Press-fit terminal connection structure having types of alloy layer

A press-fit terminal connection system comprising:

• a printed circuit board having a through hole, the through hole including a tin layer on an outermost surface of an inner peripheral surface and at least a contact point portion on the tin layer;
• and
• a press-fit terminal having a board connecting portion configured to be press-fit into the through hole of the printed circuit board such that the through hole and the press-fit terminal are electrically in contact at a contact point portion of the press-fit terminal and the contact point portion on the tin layer of the through hole, the press-fit terminal including:
• an alloy containing layer having a domain structure of alloy parts and tin parts, the alloy parts being made of an alloy mainly containing tin and palladium, and the tin parts are made of pure tin or an alloy having a higher ratio of tin to palladium than the alloy parts, both the alloy parts and the tin parts being exposed on an outermost surface of the press-fit terminal;
• a base;
• and
• a nickel under layer disposed between the alloy containing layer and the base, the nickel under layer being composed of a nickel-tin alloy layer and a pure nickel layer, the nickel-tin alloy layer being disposed between the alloy containing layer and the nickel layer, and the nickel layer being disposed between the nickel-tin alloy layer and the base, wherein:
• a content of palladium in the alloy containing layer is 2 atomic % or higher;
• and
• a surface hardness of the alloy containing layer is 120 Hv or greater and 380 Hv or less.