Technical possibilities at Metoba
Metoba offers the following techniques for processing Passivation of silver :Reel-to-reel-finishingRack-finishingBulk-finishingKorbtechnik
1. Characteristics and properties
The passivation of silver is a technical application for freshly silver plated surfaces. It is a water-soluble, organic tarnish protection. In the coil coating area, the formation of the protective layer is greatly accelerated by applying a defined voltage. With the high demands placed on electronic components in terms of solderability, tarnish resistance, shelf life, corrosion resistance, durability, pulling and insertion forces, it was essential to look for suitable solutions to meet these requirements. The HF greases used in the past and still used in many areas today are not up to these requirements, as they also bring with them other problems, such as soiling of the greases, which bind the ambient dust to themselves and under certain circumstances can even lead to short circuits. At least as important are the sliding properties of plug and pull contacts. Especially with non-permanent plug connections or automatic switching of the contacts. If the coefficient of friction is too high, deformation of the contacts can occur. Another problem is the cold welding of the contacts. This means that the plugs connect to each other in such a way that it is very difficult or, in the worst case, no longer possible to loosen the contacts. This can lead to damage or complete destruction of the coating system. When silver is passivated, a mono-molecular layer is formed which does not reduce the solderability and conductive properties of electrical contacts. In addition, a long-lasting gliding effect occurs, which reduces the frictional forces and is therefore excellently suited for connector systems.
2. Benefits and areas of application
The passivation of silver is suitable for both technical and decorative tarnishing protection of silver coatings of all thicknesses. It forms a clear layer over the silver coatings without affecting the gloss of the silver. The surfaces are effectively protected against the formation of sulphides. The shelf life increases significantly compared to non-passivated coatings and the protection against tarnishing of the silver remains guaranteed for a long time. The contact resistance and solderability of the silver coating are not affected. In addition, the passivation coatings are non-toxic and non-irritating to the skin, which is why they are also suitable for use in jewellery. It should be noted that passivations on silver can only provide temporary protection.
3. Basic material
Freshly applied silver layers serve as the base material.
4. Required delivery condition
The goods provided must be largely metallically bright. Residual oils or residual impurities must be removable with conventional aqueous alkaline degreasers. Oils containing silicone, alkali/alkaline earth and high-pressure additives must be avoided at all costs.
Passivation of silver coatings is only possible on freshly applied silver layers. With “older” silver coatings, the surface must be activated.