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MARCH 2025 I PCB007 MAGAZINE 13 gold seedings are plated, they act as a catalytic surface, initiating the formation and activat- ing the reducing agent. is so-formed reduc- ing agent supplies the electrons. is autocat- alytic reaction is potentially infinite and plays a major role in the deposition process of Type III electrolytes. In the literature, there is currently no unified nomenclature to designate these different depo- sition types. Types I and II are oen referred to as immersion gold (IG). Type III may also be referred to as autocatalytic gold (AG). For the mixed reaction gold bath types, anything on the naming spectrum between IG and AG is cur- rently used in the industry. is could be the case since they contain shares of both. Plating Properties of Different Gold Electrolytes Each type of gold electrolyte has unique properties and applications, influencing the final finish's quality and performance. By Figure 1: Schematic: Types of electroless gold electrolytes. Figure 2: SEM images of a through-hole entrance with an ENIG deposit plated with a) immersion type I; b) mixed reaction type (low autocatalytic, II); c) mixed reaction type (high autocatalytic, III) 1 . examining these electrolytes, we can better appreciate their specific advantages and disad- vantages in metal plating. Let's delve into the various gold electrolytes and their characteris- tics to gain a comprehensive understanding of their roles in achieving optimal plating results. First, let's examine their performance in ENIG layers in terms of nickel corrosion, as IPC-4552A shed light on this important topic a couple of years ago. For the first time, this specification has done the job of quantify- ing the level and acceptance of nickel corro- sion, providing concrete data instead of fears. e various reaction mechanisms of the three different types of gold baths are evident in the type and frequency of corrosive attacks obser vable in the ENIG coatings. Figure 2 gives an exemplified impression of their dis- tinct performance. In an immersion bath, spike or spreader- shaped corrosive attacks can be observed, especially at through-hole entrances where a