Contact Pad

Contact Pad

The contact padcontact padHardwareGold electrical contacts on card surface.Click to view → (also called the chip module or contact plate) is the gold-plated metallic area on the surface of a contact smart card that provides the electrical interface between the card's embedded chip and the card reader. Defined by ISO 7816 Part 2, the contact pad consists of eight designated contacts (C1 through C8) arranged in a standardized layout, though not all contacts are used in every application.

Contact Pin Assignment

The I/O line (C7) carries all APDU communication using either T=0 or T=1 protocol. The clock on C3 drives the card's internal oscillator and determines the maximum baud rate for data transfer.

Physical Specifications

The contact pad module must meet strict dimensional requirements per ISO 7816ISO 7816StandardPrimary standard for contact smart cards.Click to view →-2:

• Minimum contact area: 1.7 mm x 2.0 mm per contact
• Position tolerance: within the defined contact zone on the card face
• Surface finish: Gold plating (minimum 0.5 microns) for corrosion resistance and reliable contact
• Contact resistance: less than 1 ohm per contact point

The module is embedded in the card body through a process called chip embedding, where a cavity is milled in the plastic substrate and the module is bonded with adhesive.

Dual-Interface Modules

Modern payment and identity cards increasingly use dual-interface modules that combine ISO 7816 contact pads with an antenna connection for ISO 14443ISO 14443StandardStandard for contactless smart cards.Click to view → contactless operation on a single chip die. The module has additional bonding pads (L1, L2) on its underside that connect to the card bodycard bodyHardwarePlastic substrate forming the card physical structure.Click to view → antenna through wire bonding or laser welding. This allows one chip to serve both contact (PIN entry at terminals) and contactless (tap-to-pay) transactions.

Wear and Reliability

Contact pads endure mechanical stress from repeated card insertions. ISO 7816-1 specifies a minimum of 10,000 insertion/withdrawal cycles. Common failure modes include gold plating erosion exposing the nickel or copper sublayer, oxidation of exposed metal, and flex fatigue cracking the wire bonds between the module and the chip die.