PCB Fabrication

An Overview Of Immersion Gold Enig Surface

by:A-TECH      2020-11-11

In right now’s advanced circuits, this surface end is very limited as a result of it requires that each one surfaces to be plated should be electrically related (i.e. an electrical charge have to be present for plating). These interconnections must then be broken to make the circuit practical. The plated nickel could be very solderable and never subject to the solderability problems with ENIG. The plated gold has no limits on thickness and may help wire-bonding processes like Thermo Compression Bonding (i.e. ball bonding). With the pending lead-free legislation impacting PCB manufacturing on a world scale, the immersion silver process is rapidly gaining recognition because the lead-free floor end of alternative.

Solderability testing has been very favorable and the corrosion protection of the film in combined flowing fuel has been exceptional. The thinness of the film permits low resistance contact throughout in-circuit testing. This surface finish has the potential to be a good substitute for ENIG/ENEPIG with the potential cost being significantly less. The nature of this film permits it to replace the solder mask altogether for some purposes. Note that this coating is also very promising as a conformal coating that could possibly be utilized after meeting of parts.

Electroless nickel immersion gold consists of a skinny layer of gold over a thick layer of nickel. Plating gold instantly onto copper is not efficient since copper will rapidly diffuse by way of the gold and oxidize on the floor . Nickel serves as a barrier layer to copper, though Ni can eventually also diffuse to the surface of gold and trigger the identical solderability problem . Typical ENIG specifications are defined by IPC4552 Specification for Electroless Nickel/Immersion Gold.

The nickel thickness must be in the vary of three-6 µm which is adequate to forestall porosity by way of to the bottom copper. The nickel is plated with an autocatalytic process with phosphorus lowering brokers. This phosphorus will get included into the deposit within the range of eight-12%.

The gold thickness is specified as 0.05 µm minimal (2 µinches) at 4 sigma normal deviation beneath the imply. One of the extra popular floor finishes within the PCB business, ENIG overcomes several shortcomings of other surface finishes. The software process for ENIG consists of two components—the primary part requires the applying of a layer of Nickel to function both a barrier on the copper floor and act as a floor glorious for soldering. The second part includes making use of a layer of Gold to act as a safety for the layer of Nickel, so long as the board is in storage before meeting.

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