SOLDERING METHOD AND RELATED DEVICE FOR IMPROVED RESISTANCE TO BRITTLE FRACTURE
A lead-free solder joint is formed between a tin-silver-copper solder alloy (SAC), SACX, or other commonly used Pb-free solder alloys, and a metallization layer of a substrate. Interaction of the SAC with the metallization layer forms an intermetallic compound (IMC) that binds the solder mass to the metallization layer. The IMC region is substantially free of any phosphorous-containing layers or regions.
1 . A soldering method comprising:
providing a substrate comprising a core layer and at least a nickel layer disposed over at least a portion of the core layer, the nickel layer having no more than a predetermined amount of phosphorus, the predetermined amount adapted to prevent the formation of an effective nickel-phosphorus layer;
contacting together the substrate and a solder mass; and
heating the solder mass to a temperature that is at least a melting point temperature of the solder mass to form an intermetallic compound region that couples the solder mass to the nickel layer;
wherein the predetermined amount of phosphorus is controlled as a function of an expected size of the solder mass.
2 . The method of claim 1 wherein the substrate further comprises a gold layer disposed over at least a portion of the nickel layer, the gold layer having no more than another predetermined amount of phosphorus to prevent the formation of the effective nickel-phosphorus layer.
3 . The method of claim 2 wherein providing the substrate comprises employing an electroplating procedure to electroplate the gold layer over the nickel layer, the electroplating procedure utilizing an electroplating bath that is substantially free of phosphorus.
4 . The method of claim 2 wherein the gold layer is substantially free of phosphorus.
5 . The method of any one of claim 1 wherein the solder mass comprises at least 90% tin by weight.
6 . The method of claim 5 wherein the temperature is at least 230° C.
7 . The method of claim 5 wherein the intermetallic compound region comprises an alloy of nickel and tin, an alloy of nickel, copper and tin, or an alloy of nickel, copper, gold and tin.
8 . The method of claim 1 wherein providing the substrate comprises employing an electroplating procedure to electroplate the nickel layer over the core layer, the electroplating procedure utilizing an electroplating bath that is substantially free of phosphorus.
9 . The method of claim 8 wherein the substrate further comprises a copper layer disposed between the core layer and the nickel layer, and the nickel layer is electroplated onto the copper layer.
10 . The method of claim 1 wherein the intermetallic compound region is devoid of any phosphorus-containing layers thicker than 0.150 μm, and is free of any phosphorus-containing regions in excess of 25% of the surface area of the intermetallic compound region and thicker than 0.150 μm.
11 . The method of claim 1 wherein the intermetallic compound region is devoid of a nickel-phosphorus layer or region having an effective thickness in excess of about 1500 Å.
12 . The method of claim 1 wherein the intermetallic compound region is devoid of a nickel-phosphorus layer or region having an effective thickness in excess of 150 Å.
13 . The method of claim 1 wherein the intermetallic compound region is devoid of a nickel-phosphorus layer or region having an effective thickness in excess of 10 Å.
14 . A soldering method comprising:
providing a first electrical component comprising a nickel layer, the nickel layer having no more than a predetermined amount of phosphorus, the predetermined amount adapted to prevent the formation of an effective nickel-phosphorus layer;
providing a second electrical component having an electrical contact;
contacting a solder mass to the first electrical component and the electrical contact; and
heating the solder mass to a temperature that is at least a melting point temperature of the solder mass to form an intermetallic compound region that couples the solder mass to the nickel layer and that couples the solder mass to the electrical contact;
wherein the predetermined amount of phosphorus is controlled as a function of an expected size of the solder mass.
15 . The method of claim 14 wherein the nickel layer is disposed within a through hole of a circuit board.
16 . The method of claim 14 wherein the nickel layer is disposed over a pad on the circuit board.
17 . The method of claim 14 wherein the first electrical component is a circuit board and the second electrical component is a ball grid array device.
18 . The method of claim 14 wherein the first electrical component is a circuit board and the second electrical component is a flip-chip device.
19 . The method of claim 14 wherein the first electrical component is a flip-chip device and the second electrical component is a flip-chip device.
20 . The method of claim 14 , wherein the intermetallic compound region is devoid of any phosphorus-containing layers thicker than 0.150 μm, and is free of any phosphorus-containing regions in excess of 25% of the surface area of the intermetallic compound region and thicker than 0.150 μm.