Bare copper tarnishes in air and from handling. Buyers often ask whether passivation plus a seal will pass 96-hour neutral salt spray (NSS). That question only has an answer when the drawing already names the alloy, the finish family, which faces must stay conductive, the test method and what counts as a fail.
Use this checklist for OEM stamped copper parts such as busbars, terminals, contacts and hardware. It is for writing the RFQ, not for choosing a bath. It does not treat 96 hours as a factory-wide result.
Short answer: what the RFQ must include
Send the stamped-part drawing, copper grade and temper, the finish route, and which faces are cosmetic versus electrical. If salt spray is a real acceptance item, write the method, hours and fail rule on the same drawing. Do not copy hours from a coupon or a chemical data sheet.
The supplier should not have to guess whether the finish is for appearance, tarnish delay, electrical contact or a corrosion test.
- Alloy, temper, thickness and whether substitutions need written approval.
- Passivation, sealing, plating or a combination.
- Contact, crimp, solder and cosmetic zones on the drawing.
- Salt-spray standard, hours, fail definition and whether the test is in the quote.
- Packing, fingerprint control and any required RoHS or REACH records.
Name passivation, sealing or plating
These three are not the same treatment. Passivation is a thin film on the copper, usually for appearance and short-term tarnish delay. Sealing is an extra layer after that; it can raise contact resistance if it covers pads. Plating replaces the copper surface with another metal, such as tin, nickel or silver.
If the RFQ only says anti-tarnish or passivate, suppliers will assume different processes and whether a seal is included. Name the route, or ask engineering to propose one. If hexavalent chromium is forbidden, say so. Do not put a product name on a production drawing until that chemistry is approved.
- Passivation: thin film for appearance and short-term tarnish delay.
- Sealing: extra barrier after passivation; keep it off named contact pads unless allowed.
- Plating: another metal surface; specify the standard, thickness, underplate and masking.
Mark contact, crimp and solder faces
A seal can raise contact resistance and can interfere with solder or crimps. On busbars, terminals and grounds, mark pads that must stay bare, be selectively plated, or be checked to a milliohm limit. A part can pass salt spray and still fail the joint.
Selective finishing needs a map: finish on cosmetic faces, tin or nickel on pads, or mask then plate. Plating buildup changes hole fit. State whether dimensions apply before or after finishing.
Write the salt-spray note so quotes can be compared
Salt-spray testing can be arranged to the method, hours and acceptance agreed for the project. Records are provided when they are in the quotation and quality plan. ISO 9227 and ASTM B117 describe how to run the test; they do not set 96 hours or the fail rule. A line that only says 96 hours is not a specification.
A usable note names the standard, NSS rather than a more aggressive atmosphere, hours, sample quantity, how the part is mounted, and what counts as a fail: colour change, wipe-off products, red rust on steel hardware, or a resistance shift. Without those, two suppliers can both say 96 hours and mean different tests.
Cleaning, handling and packing still belong on the RFQ
Stamped copper carries press oil and fingerprints. The finish will not hold if the part is dirty, stacked wet, or handled bare after treatment. If parts will sit between stamping and finishing, say so. Ask for trays or bags that protect treated faces in transit.
- Parts must be clean of stamping oil before finishing.
- Dry fully before stacking, bagging or salt-spray loading.
- Protect treated faces from scratches and fingerprints.
- State storage time if stamping and finishing are not back-to-back.
| Buyer requirement | Why it matters | What to write |
|---|---|---|
| 96-hour salt spray | Hours without a method and fail point cannot be compared | Standard, NSS, hours, quantity, fail definition |
| Passivation only | Thin film; oil and handling can erase it | Process family, appearance target, no-touch packing |
| Passivation plus seal | Better barrier; may cover electrical pads | Seal allowed or forbidden on named contacts |
| Plating | Different surface; buildup and masking change fit | Spec, thickness, underplate, selective map |
| Contact resistance | A passing coupon can still make a poor joint | Pad locations and any milliohm or continuity check |