Products Finishing

SEP 2015

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20 SEPTEMBER 2015 — pfonline.com ELECTRONICS E L E C T R O N I C S The second method, based on diffused light measurement, comprises a surface irradiated by a light beam of diameter "d." If the surface is perfectly smooth (perfect mirror), the reflected light is identical to the incident beam. However, if the surface is not perfect, rough diffused light appears together with the reflected light. This diffused light provides the angular distribution of the beam, with values increasing with increase in surface roughness. Silver Layer Samples were prepared using the following process sequence with pretreatment and layer combination variance. The leadframe substrate used throughout was C194 copper alloy. In an initial test series, silver spot plating at 50,100 and 150 A/dm 2 was carried out directly onto the copper alloy substrate. The high-speed silver elec- trolyte contained 70 g/l Ag at pH 8.5. The deposit thickness was 5 µm and the solution temperature was fixed at 65°C and 45°C. Average GAM values of 2.0 were observed for all selected current density/ temperature combinations. A second test series was then carried out with pretreatment and nickel (bright or matt) variation. Reflectivity measurement was carried out on the substrate before and after surface activation with the various pretreatments (leg 1–4), on nickel layers (leg 5–10) and also after silver strike (leg 11–16). Furthermore, a correlation between the GAM value, the diffused light value and the relative surface area increase (RSAI) was also established. RSAI roughness values are normally measured using an interference micro- scope and calculated from a topographic comparison of the sample's three- dimensional surface mapping and its two-dimensional projection. An RSAI value of 100 percent would mean a doubling of the surface area. The graph at the right presents the three different measurement values for all 16 test combinations. It clearly shows the enhanced diffused light readings and the excellent correla- tion between all three techniques. High Optosurf values correlate with an increased surface roughness (RSAI) and hence low light reflectivity (GAM). An RSAI value of 5.39 (leg 3) corre- sponds to a 5.39 percent increase in surface area, whilst the best surface condition (mirror bright) of 0.04 is as expected from a polished surface with a highly levelled nickel interlayer (leg 15). In general, the use of a bright nickel barrier layer provides significantly lower diffused light values and higher GAM readings, whereas a silver strike layer causes a negative effect. Electropolishing further improves values of the base material. The leg 14 conditions were then used for further high-speed silver plating tests (100 A/dm 2 , 60 g Ag/L) at varying brightener concentration (1–10 mL) for a 5µm deposit. In all cases, GAM values of over 2.0 were achieved with best results at a brightener concentration of 2–3 mL/L. A further test series was carried out at 50 A/dm 2 for varying g/L silver in the electrolyte. Results show an expected reduction in GAM value at increasing silver concentration. This optimized silver process containing the new bright- ener system was tested at a selected customer. Initial tests were carried out using an electrolyte containing 60 g/L Ag over Tell Us Your... And We'll Give You... the tank options and price best suited to your needs! Since 1960 Factory and Headquarters: Owosso, MI www.tri-mer.com © 2015 Tri-Mer Corp. Call Greg Worthington today: 989-723-7838 or email at gworthington@tri-mer.com • 1" solid polypropylene tanks for unmatched strength; copolymer, steel and stainless steel tanks. • Tanks are factory tested for 72 hours and certified leak-free. • Ventilation packages available. Process, Temperature & Capacity

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