pickled) to remove oxides and oils.
A cyanide-based strike bath is often used for adhesion (e.g., before nickel plating).
Multi-Layer Systems:
Example: Ni (barrier) + Au (top layer) for high-performance contacts.
Example: Cu (undercoat) + Ni + Cr for decorative finishes.
Post-Plating:
Passivation: Chromate coatings for zinc-plated brass.
Annealing: For tin-plated brass to prevent whiskering.
For electrical contacts: Silver or gold (Ni underlayer recommended).
For solderable parts: Matte tin or tin-bismuth.
For harsh environments: Nickel or nickel + chromium.
For decorative items: Chromium, rhodium, or gold.