Beryllium copper fingerstock gaskets are the product of choice for creating an EMI seal in electronic enclosures. For the gaskets to function properly, Leader Tech recommends that they be placed in contact with metallic, conductive surfaces. Because every application is different, designers must take into consideration what type of metal their enclosure is made from and select the correct finish for their gaskets.
Plating can affect conductivity, wear characteristics, and the possibility of corrosion in a gasket. It is important to select the correct finish to reduce the potential difference between dissimilar metals. The chart to the right shows galvanic compatibility between various metal types and different selections of plating. For example, see that the bar for the Nickel compatible surface finishes intersects with brasses in group number 9, however, it does not intersect with cast aluminum shown in group number 20. The red, green, and blue color sections of the bar graphs describe different types of environments. If a metal and a finish cross within the blue bar, they are acceptable in a controlled, indoor, office type of environment, with a maximum voltage difference of 0.5V. The red bars represent a corrosive environment, such as a marine application. If metal and a finish do not cross within the red bar, then they are not an acceptable match for a harsh environment, which requires a maximum voltage difference of 0.1V. For galvanic corrosion to occur, a catalyst is needed between the two surfaces. Water, as in humidity in the air of an outdoor environment acts as that catalyst. The salt in seawater further facilitates this reaction by increasing the water’s conductivity.
Leader Tech offers a full line of plating solutions for any application. The chart to the left shows our standard options, the corresponding specification, and the finish code that is inserted at the end of a beryllium copper fingerstock stock code. These plating options can also be modified to fit a specific application. The majority of Leader Tech’s plating options are RoHS compliant but non-RoHS finishes are also available such as tin-lead, cadmium, and zinc/yellow chromate.
While many different plating options are available, a select few cover the vast majority of applications.
BD: Bright Finish
This finish option is actually just unplated beryllium copper. To achieve the material’s spring properties, beryllium copper is subjected to a heat treat process. This also creates an outer oxide layer that gives the material a bright appearance and provides some resistance to corrosion. The bright finish option is often acceptable if the gaskets will be used in a controlled environment and has the added benefits of no additional costs or lead time.
SN: Bright Tin
Bright tin plating is perhaps Leader Tech’s most popular finish option. Our standard specification is per ASTM B545, Class A, which has a minimum thickness of 100 microinches. Tin plating is typically used when mating a gasket to aluminum or 300 and 400 series stainless steels. It increases solderability due to tin’s low melting point of 232°C (450°F) and provides some light wear resistance while remaining one of the lowest cost finish options.
Electro-less Nickel
Nickel plating is Leader Tech’s best recommendation for applications that require high levels of wear and corrosion resistance, as well as high-temperature applications with a melting point of 890°C (1630°F). For example, an electrical contact that will endure a high number of cycles, as well as high heat, should be plated with nickel. Leader Tech’s standard Nickel plating is per ASTM B-733 and is an electroless process. This type of plating does not use an electric current to adhere to the metal and provides a more uniform finish thickness. With electroplated nickel, the plating has a tendency to build up at the electrode points, creating a higher variance in plating thickness across the part.
Leader Tech’s engineering team can assist with the selection of the correct type of plating for your application. Just provide the specific environment, contacting metal, and intended usage. Contact your representative for details.
