TECHNOLOGICAL FIELD

The present disclosure generally relates to the field of tin electroplating. More specifically, the present disclosure relates to methods for mitigating tin whisker formation on tin-plated films and tin-plated surfaces by doping the tin with germanium.

BACKGROUND

The worldwide transition to lead-free electronics is forcing most major suppliers of electronic components to convert their product lines from tin/lead-containing finishes to lead-free finishes. As a result, most electronics suppliers have moved to pure electroplated tin finishes. However, there is a tendency of electroplated pure tin finishes to form tin whiskers that extend a distance from the surface. Such tin whiskers have been found to form on a wide variety of tin-plated components, and under a wide range of environmental conditions. Since these tin whiskers are comprised of nearly pure tin and are therefore electrically conductive, they can cause problems, such as, for example, shorting of electronic components. Therefore the growth of tin whiskers from tin-plated surfaces continues to cause reliability and other problems for electronic systems that use components that are plated with tin. Undesirable effects on electronics attributable to tin whisker formation on tin-plated surfaces have caused significant customer dissatisfaction resulting in significant financial impact on the manufacturers of electronics. To date, the only way to ensure that tin whiskers do not grow within an electronic system is to eliminate pure tin from such a system. However, the increasing reliance on the use of tin and tin-plated components in the electronic industry makes this tin elimination strategy unworkable. One tin whisker mitigation strategy has been to immerse all tin-plated component leads into molten tin/lead, from the tip of the lead up to the component body. However, this process can undesirably affect the component and is expensive to implement into the manufacturing process.

BRIEF SUMMARY

According to one variation, the present disclosure relates to a method for mitigating tin whisker growth on a substrate surface. A germanium-containing compound is dissolved to make a germanium-containing solution. Water and a complexing agent are then added to the germanium-containing solution. A water-soluble tin-containing compound is then added to the germanium-containing solution. An optional surfactant/leveling agent may be added before or after the tin-containing compound is added to the germanium-containing solution. Electrodes are immersed into the solution with the electrodes connected to an electrical power source capable of providing an electrical current. The power source is activated to provide the electrical current to the solution resulting in an amount of germanium and tin co-deposited onto the cathodic substrate surface. According to one variation, the cathodic substrate surface comprises copper, a commonly used material for electronic components such as, for example, leads. Preferably, the germanium and tin are co-deposited onto the substrate surface to a thickness from about 1 to about 10 microns, with an amount of from about 0.5 to about 5 weight percent by weight germanium and 99.5 to about 95% be weight tin co-deposited on the substrate surface.

According to further variations, the germanium-containing compound is selected from the group including germanium dioxide, or other germanium-containing compound that can be solubilized into aqueous solutions, preferably alkaline solutions. Preferably, germanium dioxide is dissolved in a sodium hydroxide solution. According to a still further variation, the germanium-containing compound is provided to the solution directly as a salt, such as germanium fluoroborate, or other water-soluble germanium salt, and combinations thereof. It is understood that the tin-containing compound is added to the solution as a water-soluble salt, preferably tin (II) sulfate.

The present disclosure further relates to a method for mitigating tin whisker growth on a substrate surface comprising the steps of, dissolving an amount of a germanium-containing compound in a basic solution, (preferably germanium dioxide dissolved in a sodium hydroxide solution), adding an amount of water, preferably deionized water, to the germanium-containing compound in solution, adding a complexing agent (preferably d,l-tartaric acid), optionally adding a surfactant/leveling agent, and dissolving an amount of tin-containing compound (preferably tin (II) sulfate) into the germanium-containing solution. A tin-containing anodic electrode is immersed into the germanium-containing and tin-containing solution and a cathodic substrate surface is immersed into the germanium-containing and tin-containing solution. An electrical power source is provided to the anodic electrode and the cathodic substrate (acting as an electrode) comprising a cathodic substrate surface, and then activated to provide an electrical current to the electrodes, resulting in co-depositing an amount of germanium and tin onto the substrate surface. The systems, methods and apparatuses of the present disclosure could also be used and incorporated into systems and methods using a three electrode system with the third electrode being used as a reference electrode.

In a further variation, the present disclosure relates to a method for making an electroplating bath comprising the steps of dissolving an amount of a germanium-containing compound in a basic solution (preferably germanium dioxide in an amount of sodium hydroxide solution), adding an amount of water (preferably deionized water) to the germanium-containing solution, adding an amount complexing agent (preferably d,l-tartaric acid) to the germanium-containing solution, optionally adding a surfactant/leveling agent, and dissolving an amount of water-soluble tin-containing compound (preferably tin (II) sulfate) into the germanium-containing solution. In addition, the present disclosure contemplates an electroplating bath made according to the above method.

In a still further variation, the present disclosure relates to an electroplating bath comprising an amount of a germanium-containing compound in an aqueous solution (preferably germanium dioxide in an amount of sodium hydroxide solution), an amount of water added to the solution, an amount of complexing agent (preferably d,l-tartaric acid), an amount of optional surfactant/leveling agent, and an amount of tin-containing compound (preferably tin (II) sulfate).

Still further, the present disclosure relates to a coating for mitigating tin whisker growth by co-depositing an amount of a germanium and tin onto a substrate surface. According to a preferred variation, the germanium and tin are electro-deposited onto a substrate surface, preferably to a thickness of from about 1 micron to about 10 microns. Preferably, the substrate surface comprises copper, and the germanium is preferably co-deposited with the tin onto the substrate at a concentration of from about 0.5 to about 5 weight percent germanium, and more preferably, from about 1 to about 2 weight percent germanium.

The present disclosure contemplates the described coatings as usefully coating any object, including, but in no way limited to, electronic components where it is desirable to mitigate the formation of tin whiskers by replacing a pure tin-containing surface with a tin and germanium plating.

