AuNic: Dummy Plating Free ENIG Process

In the early nineties of last century composite coatings of electroless nickel-phosphorous and immersion gold (ENIG) started to raise attention of assemblers of electronic components on PCBs. Referred to as ENIG, this final finish is appreciated due to its planarity, its ability to multiple soldering, easier post solder inspection, bondability (Al-wire bonding) and the presence of a precious metal contact surface among other favorable features. The properties of an ENIG finish are unique and provide a high funtional versatility.

Nowadays the benefits of ENIG are well established and its application is still increasing even after significant growths in the past years and being under scrutiny most of the times for cost reasons. The AuNic-process provides a uniform nickel/gold-layer plated by a medium phosphorous electroless nickel bath and an immersion gold bath. It is characterized by excellent surface wettability during soldering.
Commonly it is necessary with ENIG plating to perform dummy plating with a certain loading factor with the electroless nickel bath. This takes place after a new make-up and before resumption of production after idle time. The purpose is to generate sufficient plating activity and avoid plating defects. It also causes production down time and hence reduces capacity. It inflicts additional cost as extra chemistry is consumed.

Atotech developed an electroless nickel bath, AuNic EN, which can omit the dummy plating. Due to formulation, sufficient activity is achieved after a new make-up and an additive re-activates the bath after idle time
 
AuNic - The Process
AuNic is a drop-in process for existing standard ENIG lines. It consists of five main steps: cleaning, micro-etch, activation, electroless nickel and immersion Gold.

Features and Benefits:

• Dummy-free electroless nickel
  -> lower chemicals consumption
  -> higher equipment utilization
• 6 MTO for electroless nickel
  -> higher equipment utilization
• Low gold concentration Immersion Gold bath (1 g/l)
  -> lower precious metal costs
• Based on Atotechs extensive ENIG production experience
  -> best suited for on/off production mode

The Additive Controlled System

The AuNic additive increases bath activity after idle times, allowing for immediate production start without dummy plating.