Pb-free solder-connected structure and electronic device
Provided are a bonded structure by a lead-free solder and an electronic article comprising the bonded structure. The bonded structure has a stable bonding interface with respect to a change in process of time, an enough strength and resistance to occurrence of whiskers while keeping good wettability of the solder. In the bonded structure, a lead-free Sn—Ag—Bi alloy solder is applied to an electrode through an Sn—Bi alloy layer. The Sn—Bi alloy, preferably, comprises 1 to 20 wt % Bi in order to obtain good wettability of the solder. In order to obtain desirable bonding characteristics having higher reliability in the invention, a copper layer is provided under the Sn—Bi alloy layer thereby obtaining an enough bonding strength.
1. A semiconductor device to be mounted on a substrate via a Pb-free solder, comprising:
a lead; and
a Bi-containing layer formed on the lead and constituted by an alloy consisting essentially of Sn and Bi,
wherein a contained amount of Bi in the alloy is greater than or equal to 1 wt %, and less than or equal to 5 wt %; and
wherein the Bi-containing layer is a layer separate from the Pb-free solder.
2. The semiconductor device according to claim 1 , wherein the lead is comprised of a Cu alloy.
3. The semiconductor device according to claim 1 , wherein the lead is comprised of a Fe—Ni alloy.
4. The semiconductor device according to claim 1 , wherein the semiconductor device is a Thin Small Outline Package (TSOP).
5. The semiconductor device according to claim 1 , wherein the semiconductor device is a Quad Flat Package (QFP).
6. The semiconductor device according to claim 1 , wherein the Bi-containing layer is formed directly on the lead.
7. The semiconductor device according to claim 3 , wherein a Cu layer is formed between the lead and the Bi-containing layer.
8. The semiconductor device according to claim 1 , wherein the lead contains Cu.
9. The semiconductor device according to claim 1 , wherein the Bi-containing layer is a layer in addition to the Pb-free solder.
10. The semiconductor device according to claim 1 , which additionally includes a Pb-free solder, the Bi-containing layer being provided between the lead and the Pb-free solder.
11. The semiconductor device according to claim 1 , wherein the Bi-containing layer is a layer that improves wettability of the Pb-free solder to the lead.