Abstract
We report on structuring copper representing soldering pads of printed circuit boards by laser-induced periodic surface structures. Femtosecond laser radiation is used to generate low spatial frequency laser-induced surface structures, having a spatial period of 992 nm and a modulation depth of 120 nm, respectively. The slump of screen-printed solder paste is measured to compare the solder coverage on the pads after the solder process on a hot plate. A comparative study of the coverage of solder paste on a fresh polished pad, a pad stored for two weeks, and femtosecond laser-structured pads reveals the improved wettability of structured pads even after storage. In addition, leaded and lead-free solder pads are compared with the particular advantages of the solder-free pad when periodically laser structured. Our findings are attributed to two major effects: namely, the increase of the surface area and the improved surface chemical wettability. Overall, the application of laser-induced periodic surface structures helps to reduce the demand of lead-based solder in the electronic industry and provides a feasible method for a fast and spatial selective way of surface functionalization.
Highlights
Electrical connection pads, e.g., metallic solder pads, represent a key part in the packaging of printed circuit boards in electronics [1]
We report on structuring copper representing soldering pads of printed circuit boards by laser-induced periodic surface structures
The structures can be identified as low spatial frequency laser-induced periodic surface structures (LIPSS) (LSFL) [26]
Summary
Electrical connection pads, e.g., metallic solder pads, represent a key part in the packaging of printed circuit boards in electronics [1]. After transport or storage, electrical connection pads can be covered by a layer of metal oxide, in turn leading to a gradual digression of the solderability of the electrical connection pads [3]. They might be no longer usable and must be disposed with both negative economic and environmental impacts To overcome this deficiency, protective layers are considered. Layers of noble metals such as silver or gold are used, covering the electrical connection pads during transportation or storage in order to avoid exposure to ambient atmosphere and to prohibit the formation of oxide layers [4]. The additional material required for the protective layer increases the production costs and requires dedicated steps and equipment in the manufacturing process of printed circuit boards
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