Wetting of New SnAg Surface Finish Alena Pietrikova 1) , Daniel Dzivý 1) , Olga Vrublenskaya 2) , and Marina A. Shikun 3) 1) Faculty of Electrical Engineering and Informatics Technical University of Kosice, Kosice, Slovakia 2) Research Institute for Physical Chemical Problems of the Belarusian State University, Minsk, Belarus 3) Belarusian State University, Minsk, Belarus alena.pietrikova@tuke.sk Abstract: This paper shows how a surface finish does affect wettability. Four standard lead-free alloys selected for surface finishes on PCB (LF HASL, ImSn, ENIG, and Cu) with a newly developed surface finish based on SnAg7 alloy were compared. Wetting characteristics of surface finishes were analysed using the spreading rate method and a method based on wetting reflow pattern, both in laboratory condition. Experiments were supplemented by analysis of the effect of plasma on the flux activity, and eventually on wettability. A self-developed equipment was applied to evaluate the spreading rate. The spreading rate method allows for real-time measurement of contact angle of liquid SAC 305 solder balls on various PCB surface finishes. The method based on wetting reflow pattern by SAC 305 solder paste applied on various PCB surfaces confirms these wetting characteristics. The wettability of the new and relatively cheap SnAg7 surface finish is almost comparable with surface finish based on ENIG. This new surface finish is a prospective material that offers interesting properties for application in electronics. 1. INTRODUCTION The wettability of a surface by a liquid depends primarily on the contact angle between the surface and molten solder ball in a liquid state. The contact (wetting) angle as well as the spreading rate of molten solder are important parameters in determining the wettability of the molten solder on a solid substrate. Motivation for the study how does surface finish affect wettability are various industry aspects. However, in the case of soldering in electronics it is necessary to take into account that it is a reactive wetting, in which a reaction takes place between the spreading solder and the solid substrate. Wettability is influenced by surface energy and this is related to the option of PCB surface finish [1, 2, 8, 9]. The production price, reliability and variability of application of other technological processes are also important. This paper focuses on the wettability characteristics of a new surface finish and our first analyses point to promising results of the use of this SnAg based finish [3]. In addition to temperature, wetting also depends on the type of surface treatment and the overall state of the surface energy. ENIG (electroless nickel/ immersion gold) based PCB finish began to be used in electronics as an alternative at the end of the last century, at a time when electronics was looking for a substitute for lead, which was part of the Hot-Air Solder Leveling-based (HASL) coating [4]. This surface treatment is charac- terized by long-term reliability while maintaining a well-wettable surface, so manufacturers have started to use it more and more. However, the problem is the high price and also the corrosion of nickel, which is associated with black pads. From the point of view of reliability, the organic solderability preservative (OSP), Immersion tin (ImSn), immersion Ag and also lead-free HASL (LF HASL) are also used as an alternative to lead. Each of these surface finishes has its advantages and disadvantages. In our article, we present a new type of surface finish based on SnAg. This type of PCB surface finish has not yet been applied in the field of SMD technology. The wettability of various PCB surface finishes was evaluated by a self-developed method that allows for the real-time measurement of the contact angle under laboratory conditions. The wettability of standard surface finishes was compared with the newly- developed surface finish based on SnAg. Within this experiments we investigated an effect of combination flux - plasma on wettability as well. 978-1-6654-6589-2/22/$31.00 ©2022 IEEE 1 45th Int. Spring Seminar on Electronics Technology (ISSE) 2022 45th International Spring Seminar on Electronics Technology (ISSE) | 978-1-6654-6589-2/22/$31.00 ©2022 IEEE | DOI: 10.1109/ISSE54558.2022.9812833 Authorized licensed use limited to: Technical University Kosice. Downloaded on November 28,2022 at 11:58:51 UTC from IEEE Xplore. Restrictions apply.