Terminal structure, printed wiring board, module substrate, and electronic device

1. A terminal structure comprising:

a terminal having:

a conductor layer containing at least one metal selected from gold, silver, and copper;

a first layer containing nickel and phosphorus, laid on the conductor layer;

a second layer having a smaller atomic ratio of nickel to phosphorus than the first layer and containing Ni 3 P, laid on the first layer;

a third layer containing a first internetallic compound of an Ni—P—Sn type, laid on the second layer; and

a fourth layer containing a second intermetallic compound of an Ni—Cu—Sn type, laid on the third layer; and

a solder layer on the fourth layer of the terminal,

wherein Ra2 is larger than Ra1, where Ra1 is a surface roughness of the third layer on the second layer side and Ra2 is a surface roughness of the third layer on the fourth layer side.

2. The terminal structure according to claim 1 , wherein Ra1 and Ra2 satisfy Formula (1) below:

Ra 2 /Ra 1>1.5  (1).

3. A printed wiring board comprising the terminal structure as set forth in claim 1 .

4. An electronic device on which the printed wiring board as set forth in claim 3 is mounted.

5. A module substrate comprising the terminal structure as set forth in claim 1 , and an electronic instrument electrically connected to the conductor layer in the terminal structure.

6. An electronic device on which the module substrate as set forth in claim 5 is mounted.