PCB007 Magazine

PCB007-Mar2021

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44 PCB007 MAGAZINE I MARCH 2021 RAIG was introduced a few years ago to meet the requirements of newer designs. Since its inception, more designers are finding RAIG gold to be a viable alternative to standard im- mersion gold. RAIG gold is a mixed-reaction bath that functions as immersion gold; with a reducing agent, it also functions as an electro- less (autocatalytic) bath. e reactions start simultaneously with the introduction of the substrate (nickel, palladium, or copper). Because the immersion reaction is a displacement reaction, it diminishes over time as the substrate becomes less available for depo- sition. e electroless reaction continues, rely- ing on the reducing agent present in the electro- lyte, rather than on substrate availability. RAIG gold is limited in how much gold it can deposit, as compared to a pure electroless gold. It is ide- ally suited for deposits of 3–6 minutes. Curbing the immersion reaction and allow- ing gold thickness to build autocatalytical- ly expands the operating window by allow- ing thicker gold to deposit without nickel cor- rosion. A thicker gold layer (3–6 mins), is be- yond the capability of standard immersion gold electrolytes, but is desirable for many ap- plications, as it widens the operating window for gold wire bonding. Figure 1 shows the relationship between gold thickness and the strength of the wire bond. RAIG (Reduction-Assisted Immersion Gold) for Gold Surface Finishes The Plating Forum by George Milad, UYEMURA Figure 1: The effect of gold thickness on the operating window of the bonding force.

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