Why Bump Metal Matters

An RFID inlay carries a tiny die bonded to an antenna. The joint between them must survive lamination heat, card flexing, humidity and years of field use, while staying cheap enough for a disposable label. The bump metal sets the bonding temperature, the contact resistance and the long-term corrosion behaviour of that joint.

Gold Stud Bumps

Gold has been the reference interconnect metal for decades. It does not oxidise, forms reliable thermocompression joints, and tolerates a wide process window - which is exactly why it is still specified for high-reliability cards.

• No oxide layer, so bonding is stable and repeatable.
• Excellent corrosion resistance in humid and salt environments.
• Highest material cost per die - significant at label volumes.

Copper Pillars and Copper Bumps

Copper offers similar electrical performance at a fraction of the metal cost, and supports finer pitch than gold studs. The trade-off is oxidation: copper needs a protective finish or an inert bonding atmosphere, and the process window is narrower.

• Much lower material cost - the main reason for adoption at volume.
• Supports finer pitch and higher I/O density than gold studs.
• Requires oxidation control: surface finish, flux or inert gas.

Silver and Silver-Filled Adhesive

Silver appears mainly as a filler in conductive adhesive rather than as a formed bump. It bonds at low temperature, which protects heat-sensitive antenna substrates, but silver can migrate under bias and humidity if the joint is not properly encapsulated.

• Lowest process temperature - safe for PET and paper substrates.
• No thermocompression tooling required.
• Watch for silver migration; encapsulation and testing are essential.

Chip attach station where interconnect bumps join the RFID die to the antenna.

Matching Metal to Application

Disposable UHF labels justify copper or silver adhesive because unit cost dominates and service life is short. Payment and national ID cards justify gold because a field failure is far more expensive than the metal. Most producers run more than one metallurgy and route jobs by product class.

Selection Quick Reference

Choose bump metallurgy from the product's service life, not from the datasheet price alone. Gold remains the safe default for long-life cards, copper is the volume workhorse when oxidation is controlled, and silver adhesive earns its place wherever the thermal budget rules out thermocompression.