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PRODUCTS FINISHING — pfonline.com 19 PLATING LED LIGHTS Insoluble anodes are used in these high-speed silver processes with the inevitable release of small amounts of free cyanide during electrodeposition . The silver coating must possess excel- lent reflectivity to meet the requirements needed for the manu- facture of the high-power LEDs used in TV screens. Reflectivity can normally be measured using either a trans- mission densitometer, providing a GAM value, or by measuring the angular distribution of diffused light of a defined wave- length emitted from an irradiated sample. The densitometer quantitatively determines the color density, or the amount of color per unit of area. During measurement, a defined wavelength light source is irradiated onto the respective coating and the reflected light photo-electrically measured (remission value). The measured density values (often called GAM readings) typically lie between 0.0001 and 2.0. The name is derived from the original densitometer manufacturer, G.A.M Co., and is now widely accepted as the industry standard. The larger the GAM value, the higher the reflectivity of the surface. For LED applications, different GAM values are required for the respective LED performance with 1.2–1.4 for the lower range and 1.8–2.0 for the upper range. Future LED generations require GAM values greater than 2.0, and in order to meet these requirements, novel silver plating brightener systems have been developed for both rack and reel-to-reel applications. The new Silvertech LS LED and Silvertech HS LED processes contain zero or minimal levels of free cyanide, thereby enabling the use of inert anodes. Typical deposit hardness values of 120–140 Hv can be achieved, and for reel-to-reel spot plating applications, current densities as high as 150 A/dm 2 may be used. A degree of variance also occurs with the deposited layer structure prior to the final bright, highly-reflective silver coating. For example, the LED substrate (circuit boards, ceramics) are initially copper plated, followed by a nickel barrier layer prior to silver plating. For the plating of lead- frames, it is also possible to directly apply the silver onto a highly levelled copper electrodeposit as an alternative to the nickel barrier layer. Alternatively, overall brightness improve- ment can be accomplished by pretreatment modifications such as the introduction of electropolishing or micro-etching steps. Extensive studies have been carried out investigating the effect of process sequence, including pretreatment and type of nickel process used (matt or bright) on the final coating brightness and reflectivity properties. Surface reflectivity was determined using both a densi- tometer and a diffused light measurement. The inner workings of a typical LED light. Photo courtesy of Smartcharge. LEDs & MCPCB Bulb shell Ring PCBA (Driver) Housing Samples were prepared using this process sequence with pretreatment and layer combination variance. Components Step 1 Uniclean 211 / Puronon RTR (Soak cleaning) Step 2 Uniclean 260 / Puronon RTR (Electrolytic Degreaser) Step 3 Descabase CU / ElectroGlow / Uniclean 675 (Copper Etching/ Polishing/ Acid Dip) Step 4 Nickel Sulphamate HS / Macrolux (Nickel Plating) Step 5 Silver Strike Step 6 Silvertech LS LED / Silvertech HS LED (Silver Plating) Step 7 Argalin LED (Post-treatment) Battery (2200mAh, 7.4v) PCBA (Intelligent Control)