Auto-regulating solder composition

• US 5,573,859 A
• Filed: 09/05/1995
• Issued: 11/12/1996
• Est. Priority Date: 09/05/1995
• Status: Expired due to Fees

• Current Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Suppelsa, Anthony B.
• Primary Examiner(s): Mai, Ngoclan
• Assistant Examiner(s): CHI, ANTHONY
• Application Number:
  US08/523,449
• Time in Patent Office: 434 Days
• Field of Search: 428/548, 428/553, 428/56.3
• US Class Current: 428/553
• CPC Class Codes: B22F 1/17 Metallic particles coated with metal
• CPC Class Codes: B23K 35/0244 Powders, particles or spheres; Preforms made therefrom
• CPC Class Codes: B23K 35/025 Pastes, creams, slurries
• CPC Class Codes: H05K 2201/0215 Metallic fillers
• CPC Class Codes: H05K 2201/0218 Composite particles, i.e. first metal coated with second metal
• CPC Class Codes: H05K 2201/083 Magnetic materials
• CPC Class Codes: H05K 2203/101 Using electrical induction, e.g. for heating during soldering
• CPC Class Codes: H05K 2203/104 Using magnetic force, e.g. to align particles or for a temporary connection during processing
• CPC Class Codes: H05K 3/3463 Solder compositions in relation to features of the printed circuit board or the mounting process
• CPC Class Codes: H05K 3/3485 Applying solder paste, slurry or powder thick film methods for applying conductive paste or ink patterns H05K3/12
• CPC Class Codes: H05K 3/3494 Heating methods for reflowing of solder using integral heating means H05K1/0212
• CPC Class Codes: Y10T 428/12028 Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, etc.]
• CPC Class Codes: Y10T 428/12063 Nonparticulate metal component
• CPC Class Codes: Y10T 428/12132 Next to Fe-containing particles

Abstract

A soldering composition is self melting and is auto-regulating. The solder composition (100) has a central core (102) made from a non-magnetic metal. A coating (105) of a magnetic material surrounds most or all of the central core. A solder layer (108) overlies the coating of magnetic material, and the solder layer has a melting temperature that is lower than the Curie temperature of the magnetic material. The auto-regulating temperature substantially corresponds to the Curie temperature. When the solder composition is placed in a field of alternating current, the magnetic material heats up and melts the solder coating. When the Curie temperature is reached, the magnetic material stops heating, thus controlling the maximum temperature of the soldering composition. As the temperature of the composition drops below the Curie temperature, the magnetic material again heats up, thus keeping the temperature of the solder constant.

Claims

1. A soldering composition having an auto-regulating temperature, comprising:

a central core of a non-magnetic metal;

a magnetic material coating the central core, the magnetic material having a Curie temperature substantially corresponding to the auto-regulating temperature; and

a solder layer overlying the magnetic material, the solder layer having a melting temperature that is lower than the Curie temperature.

2. The soldering composition as described in claim 1, wherein the central core has a melting temperature greater than the Curie temperature.

3. The soldering composition as described in claim 1, wherein the Curie temperature is about 1 degree-100 degrees C. greater than the melting temperature of the solder layer.

4. The soldering composition as described in claim 1, wherein the soldering composition is heated to the melting point of the solder by applying an alternating current field of substantially constant amplitude to the magnetic material sufficient to cause the magnetic material to reach the Curie temperature.

5. The soldering composition as described in claim 1, wherein the central core comprises one or more metals or metal alloys selected from the group consisting of elements from Groups IVb, Vb, VIb, VIIb, VIII, Ib, IIb, IIIa, IVa and Va.

6. The soldering composition as described in claim 1, wherein the magnetic material comprises one or more metal alloys selected from the group consisting of type 304 austenitic stainless steel, INCONEL®

type 718, and alloy type 95.

7. The soldering composition as described in claim 1, wherein the magnetic material is a ferromagnetic material.

8. The soldering composition as described in claim 1, wherein the solder layer comprises one or more metals or metal alloys selected from the group consisting of In, Pb, Sn, Bi, Sb, Au and Ag.

9. The soldering composition as described in claim 1, wherein the magnetic material is electrically conductive.

10. The soldering composition as described in claim 1, wherein the soldering composition comprises solder particles.

11. The soldering composition as described in claim 10, further comprising a vehicle and a solder flux blended with the solder particles.

12. A soldering composition, comprising:

a vehicle and a flux; and

first solder particles comprising;

a central core of a non-magnetic metal;

a magnetic material coating the central core, the magnetic material having a Curie temperature substantially corresponding to the auto-regulating temperature; and

a solder layer overlying the magnetic material, the solder layer having a melting temperature that is lower than the Curie temperature.

13. The soldering composition as described in claim 12, further comprising second solder particles comprising an alloy of tin and lead.

14. The soldering composition as described in claim 12, wherein the application of an alternating current field of substantially constant amplitude to the magnetic material causes the magnetic material to heat until it reaches the Curie temperature, thereby melting the solder layer.

15. The soldering composition as described in claim 14, wherein the continued application of the alternating current field does not further heat the magnetic layer.