November 2012 Archives

Physical properties of functional plating are as follows.

(1) Solderability

This is regarding how well solder bonds with two metal surfaces, and it describes solder affinity and the wetness of solder. This characteristic is indispensable to electronic, semiconductor, electrical and machine parts that require soldering.

(2) Bondability

Connecting the electrodes of semiconductor devices to lead frames is called Bonding. Gold and aluminum wires are typically used for these connections, and how well the connections are made is called Bondability. The characteristics required for the plating are layer softness, surface cleanliness, heat adhesiveness. Gold, silver, electroless nickel platings are used.

(3) Porosity

This is a characteristic of having many minute pores on surfaces where lubricants can be retained. Lubricity is extremely important for the pistons and cylinders of internal combustion engines, and porous industrial chrome satisfies that purpose.

(4) Non-adhesiveness

This means as same as mold releasing ability where objects do not adhere to things. This at the same time relates to low friction coefficient and sliding characteristics. Conventionally, mold releasing compounds were used on rubber and plastic molds in order to promote de-molding of workpieces, but application of dispersion plating with good non-adhesive characteristic enabled molding processes without the mold releasing compounds.

(5) Adhesiveness/Coating adhesiveness

This is a property to improve adhesion quality of metals and organic polymeric materials such as paints, linings, and composite material formations. With automotive radial tires, steel wires are dual layer plated with copper and zinc, then heat treated to be dispersed in order to improve the adhesion with rubber.

Thermal properties of functional platings are as follows.

(1) Heat resistance

This characteristic pertains to the plating nature that resists the plating layer property degradation under high temperatures where the plating layers oxidize and lose hardness.Some plating types can overcome these conditions. As opposed to the industrial chrome and electroless nickel platings losing the hardness when exposed to temperatures of 300°C or more, sulfamate bath nickel plating does not show the hardness reduction at over 500°C, as well as nickel-boron plating also has good heat resistance.

(2) Heat absorbency

This is a characteristic regarding how well the plating absorbs heat, and black coatings are often utilized as similar to light absorbent applications. This is used to absorb heat generated by electrical components to maintain the component temperature below certain levels. Shield casing and etc. are examples.

(3) Thermal radiation

This is a character of radiating heat that has been absorbed, and is important for radiators. It is known that black surfaces have high radiation radiation coefficients, and the black platings are applied to heat sink radiation portion with enlarged radiation surface area configuration.

(4) Thermal conductivity

This is a character about how well the heat is conducted. Silver, copper, and gold are particularly excellent. Copper is often used for practical applications. As a product, thickly applied copper plating on thermal conduction poor stainless steel pan bottom is well known. The copper plating excellent in thermal conductivity maintains the pan bottom temperature even to prevent burning inherent with stainless steel pans.

(5) Thermal reflectivity

This is a property of reflecting infrared of wavelength 2.5 micro meters or more. It is said that surfaces that are mirror-like with white metallic gloss have better thermal reflectivity. Chrome plated reflector plates of electric and kerosene stoves are very well known.

Optical properties of functional plating are as follows.

(1) Anti-reflective characteristics

This is a characteristic that prevents light reflections and glare (Antiglare). For the exterior and light paths of optical devices such as cameras, and automotive interior/exterior parts, black chrome plating, matte nickel-black chrome, black anodizing are used. For zinc plating on steel products, black chromate treatment is used.

(2) Selective Light Absorption

This is a characteristic that shows good absorption of a certain wavelength but does not radiate the lights of other wavelengths. It is often used on the surface of solar collectors. It absorbs the solar heat energy well to produce hot water, but does not radiate the long wavelength infrared from the hot water (therefore the hot water is less likely to cool down). Black chrome plating, black anodizing, black oxide treatment on copper are used.

(3) Light reflectivity

This is a characteristic of how well the light is reflected, and is useful for reflective mirrors. Gloss nickel and chrome plated items are used as automotive rear view mirrors and interior/exterior material for construction. Unlike glass mirrors, the plating has characteristics such as lighter, unlikely to break, and more easily combinable with heat insulation materials. In addition, plated precision finished metal items are used as optical grade components in precision machinary.

(4) Weather Resistance

This is a characteristic that protects plastic, rubber and painted surfaces that are likely to be degraded by the sun's ultraviolet ray. Plastics often deteriorate by the ultraviolet ray and become brittle, cracked and discolored, losing functionalities of products. By plating, such degradation by the ultraviolet ray can be prevented, as well as giving improved aesthetics and sense of luxury.

Electrical properties required for the functional plating are as follows.

(1) Electrical conductivity

The most conductive metal is Silver, followed by Copper, Gold, and Tin. Therefore, these metal platings are utilized on applications requiring good electrical conductivity. In the electronics field, copper plating is indispensable for the through-hole plating to electrically connect both sides of PC boards. Gold, silver, tin, and nickel platings are used on contacts, connectors, and switches. Since gold and silver of high purity produce soft film, alloyed platings of higher hardness are applied.

(2) High frequency characteristics

This is a characteristic in regards to conductivity on millimeter waves and microwaves. On microwave waveguides, it is important that the waveguide surfaces are smooth for low transmission loss performance. For this, copper plating and copper electro-forming are used.

(3) Magnetism

Both dynamic and static magnetic properties are required for magnetic recording media applications. Alloyed platings such as Nickel-Cobalt, Nickel-Cobalt-Phosphorus are utilized.

(4) Low contact resistance

This pertains to how low the electrical contact resistance is. On contacts, switches, and connectors, low electrical and contact resistances are of the importance as well as corrosion resistance, wear resistance, and impact resistance.

(5) Electromagnetic shielding characteristics

Computers and other electronic communication devices are the sources of electromagnetic interferences, as well as they are susceptible to such interferences and may exhibit malfunctions. In order to absorb or shield from these interferences, electroless (copper, nickel) platings are used.

(6) Resistance characteristics

One of the resistive elements used in electronic circuits is ceramic substrate with electroless nickel plating applied. The resistance value can be controlled with the thickness of the plating, and the device has good thermal characteristics and good mass producibility.