Patent Application
20060169744
1. Field of the Invention
The present invention is directed to replaceable soldering tips of the type in hand-held soldering devices, particularly those which are used in producing solder used for mounting electrical components on electrical circuit boards.
2. Description of Related Art
Up to now, generally speaking, all soldering tips have been made basically made the same way. A piece of copper is machined to the desired geometry, then it is plated with iron. Iron is plated on the tip to protect the copper from the corrosive action of the solder and flux, as well as to compensate for the relative softness of the copper with a hard coating. While solder and flux will also dissolve iron over time, it takes significantly longer for solder and flux to dissolve iron than copper. Even through iron has poor thermal transfer qualities, it is selected as a protective coating over the copper because of its durability and ability to wet with solder. Once the tip has been plated with iron, the working end is masked and the rest of the tip is plated with chrome or nickel/chrome, which will not wet with solder for the purpose of keeping the solder on the working end of the tip.
Until recently, most solders that have been used have been lead/tin eutectic solders. However, the use of lead-free solders is becoming a legislative requirement around the world. Lead-free solders contain in excess of 94% tin which is much more corrosive than traditional lead/tin eutectic solders. Lead-free solders also require higher temperatures to melt, further exacerbating the corrosive environment. Additionally, because of the poor wetting properties of lead free solders, chemically aggressive fluxes are used with such solders. The combination of the high tin content, higher operating temperatures, and chemically aggressive fluxes dramatically reduces the working life of a soldering tip and results in higher operating costs for soldering operations.
Increasing the iron thickness of the coating on the tips is often thought to be a good solution to the problem, but the amount of additional iron that has to be added to ensure the same working life reduces the ability of the tip to transfer heat so much that it is virtually impossible to solder with these tips. As a result, at best, a compromise must be made between useful life and heat transfer rate, resulting in a tip that does not transfer heat adequately and does not last as long.
Other types of bonding tools, such as those used for thermocompression bonding, an operation which is performed in a different manner and at higher temperatures than soldering with a soldering iron (around 800° C. to 1200° C. vs. around 170° C. to 190° C. for lead solders and around 217° C. to 227° C. for lead-free solders) using, for example, a brazing solder, have a need to use coatings on the bonding tool that are more resistant to wear and corrosion due to the higher loads and temperatures to which such tools are subjected. See, e.g., the bonding tools of Sumitomo Electric Industries, Inc which apply a polycrystalline diamond coating to the bonding tool via gaseous phase synthesis and vapor deposition techniques as are described in U.S. Pat. Nos. 5,516,027; 5,653,376 and 5,934,542.
Accordingly, it is a primary object of the present invention to provide a soldering tip with wear- and corrosion resistant coating which will be suitable for soldering tips of the type used on hand-held and machine or robot held soldering irons, and which will have an extended life even in the environment of lead-free soldering with corrosive fluxes.
This object is achieved in accordance with the present invention by hardening the outer surface of the tip's iron plating so that it is able to withstand the chemically and thermally corrosive environment when using lead free solders through the addition of hardening agents to the electroplating solutions used to coated the copper base material of the tip. The hardening agent used in accordance with the invention is micron size particles of materials that are harder than iron and are chemically inert, such as, but not limited to natural and synthetic types of diamond, ruby, sapphire, silicon, alumina, etc. The additive becomes part of the iron plating matrix as it deposits onto the copper of the soldering tip. A uniform dispersion of the additive is desired, and the final surface may be smooth or rough. However, a slightly textured surface, e.g., a surface quality Ra of from 50 μm to 0.10 μm, is beneficial when using lead free solders as it provides more surface area and eases the difficulty in wetting the lead-free solder to the tip.
In accordance with a preferred technique, a solution of at least one metal salt in which micron size diamond particles are distributed is used to electroplate a protective layer onto the copper base of the soldering tip of at most about 1.5 mm. In particular, in a preferred version, the plated-on tip coating is formed of an iron matrix in which the diamond particles are substantially uniformly distributed.
The soldering iron 1 of
The soldering tip 5 has a soldering portion 5b that is shaped for forming of a solder joint. In
However, instead of being formed of a copper core to which an iron coating has been applied, at least the soldering portion 5b of the soldering tip 5 has a copper inner base material to which a wear and corrosion resistant coating has been applied that is comprised of a matrix of a metal that is harder than the copper inner base material, and in which micron size particles of a chemically inert material that is harder than iron are dispersed. The chemically inert material can be any one of diamonds, rubies, sapphires, silicon, and alumina, diamonds being particularly preferred. While the matrix material is preferably iron, it can be nickel, nickel alloys, nickel/phosphorous alloys. silver, silver alloys, gold, or gold alloys.
The preferred manner of forming the coating is by electroplating, e.g., in the manner describing in U.S. Pat. No. 3,762,882, which patent is hereby incorporated by reference. However, other techniques can be used, such as gaseous phase synthesis and vapor deposition techniques.
The matrix and particle coating MP (
It has been found that soldering tips in accordance with the present invention have a heat-up time that compares favorably with standard iron plated copper tips, yet wear much longer, especially when lead-free solder are used with and without fluxes. In fact, the increased life and performance of composite tips produced in accordance with the present invention is able to offset the higher cost of production of the composite coated tips of the present invention relative to conventional plated iron tips.
It should be appreciated that the present invention is not intended to be limited to the specific characteristics shown and described herein, but rather the invention is intended to encompass other methods, materials and constructions that those skilled in the art will recognize as be at least equivalent to those described herein.
