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46 I-CONNECT007 MAGAZINE I JULY 2026 solution as designers are faced with 1.6T/3.2T 6G. We are seeing frequencies above 77 GHZ and beyond. So, what is the answer? Immersion Silver-Immersion Gold (ISIG) Immersion silver has been used commercially as a solderable finish for more than 25 years. Its high conductivity makes it especially well-suited for high-frequency applications, where signal integrity becomes increasingly important. Alkaline Immersion Silver Most immersion silver processes are acid-based. The process described here uses an alkaline formu- lation as an alternative approach. This chemistry was developed to support high-frequency perfor- mance while addressing some of the limitations associated with conventional acid-based systems. Development of ISIG To further enhance the performance of alkaline immersion silver, a specialized immersion gold process was developed for deposition over the silver layer. This combined finish, immersion silver- immersion gold (ISIG), was designed to improve signal integrity and reduce attenuation loss in 5G applications. The initial development effort focused on immer- sion silver alone, since silver is already recog- nized for its ability to improve high-frequency performance because of its superior conductivity. However, concerns about silver tarnishing through environmental interaction led to the addition of a thin immersion gold overcoat, creating a more robust dual-finish system. The alkaline formulation of immersion silver has mitigated one of the most annoying issues associ- ated with acidic immersion silver processes: solder mask interfacial attack. This is often known as trench etch (Figure 1). The interfacial attack is often blamed for the genesis of creep corrosion, which is often related to exposure of the circuits to harsh environments. Nitrate-based formulations are overly aggres- sive on copper. This leads to voiding along the T RO U B L E I N YO U R TA N K Figure 1: Solder mask interfacial attack (SMIA).