LEAD-FREE SOLDER

• US 20120111924A1
• Filed: 01/18/2012
• Published: 05/10/2012
• Est. Priority Date: 08/05/2005
• Status: Abandoned Application

• Current Assignee: Fuji Electric Device Technology Company Limited (Fuji Electric Systems Company Limited), Makoto Asami
• Original Assignee: Fuji Electric Systems Company Limited
• Inventors: MAKITA, Kazuyuki, ICHINOSE, Masaki, WATASHIMA, Taketo, SOUTOME, Masayuki, YAMASHITA, Mitsuo, ASAGI, Takeshi, HIRAI, Masatoshi, MURATA, Toru
• Application Number:
  US13/352,984
• Publication Number:
  US 20120111924A1
• Time in Patent Office: Days
• US Class Current: 228/121
• CPC Class Codes: B23K 35/262 Sn as the principal constituent
• CPC Class Codes: Y10T 428/31678 Of metal

Abstract

According to one embodiment of the invention, there is provided a lead-free solder including an alloy rolled into a shape of sheet. The alloy includes: tin; from 10 wt % to less than 25 wt % of silver; and from 3 wt % to 5 wt % of copper. The alloy is free from lead.

Claims

1. A method of manufacturing a stacked wafer structure with a lead-free solder, said method comprising:

alloying tin, silver at a range of 10-25% by weight, and copper at a range of 3-5% by weight, to obtain a lead-free alloy ingot;

rolling said lead-free alloy ingot into a shape of a sheet to obtain a lead-free solder;

stacking a plurality of semiconductor wafer and lead free solder alternatively to obtain a stacked wafer solder structure; and

heating the stacked wafer solder structure at a joining temperature ranging from a temperature that is higher than a temperature of the solidus line of the solder by 30°

C. to a temperature that is lower than a temperature of the liquidus line of the solder by 30°

C. under pressure to melt the lead free solder and obtain the stacked wafer structure.

2. The method according to claim 1, wherein the range of silver in the alloying step is 10%-20% by weight.

3. The method according to claim 1, wherein the lead-free solder has a thickness ranging from 40 μ

m to 120 μ

m.

4. The method according to claim 1, wherein the lead-free solder is Sn-10Ag-5Cu solder with 10 wt % Ag and wt % Cu, and the lead-free solder has a solidus temperature of 227.5°

C. and a liquidus temperature of 355°

C.

5. The method according to claim 1, wherein the lead-free solder is Sn-15Ag-5Cu solder with 15 wt % Ag and 5 wt % Cu, and the lead-free solder has a solidus temperature of 227.5°

C. and a liquidus temperature of 363°

C.

6. The method according to claim 1, wherein the lead-free solder is Sn-20Ag-3Cu solder with 20 wt % Ag and wt % Cu, and the lead-free solder has a solidus temperature of 227.5°

C. and a liquidus temperature of 364°

C.

7. The method according to claim 1, wherein the lead-free solder is Sn-20Ag-5Cu solder with 20 wt % Ag and wt % Cu, and the lead-free solder has a solidus temperature of 227.5°

C. and a liquidus temperature of 366°

C.