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70 PCB007 MAGAZINE I JUNE 2023 RAIG was introduced a few years ago to meet the requirements of newer designs. Since its inception, more gold finishes are finding RAIG to be a viable alternative to standard im- mersion gold. RAIG is a mixed reaction bath that functions as an immersion gold and, with the added reducing agent, it also functions as an electroless (autocatalytic) bath. e immersion reaction initiates the gold plating with the introduction of the substrate (nickel, palladium, or copper) into the electro- lyte. e deposited immersion gold layer will trigger the electroless reaction. Being a dis- placement reaction, the immersion reaction will diminish with time as the substrate be- comes less available with deposition. e elec- troless reaction will continue, as it relies on the reducing agent present in the electrolyte and not on substrate availability. RAIG is limited on how much gold it can deposit, as compared to a pure electroless gold. It is ideally suited for thicknesses of 3–8 µins. Limiting the immersion reaction and allow- ing gold thickness to build up autocatalytically opens the operating window by allowing thick- er gold to deposit without nickel corrosion. A thicker gold layer (3–8 µins), which is beyond the capability of standard immersion gold elec- trolytes, is desirable as it widens the operating window for gold wire bonding. Figure 1 shows the relationship between gold thickness and the strength of the wire Reduction Assisted Immersion Gold for ENEPIG Surface Finish The Plating Forum by George Milad, UYEMURA Figure 1: The effect of gold thickness on the operating window of the bonding force.