LOW TEMPERATURE SOLDERING SOLUTIONS FOR POLYMER SUBSTRATES, PRINTED CIRCUIT BOARDS AND OTHER JOINING APPLICATIONS

Abstract

A solder alloy comprising: from 40 to 65 wt. % bismuth; from I to IO wt. % indium; at least one of: from 0.1 to 5 wt. % gallium, from 0.1 to 5 wt. % zinc, from 0.1 to 2 wt. % copper, from 0.01 to 0.1 wt. % cobalt, from 0.1 to 2 wt. % silver, from 0.005 to 0.05 wt. % titanium, and from 0.01 to 1 wt. % nickel; optionally up to 1 wt. % of one or more of: vanadium, rare earth metals, neodymium, chromium, iron, aluminium, phosphorus, gold, tellurium, selenium, calcium, vanadium, molybdenum, platinum, magnesium, silicon, and manganese; and the balance tin together with any unavoidable impurities.

Claims

1. A solder alloy comprising: from 40 to 65 wt. % bismuth; from 1 to 10 wt. % indium; at least one of: from 0.1 to 5 wt. % gallium, from 0.1 to 5 wt. % zinc, from 0.1 to 2 wt. % copper, from 0.01 to 0.1 wt. % cobalt, from 0.1 to 2 wt. % silver, from 0.005 to 0.05 wt. % titanium, and from 0.01 to 1 wt. % nickel; optionally one or more of: up to 1 wt. % vanadium, up to 1 wt. % rare earth metals, up to 1 wt. % neodymium, up to 1 wt. % chromium, up to 1 wt. % iron, up to 1 wt. % aluminium, up to 1 wt. % phosphorus, up to 1 wt. % gold, up to 1 wt. % tellurium, up to 1 wt. % selenium, up to 1 wt. % calcium, up to 1 wt. % vanadium, up to 1 wt. % molybdenum, up to 1 wt. % platinum, up to 1 wt. % magnesium, up to 1 wt. % silicon, and up to 1 wt. % manganese; and the balance tin together with any unavoidable impurities.

2. The solder alloy of claim 1, wherein the solder alloy comprises from 42 to 60 wt. % bismuth, preferably from 45 to 59 wt. % bismuth, more preferably from 47 to 58.5 wt. % bismuth, even more preferably from 50 to 58 wt. % bismuth, still even more preferably from 55 to 57.5 wt. % bismuth; and/or wherein the solder alloy comprises from 1.5 to 9 wt. % indium, preferably from 2 to 8 wt. % indium, more preferably from 3 to 7 wt. % indium; and/or wherein the solder alloy comprises from 0.5 to 4 wt. % gallium, more preferably from 1 to 3 wt. % gallium; and/or wherein the solder alloy comprises from 0.5 to 4 wt. % zinc, more preferably from 1 to 3 wt. % zinc; and/or wherein the solder alloy comprises from 0.15 to 1.5 wt. % copper, preferably from 0.18 to 0.32 wt. % copper; and/or wherein the solder alloy comprises from 0.02 to 0.09 wt. % cobalt, preferably from 0.03 to 0.08 wt. % cobalt; and/or wherein the solder alloy comprises from 0.2 to 1.5 wt. % silver, preferably from 0.3 to 1.2 wt. % silver; and/or wherein the solder alloy comprises from 0.055 to 0.045 wt. % titanium, preferably from 0.01 to 0.04 wt. % titanium; and/or wherein the solder alloy comprises 0.02 to 0.9 wt. % nickel, preferably from 0.025 to 0.8 wt. % nickel, more preferably from 0.03 to 0.5 wt. % nickel.

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11. The solder alloy of claim 1, wherein the solder alloy comprises: from 0.001 to 1 wt. % vanadium, preferably from 0.01 to 0.5 wt. % vanadium, more preferably from 0.1 to 0.3 wt. % vanadium; and/or from 0.001 to 1 wt. % rare earth metals, preferably from 0.01 to 0.5 wt. % rare earth metals, more preferably from 0.1 to 0.3 wt. % rare earth metals; and/or from 0.001 to 1 wt. % neodymium, preferably from 0.01 to 0.5 wt. % neodymium, more preferably from 0.1 to 0.3 wt. % neodymium; and/or from 0.001 to 1 wt. % chromium, preferably from 0.01 to 0.5 wt. % chromium, more preferably from 0.1 to 0.3 wt. % chromium; and/or from 0.001 to 1 wt. % iron, preferably from 0.01 to 0.5 wt. % iron, more preferably from 0.1 to 0.3 wt. % iron; and/or from 0.001 to 1 wt. % aluminium, preferably from 0.01 to 0.5 wt. % aluminium, more preferably from 0.1 to 0.3 wt. % aluminium; and/or from 0.001 to 1 wt. % phosphorus, preferably from 0.01 to 0.5 wt. % phosphorus, more preferably from 0.1 to 0.3 wt. % phosphorus; and/or from 0.001 to 1 wt. % gold, preferably from 0.01 to 0.5 wt. % gold, more preferably from 0.1 to 0.3 wt. % gold; and/or from 0.001 to 1 wt. % tellurium, preferably from 0.01 to 0.5 wt. % tellurium, more preferably from 0.1 to 0.3 wt. % tellurium; and/or from 0.001 to 1 wt. % selenium, preferably from 0.01 to 0.5 wt. % selenium, more preferably from 0.1 to 0.3 wt. % selenium; and/or from 0.001 to 1 wt. % calcium, preferably from 0.01 to 0.5 wt. % calcium, more preferably from 0.1 to 0.3 wt. % calcium; and/or from 0.001 to 1 wt. % vanadium, preferably from 0.01 to 0.5 wt. % vanadium, more preferably from 0.1 to 0.3 wt. % vanadium; and/or from 0.001 to 1 wt. % molybdenum, preferably from 0.01 to 0.5 wt. % molybdenum, more preferably from 0.1 to 0.3 wt. % molybdenum; and/or from 0.001 to 1 wt. % platinum, preferably from 0.01 to 0.5 wt. % platinum, more preferably from 0.1 to 0.3 wt. % platinum; and/or from 0.001 to 1 wt. % magnesium, preferably from 0.01 to 0.5 wt. % magnesium, more preferably from 0.1 to 0.3 wt. % magnesium; and/or from 0.001 to 1 wt. % silicon, preferably from 0.01 to 0.5 wt. % silicon, more preferably from 0.1 to 0.3 wt. % silicon; and/or from 0.001 to 1 wt. % manganese, preferably from 0.01 to 0.5 wt. % manganese, more preferably from 0.1 to 0.3 wt. % manganese.

12. The solder alloy of claim 1, wherein the solder alloy consists of from 50 to 54 wt. % bismuth, from 4 to 6 wt. % indium, from 0.5 to 1.5 wt. % gallium and the balance tin together with any unavoidable impurities; or wherein the solder alloy consists of from 49 to 53 wt. % bismuth, from 5 to 7 wt. % indium, from 0.5 to 1.5 wt. % gallium and the balance tin together with any unavoidable impurities; or wherein the solder alloy consists of from 49 to 53 wt. % bismuth, from 4 to 6 wt. % indium, from 1.5 to 2.5 wt. % gallium and the balance tin together with any unavoidable impurities; or wherein the solder alloy consists of from 56 to 59 wt. % bismuth, from 0.1 to 0.3 wt. % copper, from 0.02 to 0.04 cobalt from 2 to 4 wt. % indium and the balance tin together with any unavoidable impurities; or wherein the solder alloy consists of from 56 to 59 wt. % bismuth, from 0.1 to 0.3 wt. % copper, from 0.02 to 0.04 cobalt from 4 to 6 wt. % indium, from 1 to 3 wt. % gallium and the balance tin together with any unavoidable impurities; or wherein the solder alloy consists of from 56 to 59 wt. % bismuth, from 0.2 to 0.6 wt. % silver, from 2 to 4 wt. % indium, and the balance tin together with any unavoidable impurities; or wherein the solder alloy consists of from 56 to 59 wt. % bismuth, from 0.2 to 0.6 wt. % silver, from 4 to 6 wt. % indium, from 1 to 3 wt. % gallium and the balance tin together with any unavoidable impurities.

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22. The solder alloy of claim 1, wherein the solder alloy is capable of reflowing at a temperature at least 10° C. lower than tin-bismuth alloy or tin-bismuth-silver eutectic alloy; and/or wherein the solder alloy is in the form of a bar, a stick, a solid or flux cored wire, a foil or strip, a film, a preform, a powder or paste (powder plus flux blend), or solder spheres for use in ball grid array joints or chip scale packages, or other pre-formed solder pieces, with or without a flux core or a flux coating.

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25. A solder paste comprising: the solder alloy of claim 1, and a solder flux.

26. The solder paste of claim 25, wherein the solder flux comprises an activator, wherein the activator comprises an organic acid activator and an organic amine activator, and wherein the molar ratio of organic acid activator to organic amine activator is from 0.8 to 2.5.

27. The solder paste of claim 26, wherein the molar ratio of organic acid activator to organic amine activator is from 1 to 2; and/or wherein the solder flux comprises from 12 to 20 wt. % of the activator based on the total weight of the solder flux.

28. The solder paste of claim 25, wherein the solder paste comprises: from 78 to 92 wt. % of the solder alloy; and from 8 to 22 wt. % of the solder flux.

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30. The solder paste of claim 25, wherein the solder flux comprises one or more of: one or more rosins and/or one or more resins, preferably in an amount of from 25 to 40 wt. %; one or more solvents, preferably in an amount of from 20 to 40 wt. %; one or more additives, preferably in an amount of from 4 to 12 wt. %; one or more rheology modifying agents, preferably in an amount of from 1 to 10 wt. %; and one or more corrosion inhibitors, preferably in an amount of from 0.5 to 3 wt. %.

31. The solder paste of claim 26, wherein: the organic acid activator comprises one or more di-carboxylic acids, one or more mono-carboxylic acids, one or more halo-benzoic acids, and combinations thereof, preferably one or more of phenylsuccinic acid, glutaric acid, adipic acid, suberic acid, sebacic acid, brassylic acid, maleic acid, phenylglutaric acid, dodecandioic acid, diglycolic acid and 2-iodobenzoic acid; and/or the organic amine activator comprises one or more aliphatic- or aromatic-containing primary, secondary or tertiary amines, heterocyclic amines, polyamines solely, and combinations thereof, preferably one or more of benzimidazole, 2-ethylimidazole, diphenylguanidine, triethanolamine, benzotriazole and tolyltriazole.

32. The solder alloy of claim 26, wherein the activator further comprises one or more amino acid activators.

33. The solder alloy of claim 32, wherein the amino acid activator comprises one or more of glutamic acid, aspartic acid, phenylalanine, valine, tyrosine and tryptophan.

34. The solder paste of claim 26, wherein the activator comprises: from 1 to 5 wt. % glutaric acid, from 5 to 12 wt. % adipic acid, from 0 to 2 wt. % 2-iodobenzoic acid, and from 2 to 10 wt. % 2-ethylimidazole.

35. The solder paste of claim 26, wherein the activator comprises: from 7 to 15 wt. % adipic acid, from 0 to 2 wt. % 2-iodobenzoic acid, and from 2 to 10 wt. % 2-ethylimidazole.

36. The solder paste of claim 26, wherein the activator comprises: from 1 to 5 wt. % glutaric acid, from 1 to 10 wt. % glutamic acid, from 3 to 10 wt. % adipic acid, from 0 to 2 wt. % 2-iodobenzoic acid, and from 2 to 10 wt. % 2-ethylimidazole.

37. The solder paste of claim 25, wherein the solder flux comprises: one or more thermoplastic polymers, preferably selected from polyester, polyacrylates and polyphenoxy resins; and/or one or more waxes, preferably selected from vegetable oil waxes and natural waxes; and/or one or more thermoset network forming resins, preferably selected from resins containing polyester or polyacrylate or polyurethane backbones, the product of the reaction of epoxy with hardeners such as amine, acid, anhydrides, the product of the reaction of acid or its derivative with amine, the product of the reaction of acid or its derives with alcohol, the product of the reaction of multiple carbon-carbon bond having allyl, vinyl, methacrylate, methacrylamide functionality, the reaction of hydroxy and isocyanate.

38. The solder paste of claim 25, wherein the solder flux further comprises a corrosion inhibitor, preferably comprising a triazole derivative, more preferably comprising one or more of benzotriazole, tolyltriazole, and carboxybenzotriazole.

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42. Use of a solder alloy of claim 1 in a soldering method.

43. The use according to claim 42, wherein the soldering method is selected from wave soldering, Surface Mount Technology (SMT) soldering, die attach soldering, thermal interface soldering, hand soldering, laser and RF induction soldering, soldering to a solar module, soldering of level 2 LED package boards, and rework soldering.

Description

[0291] The present invention will now be described further, by way of few non-limiting examples of these alloys and a summary of their performance, with reference to the following drawings in which:

[0292] FIG. 1 shows a DSC plot (Heat Flow Q (mW) versus Temperature T (° C.) for the alloy Sn—Bi-6In.

[0293] FIG. 2 shows a DSC plot (Heat Flow Q (mW) versus Temperature T (° C.) for the alloy Sn—Bi-6In-1Ga.

[0294] The present invention will now be described further with reference to the following non-limiting examples.

EXAMPLE 1

[0295] The following solder alloys were prepared: Sn-5Bi-6In and Sn-5Bi-6In-1Ga. As can be seen from FIGS. 1 and 2, the addition of 1% Ga to Sn-5Bi-6In solder reduces the onset temperature of the main melting phase from 118° C. to 110° C. and eliminates phases melting at 78° C. and 100° C. It also introduces a small fraction of another phase melting around 87° C.

[0296] Solder joints were prepared using the two solder alloys. The additional of 1% Ga did not have a significant detrimental effect on the mechanical properties of the solder joint. In Particular, the alloys exhibited similar shear strengths and similar thermal cycling behaviours.

EXAMPLE 2

[0297] A solder alloy was prepared having the following composition:

[0298] (a) from 53 to 54 wt. % of Bi

[0299] (b) from 4 to 5 wt % of In

[0300] (c) 0 to 0.05 wt. % nickel

[0301] (d) the balance tin, together with unavoidable impurities.

[0302] The alloy exhibited a combination of low reflow temperature and favourable mechanical properties.

EXAMPLE 3

[0303] A solder alloy was prepared having the following composition:

[0304] (a) from 55 to 56 wt. % of Bi

[0305] (b) from 2 to 3 wt % of In

[0306] (c) 0 to 0.05 wt. % nickel

[0307] (d) 0.3 to 0.5% Cu

[0308] (e) the balance tin, together with unavoidable impurities.

[0309] The alloy exhibited a combination of low reflow temperature and favourable mechanical properties.

EXAMPLE 4

[0310] A solder alloy was prepared having the following composition:

[0311] (a) from 51 to 53 wt % of In

[0312] (b) 0 to 0.05 wt. % nickel

[0313] (c) 0.3 to 0.5% Cu

[0314] (d) the balance tin, together with unavoidable impurities.

[0315] The alloy exhibited a combination of low reflow temperature and favourable mechanical properties.

EXAMPLE 5

[0316] A solder alloy was prepared having the following composition:

[0317] (a) from 51 to 53 wt % of In

[0318] (b) 0 to 0.05 wt. % nickel

[0319] (c) 0 to 0.05% Ge

[0320] (d) the balance tin, together with unavoidable impurities.

[0321] The alloy exhibited a combination of low reflow temperature and favourable mechanical properties.

EXAMPLE 6

[0322] A solder alloy was prepared having the following composition:

[0323] (a) from 51 to 53 wt % of In

[0324] (b) 0 to 0.05 wt. % nickel

[0325] (c) 0 to 0.03% P

[0326] (d) the balance tin, together with unavoidable impurities.

[0327] The alloy exhibited a combination of low reflow temperature and favourable mechanical properties.

[0328] The foregoing detailed description has been provided by way of explanation and illustration, and is not intended to limit the scope of the appended claims. Many variations in the presently preferred embodiments illustrated herein will be apparent to one of ordinary skill in the art, and remain within the scope of the appended claims and their equivalents.