[0001] This invention relates to Electronic solder materials. To be more specific, this invention pertains to lead free solder alloy for high temperature applications.
RELATED ART
[0002] Lead-Tin alloy was considerable best available composition (63Sn-37Pb) for solder alloy in the electronics package industry. It has low melting point, good hardness, strength, wetting properties and low cost. Lead containing solder were used for more than 2000 years. The lead is not environment friendly due to its . inherent toxicity. If one incurs chronic exposure to lead, it could possibly result in an accumulation of lead in the human body, which may cause damage to the blood and central nervous systems, the pioneer segment of human body. Contamination of ground" water and soil caused by electronic scrap is a heavy risk.
[0003] Environmental friendly legislation put forward by, European Union (EU), Waste of Electronic and Electrical equipment (WEEE), Restriction of hazardous Substances (RoHS) etc., led to ban of using lead in electronic assemblies. Countries like Japan,China, Korea, South Africa followed this legislation in their respective countries.
[0004] As a result of the ban on Lead, researchers around the world were searching for new lead free solder alloy which can replace the Sn-Pb alloy. There are some requirements that should be satisfied in order to choose the alloy for solder joint making. The melting point of the solder alloy should be low such that the heat required for joining should not cause any damage to the electronic assembly. This is an important property because even if the solder alloy possesses good reliability and low cost, if the melting temperature is high, then it cannot be used for solder joint applications. The wetting property is another requirement, since the wetting and joining is the principle behind the solder joint formation, contact angle should be low. Tendency of a liquid metal to spread over a solid surface is termed as wettability property. Another property is the availability of the
_ candidate metals. Cost is an important factor that needs to be
F l-L t LHtNNAl 1 7 / 0 / / 2 6 1 9 15= 89

considered while selecting a lead free solder alloy along with their properties
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[0005] Many new lead free solder alloys were introduced into the market as a result of the works from various researchers. None of them have perfectly all the good properties. Most of the lead free solder alloys cannot be used for high temperature applications like automobile electronic packaging. Even if some candidates withstand temperature, they will fail at another properties.
SUMMARY
[0006] A lead-free solder alloy for high temperature applications is provided, which has, by weight, at least 95.5 % Tin, 1.4-1.5% Copper, 1.4-1.5% Nickel and 1.4-1.5% Silver.
[0007] A method also is provided which includes the steps of melting a solder alloy to produce a molten alloy, contacting the molten alloy with at least one solid metal piece, and causing or permitting.the molten alloy to cool and harden to thereby provide a solder joint. The solder alloy has, by weight, at least 95.5 % Tin, 1.4-1.5% Copper, 1.4-1.5% Nickel and 1.4-1.5% Silver.
[0008] A solder joint is provided which has a melting point in the range (240-250 degree Celsius).The solder alloy has, by weight, at least 95.5 % Tin,1.4-1.5% Copper, 1.4-1.5% Nickel and 1.4-1.5% Silver.
[0009] Several aspects are described below, with reference to diagrams. It should be understood that numerous specific details, relationships, and methods are set forth to provide a full understanding of the present disclosure. One who skilled in the relevant art, however, will readily recognize that the present disclosure can be practiced without one or more of the specific details, or with other methods, etc. In other instances, well-known structures or operations are not shown in detail to avoid obscuring the features of the present disclosure.
BRIEF DESCRIPTION OF DRAWINGS
[0010] FIG.l FE-SEM image of the surface of the lead free solder alloy at 100 KX.

[0011] A lead-free solder alloy discussed herein exhibits good brightness, comparatively high reflective appearance, yet it contains no or Substantially no lead, except for potential trace quantities of lead that may be present as an impurity in the alloy components. The solder alloy discussed here contains Tin as the base materials with small amounts of copper, nickel and silver, at least by weight, 95.5 % Tin, 1.4-1.5% Copper, 1.4-1.5% Nickel and 1.4-1.5% Silver.
[0012] The chemical composition analysis shows the following results in weight %: Tin- 95.5136, Copper- 1.4326, Nickel-1.4882 and Silver-1.4932. the rest 0.0724% will be impurities.
[0013] Hardness test of the alloy reveals that it has a hardness of 24.2 Hv. Good wettability characteristics were also found.
[0014] Melting temperature analysis shows that the alloy has melting point of 242 degree Celsius.
[0015] By comparing this lead free solder alloy with the existing lead free solder alloys in the market, the new new lead free solder alloy with at least by weight, 95.5 % Tin,1.4-1.5% Copper, 1.4-1.5% Nickel and 1.4-1.5% Silver is found to be having significantly best properties and shows good properties at high temperatures.
[0016] While various embodiment of the present disclosure have been described above, it should be understood that they have been presented by way of example only, and not limitation. Thus, the breadth and scope of the present disclosure should not be limited by any of the above-discussed embodiment, but should be defined only in accordance with the following claims and their equivalents
[0017] While various embodiments of the present disclosure have been described above, it should be understood that they have been presented by way of example only, and not limitation. Thus, the breadth and scope of the present disclosure should not be limited by any of the above-discussed embodiments, but should be defined only in accordance with the following claims and their equivalents.