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22 SEPTEMBER 2015 — pfonline.com ELECTRONICS E L E C T R O N I C S a current density range of 70 to 100 A/dm 2 for a standard brightener system and using alloy C194 as substrate. Deposits showed poor brightness uniformity and GAM readings could not be measured. A repeat series of tests was then carried out using the new silver brightener system, achieving consistent GAM values of 2.0 and above. In addition, silver was deposited onto both bright and matt nickel interlayers, providing greater than 2.0 GAM readings in each case. Separate measurements were carried out on both selec- tive silver (spot) and the nickel interlayer (background), providing a 0.4 GAM value for matt nickel compared with 2.34 for bright nickel. The high GAM results (regardless of the nickel inter- layer) highlights the advantage of the new silver bright- ener system in providing the high levelling characteristic needed to achieve the required reflectivity without using nickel levelling additives. Hence the technical functionality (bondability) of the silver may be maintained even after heat treatment, compared with the expected negative effect (due to the higher organic content) when a bright nickel barrier layer is used. Effect of Heat Treatment The same customer site was used to evaluate the effect of heat treatment for the new brightener system. Silver deposits were heated for one hour at 200°C and for two hours at 170°C. As expected, subsequent GAM measurements showed significant reflectivity losses. A new post-dip was developed to prevent reflectivity loss due to heat treatment of silver coatings. Tests were carried out to highlight the benefit of this aqueous post-treatment, which uses organic additives to effectively prevent discolor- ation due to heat exposure. All test samples were heated to 200°C for an extended duration of two hours, with GAM measurements at varying post-dip immersion times. A similar loss in GAM reading could only be observed for the shortest immersion time of three seconds. Consistent GAM readings were maintained for higher immersion periods with no observed discoloration of the silver deposit. To confirm the effectiveness of the post-dip, irrespective of nickel type, a final test series was carried out for both bright and matt nickel interlayer. Immersion times ranged from 10 to 60 seconds and the test samples were heated to 310°C for 15 minutes after the final post-dip treatment. Within experimental accuracy, these GAM results clearly confirm the effectiveness of the post dip treatment, irrespec- tive of the interlayer nickel type used. Summary Functional silver coatings that provide ultimate reflectivity are required for future generations of high-power, energy- saving LEDs. This reflectivity property is normally measured using a light transmission densitometer and expressed as a GAM reading. For the type of LED described in this paper, GAM values of greater than or equal to 2.0 are required. To meet these requirements, a new low free-cyanide silver brightener system has been developed, providing mirror- bright deposits over a wide current density range (to 150 A/dm 2 ). Investigative work included the effect of substrate pretreatment. Acid activation, micro-etching and electropo- lishing were all assessed, with the latter providing expected benefits, confirmed by GAM and diffused light readings. Optical properties were further enhanced when the inter- layer nickel type was replaced with a high levelling bright- ener system. As expected, the brightener-free silver strike step provided a loss of brightness. These studies also highlighted the exceptional levelling properties of the new silver brightener system in achieving the target of greater than or equal to 2 GAM value, irre- spective of which nickel interlayer type was used. A new post dip treatment was also developed and its effectiveness demonstrated, providing minimum silver discoloration after heat treatment for both 200°C at two hours and 310°C at 15-minute conditions. Olaf Kurtz, Jürgen Barthelmes, Robert Rüther are with Atotech Deutschland GmbH; Joko Setyadi-Lie is with Atotech S.E.A. Pte Ltd. Contact them at olaf.kurtz@ atotech.com. Bright Lights, Big Finish for Electronics Plater Wisconsin manufacturer of printed circuit boards for the LED lighting industry and others in the electronics sec- tor has seen business boom in the past few years. short.pfonline.com/Bergquist GAM measurements before and after heat treatment. NICKEL BASE TREATMENT BEFORE AFTER Nickel Sulphamate 10 sec 1,985 1,885 20 sec 1,920 1,885 30 sec 1,960 1,950 40 sec 1,890 1,745 50 sec 1,845 1,615 60 sec 1,880 1,755 Makrolux 10 sec 2,040 1,930 20 sec 2,005 2,020 30 sec 2,005 2,010 40 sec 2,020 1,855 50 sec 2,010 1,945 60 sec 2,015 1,960