Lead-free solder paste

Patent metadata

Field	Value
Publication number	US-9770786-B2
Application number	US-201013261530-A
Country	US
Kind code	B2
Filing date	Jun 1, 2010
Priority date	Jun 1, 2010
Publication date	Sep 26, 2017
Grant date	Sep 26, 2017

Abstract

As electronic equipment has become smaller in size, printed circuit boards which cannot be subjected to cleaning have been developed, and a no-clean lead-free solder paste is becoming necessary. In order for a solder paste not to require cleaning, it is necessary that the color of the residue be transparent and that the residue be non-tacky. A maleated rosin, which is a rosin suited for no-clean paste, has a high acid value so it is not suitable for a flux for lead-free solder. As a means of suppressing a reaction between a flux containing a maleated rosin and a Sn—Ag—Cu based solder alloy powder, a Sn—Ag—Cu—Sb based solder alloy powder is used which adds 1-8 mass % of Sb to a Sn—Ag—Cu based solder alloy. As a result, it is possible to provide a solder paste which has the excellent effect that the solder paste does not easily undergo changes over time and has a long pot life.

First claim

The invention claimed is:

1. A lead-free solder paste comprising:
a solder alloy powder of a solder alloy consisting of 1.0-4.0 mass % of Ag, 0.4-1 mass % of Cu, 1-8 mass % of Sb, and a balance of Sn; and
a flux which contains one or more rosins which collectively are the largest component of the flux in mass %, the flux containing 5-45 mass % of a maleated rosin.

2. A lead-free solder paste as claimed in claim 1 wherein the solder alloy powder contains 2-5 mass % of Sb.

3. A lead-free solder paste as claimed in claim 1 which has an increase in viscosity at 60 days at 25° C. after preparation of the solder paste with respect to its viscosity one day after preparation of at most 25%.

4. A lead-free solder paste as claimed in claim 1 wherein the flux consists of one or more rosins and at least one material selected from an activator, a thixotropic agent, and a solvent.

5. A lead-free solder paste as claimed in claim 4 wherein the flux contains a total of at least 50 mass % of the one or more rosins.

6. A lead-free solder paste as claimed in claim 1 wherein the flux contains at least one rosin selected from a polymerized rosin, a hydrogenated rosin, and a phenol modified rosin.

7. A lead-free solder paste as claimed in claim 1 wherein the flux contains a hydrogenated rosin.

8. A lead-free solder paste as claimed in claim 1 which consists of the solder alloy powder and the flux.

9. A lead-free solder paste comprising:
a solder alloy powder of a solder alloy consisting of 1.0-4.0 mass % of Ag, 0.4-1.0 mass % of Cu, 1-8 mass % of Sb, at least one of Ni, Co, and Fe in a total amount of greater than 0 to at most 0.5 mass %, and a balance of Sn; and
a flux which contains one or more rosins which collectively are the largest component of the flux in mass %, the flux containing 5-45 mass % of a maleated rosin.

Assignees

• Toyoda Yoshitaka
• Imai Fumihiro
• Senju Metal Industry Co

Inventors

• Toyoda Yoshitaka
• Imai Fumihiro

Classifications

• H05K3/346

  Solder materials or compositions specially adapted therefor · CPC title

• B23K35/3612

  with organic compounds as principal constituents · CPC title

• B23K35/3616

  Halogen compounds · CPC title

• H05K3/3489

  Composition of fluxes; Application thereof; Other processes of activating the contact surfaces · CPC title

• H05K3/3463

  Electricity · mapped topic