Electronic component and method of manufacturing the same

1. An electronic component comprising an external terminal including a lead base material constituted of a predetermined metal material, and a metal thin film coating a surface of said lead base material and including at least a first layer constituted of a material substantially Pb-free and predominantly composed of tin,

wherein an average value of a crystal size index is not less than 7 when said crystal size index is defined as (a+b)/2, where a and b respectively represent dimensions in μm of a crystal particle constituting said first layer in a direction perpendicular to said lead base material surface and in a direction parallel thereto, taken on a cut surface of said first layer defined by a given plane cutting said first layer in a direction perpendicular to said lead base material surface.

2. The electronic component as recited in claim 1 , wherein said first layer is constituted substantially of pure tin, or a tin-based alloy predominantly composed of tin and containing as an additive metal at least one out of the group consisting of bismuth, silver, copper, indium and zinc.

3. An electronic component comprising an external terminal including a lead base material constituted of a predetermined metal material, and a metal thin film coating a surface of said lead base material and including at least a first layer constituted of a material substantially Pb-free and predominantly composed of tin,

wherein an average value of Xh/Xv is not less than 4, where Xv and Xh respectively represent dimensions of a crystal particle constituting said first layer in a direction perpendicular to said lead base material surface and in a direction parallel thereto, taken on a cut surface of said first layer defined by a given plane cutting said first layer in a direction perpendicular to said lead base material surface.

4. The electronic component as recited in claim 3 , wherein said first layer is constituted substantially of pure tin, or a tin-based alloy predominantly composed of tin and containing as an additive metal at least one out of the group consisting of bismuth, silver, copper, indium and zinc.

5. An electronic component comprising an external terminal including a lead base material constituted of a predetermined metal material, and a metal thin film coating a surface of said lead base material and including at least a first layer constituted of a material substantially Pb-free and predominantly composed of tin, wherein said first layer is formed by plating, and a total extended length of a crystal particle boundary of said first layer is not more than 300 μm per 1000 μm 2 of observation area, on a cut surface parallel to a surface of said lead base material.

6. The electronic component as recited in claim 5 , wherein said first layer is constituted substantially of pure tin, or a tin-based alloy predominantly composed of tin and containing as an additive metal at least one out of the group consisting of bismuth, silver, copper, indium and zinc.

7. An electronic component comprising an external terminal including a lead base material constituted of a predetermined metal material, and a metal thin film coating a surface of said lead base material and including at least a first layer constituted of a material substantially Pb-free and predominantly composed of tin, wherein said first layer in said metal thin film has an amorphous structure.

8. The electronic component as recited in claim 7 , wherein said first layer is constituted substantially of pure tin, or a tin-based alloy predominantly composed of tin and containing as an additive metal at least one out of the group consisting of bismuth, silver, copper, indium and zinc.

9. The electronic component as recited in claim 1 , wherein said first layer is constituted substantially of pure tin, and an average crystal size index of said first layer is in a range of 7 to 20.

10. The electronic component as recited in claim 1 , wherein said first layer includes a tin-bismuth alloy predominantly composed of tin and containing not less than 0.5 wt % but not more than 4 wt % of bismuth, and an average crystal size index of said first layer is in a range of 7 to 20.

11. The electronic component as recited in claim 1 , wherein said first layer includes a tin-silver alloy containing not less than 0.5 wt % but not more than 6 wt % of silver, and an average crystal size index of said first layer is in a range of 7 to 20.

12. The electronic component as recited in claim 1 , wherein said first layer includes a tin-copper alloy containing not more than 3 wt % of copper, and an average crystal size index of said first layer is in a range of 10 to 30.

13. The electronic component as recited in claim 1 , wherein said metal material is either a metal predominantly composed of copper, or an iron-nickel alloy.

14. A method of manufacturing an electronic component comprising an external terminal, including a lead base material constituted of a predetermined metal material and a metal thin film coating a surface of said lead base material, said metal thin film including at least a first layer constituted of a material substantially Pb-free and predominantly composed of tin, said first layer being formed by an electrolytic plating process,

wherein said electrolytic plating process for forming said first layer includes an initial plating step of supplying a current having a current density not greater than 1 A/dm 2 during an initial stage of a predetermined duration of time.

15. The method as recited in claim 14 , further comprising a heat treatment step of heating said first layer at a predetermined temperature for a predetermined time after said plating process,

wherein said predetermined temperature in said heat treatment step is not more than a melting point of said first layer.

16. The method as recited in claim 14 , further comprising a heat treatment step of heating said first layer at a predetermined temperature for a predetermined time after said plating process,

wherein said heat treatment step includes melting step of heating said first layer at a temperature equal to or higher than a melting point thereof for a predetermined time and gradual cooling step of gradually cooling said first layer after said melting step, and

wherein a cooling rate in said gradual cooling step is not more than 3 degree centigrade per second.