REDUCING JOINT EMBRITTLEMENT IN LEAD-FREE SOLDERING PROCESSES

• US 20080160310A1
• Filed: 02/25/2008
• Published: 07/03/2008
• Est. Priority Date: 08/24/2005
• Status: Active Grant

• Current Assignee: Alpha Assembly Solutions Inc. (Element Solutions Inc)
• Original Assignee: Fry's Metals Incorporated (Element Solutions Inc)
• Inventors: Laughlin, John, Pandher, Ranjit, Singh, Bawa, Lewis, Brian G.
• Granted Patent: US 8,191,757 B2
• Time in Patent Office: Days
• US Class Current: 428/403
• CPC Class Codes: B23K 35/262 Sn as the principal constituent
• CPC Class Codes: H05K 1/09 Use of materials for the conductive, e.g. metallic pattern
• CPC Class Codes: H05K 2201/0355 Metal foils
• CPC Class Codes: H05K 3/244 Finish plating of conductors, especially of copper conductors, e.g. for pads or lands selective plating methods H05K3/243; finish plating of conductors made by printing techniques H05K3/246; solder as finish H05K3/3457, e.g. by plating H05K3/3473
• CPC Class Codes: H05K 3/3463 Solder compositions in relation to features of the printed circuit board or the mounting process
• CPC Class Codes: Y10T 428/2991 Coated

Abstract

In the manufacture of products such as printed wiring boards or chip scale packaging and ball grid arrays, incorporating one or more elements selected from among Ni, Co, Cr, Mn, Zr, Fe and Si into a lead-free soldering process to reduce joint embrittlement. In varied embodiments this is accomplished by spraying onto a solder sphere or preform surface, by spraying onto a device substrate surface, or by incorporating into the device substrate alloy.

Claims

1. A method of forming a solder joint, comprising:

(a) providing a lead-free, tin-containing solder alloy;

(b) providing a printed wiring board substrate or a ball grid array substrate, said substrate being formed from a material comprising copper, optionally also zinc, and one or more of Ni, Co, Cr, Mn, Zr, Fe and Si and/or alloys thereof;

(c) heating the solder alloy; and

(d) either before, during or after step (c) contacting the solder alloy with the substrate.

2. The method of claim 1 wherein said material of the substrate comprises 95 wt % or more Cu and at least one selected from among 0.04 to 5 wt % Zr, 0.04 to 5 wt % Fe, and 0.04 to 5 wt % Si.

3. A method of forming a solder joint, comprising:

(a) providing a lead-free, tin-containing solder alloy;

(b) providing a printed wiring board substrate or a ball grid array substrate, said substrate being formed from a material comprising copper and optionally also zinc;

(c) depositing one or more of Ni, Co, Cr, Mn, Zr, Fe and Si and/or alloys thereof on a surface of the substrate;

(d) heating the solder alloy; and

(e) either before, during or after step (d) contacting the solder alloy with said surface of the substrate.

4. A method as claimed in claim 3, wherein the step of depositing one or more of Ni, Co, Cr, Mn, Zr, Fe and Si and/or an alloy thereof on said surface of the substrate is achieved by plating, spraying and/or vapour deposition.

5. A method as claimed in claim 4, wherein the spraying comprises plasma, arc or flame spraying.

6. A method as claimed in claim 4, wherein the vapour deposition comprises chemical vapour deposition or evaporation, sputtering or ion implantation.

7. A method of forming a solder joint, comprising:

(a) providing a lead-free, tin-containing solder alloy;

(b) forming the solder alloy into spheres or other preforms;

(c) depositing on the surface of the spheres or other preforms one or more of Ni, Co, Cr, Mn, Zr, Fe and Si and/or an alloy thereof;

(d) providing a printed wiring board substrate or a ball grid array substrate, said substrate being formed from a material comprising copper and optionally also zinc;

(e) heating the solder alloy spheres or other preforms; and

(f) either before, during or after step (e) contacting the solder alloy with said surface of the substrate.

8. A method as claimed in claim 7, wherein the step of depositing one or more of Ni, Co, Cr, Mn, Zr, Fe and Si and/or an alloy thereof on the surface of the spheres or other preforms is achieved by plating, spraying and/or vapour deposition.

9. A method as claimed in claim 8, wherein the spraying comprises plasma, arc or flame spraying.

10. A method as claimed in claim 8, wherein the vapour deposition comprises chemical vapour deposition or evaporation, sputtering or ion implantation.

11. A method as claimed in claim 7 wherein the one or more of Ni, Co, Cr, Mn, Zr, Fe and Si and/or an alloy thereof is/are incorporated into the solder joint.

12. A method as claimed in claim 7, wherein the lead-free, tin-containing solder alloy is also essentially free of one or more of Ni, Co, Cr. Mn, Zr, Fe and Si.

13. A method as claimed in claim 7 wherein the substrate is formed from one of the following alloy compositions (wt. %):

Cu-1Zr, Cu-2.35Fe-0.03P-0.12Zn, Cu-1.5Fe-0.18P-0.8Co-0.6Sn, Cu-0.6Fe-0.2P-0.05Mg, Cu-2.8Al-1.8Si-0.4Co, Cu-3.0Ni-0.65Si-0.15Mg, Cu-3.0Si-1.5Sn-0.1Cr.

14. A method as claimed in claim 7, wherein the substrate comprises an electrodeposited foil or a rolled foil bonded to another material.

15. A method as claimed in claim 7, wherein the substrate further comprises a solderability enhancing coating.

16. A method as claimed in claim 15, wherein the solderability enhancing coating comprises one or more of tin, gold and/or silver, including alloys thereof, or an organic coating.

17. A method as claimed in claim 7, wherein the lead-free, tin-containing solder alloy also comprises Cu and/or Ag.

18. A lead-free, tin-containing solder alloy in the form of spheres or preforms, wherein an outer surface of the spheres or performs has deposited thereon one or more of Ni, Co, Cr, Mn, Zr, Fe and Si and/or an alloy of any one or more thereof.

19. A lead-free, tin-containing solder alloy as claimed in claim 18, wherein a subsurface centre portion of the spheres or preforms is essentially free of one or more of Ni, Co, Cr, Mn, Zr, Fe and Si.

20. A lead-free, tin-containing solder alloy as claimed in claim 18, wherein the concentration of one or more of Ni, Co, Cr, Mn, Zr, Fe and Si is highest at the surface.