Semiconductor device with joint structure having lead-free solder layer over nickel layer

1. A semiconductor device comprising a joint structure having a copper underlying conductive layer, a nickel jointing layer formed on the copper underlying conductive layer, a Pb-free solder layer formed over the nickel jointing layer, and a tin-based alloy layer comprising elements of these layers formed between the nickel jointing layer and the Pb-free solder layer;

wherein sulfur concentration in the nickel jointing layer is less than 1% as the ratio of the sulfur ion number to the ion count number of the jointing layer in secondary ion mass spectrometry so that an impact bending strain exceeds 2000 ppm.

2. The semiconductor device according to claim 1 , wherein the nickel jointing layer is a plating layer made mainly of nickel and phosphorus.

3. The semiconductor device according to claim 1 , wherein the Pb-free solder layer is a bump.

4. The semiconductor device according to claim 1 ,

wherein the copper underlying conductive layer is an electrode pad of a wiring board,

wherein the nickel jointing layer is a plating layer formed on the surface of the electrode pad, and

wherein the Pb-free solder layer is a bump jointed to the jointing layer.

5. The semiconductor device according to claim 1 ,

further comprising a wiring board in which an electrode pad is formed on its rear face opposite to its main face, and a semiconductor chip mounted on the main face of the wiring board,

wherein the copper underlying conductive layer is an electrode pad of the wiring board,

wherein the nickel jointing layer is a plating layer formed on the surface of the electrode pad, and

wherein the Pb-free solder layer is a bump jointed to the jointing layer.