Study on Weak Alkaline Cyanide-Free Silver Plating Process for Etching Lead Frame

Abstract

As a new development direction of integrated circuit chip carrier, etched lead frame has been gradually applied in microelectronics industry in recent years. Since the preparation of the etched lead frame requires the use of multiple layers of non-alkali-resistant photoresist films with specific patterns, and the traditional cyanide silver plating is unable to meet this requirement, making that the development of weakly alkaline cyanide free silver plating process has great significance. In this paper, a weak alkaline silver plating process based on 5,5-dimethylhydantoin (DMH) cyanide-free silver plating system was studied. The electrodeposition behavior of the system and the nucleation mechanism of silver crystallization were investigated by cyclic voltammetry (CV) and chronoamperometry (CA); By changing a series of conditions, the effective working range of the process was determined, and the properties of the coating and the bath were characterized under the optimized process conditions. The results showed that the crystals of the silver plating layer were fine, and the average particle size was 16.7 ± 3.6 nm. From the XRD test results, the effective grain size was 43.6 ± 3 nm, and the (200) crystal surface was the preferred orientation crystal plane. Coating performance tests included whiteness, brightness and hardness, which were 7.2%, 117 Gs and 74 ± 4 Hv, respectively. In addition, the performance test of the bath showed that the current efficiency of the bath reached 99.2% with the temperature was 30 ^oC and the current density was 0.6 ASD, and the throwing power was about 83% at 30 ^oC. The results of the above tests and the actual etched lead frame samples have demonstrated that this process is of great value in practical application.

Keywords

cyanide-free silver plating / lead frame / nucleation mechanism / bath properties / coating properties

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