ENEPIG is Electroless Nickel Electroless Palladium Immersion Gold, it’s a PCB board surface finishing. Some engineers also call it ENIPIG, Do you know the difference between them?
ENEPIG and ENIPIG are immersed in a layer of palladium between the nickel layer and the gold layer, which can prevent the mutual migration between nickel and gold, and no black pad will appear.
They all have strong wire bonding ability, good solder joint reliability, ability to withstand multiple reflow soldering and excellent storage time, etc., and can correspond to and meet a variety of different assembly requirements.
The ENEPIG plating thickness is different. If thin palladium (replacement palladium) with thickness 0.0125-0.02um (0.5-0.8u”), we call it ENIPIG. If thick palladium with thickness 0.05-0.5um (2-20u”), we call it ENEPIG.
Like other surfaces, Oil removal is the first important process of surface treatment. Remove mild oil and oxides on the copper surface, clean the copper surface and increase wettability.
Feature requirements:
Microetching is surface roughening. It can remove the oxide layer on the surface of copper foil, and etch away 1um~2um copper from the surface of copper substrate. Increase the adhesion between copper and chemical nickel layer.
The method of using an acid solution to remove scale and rust on the copper surface is called acid cleaning.
The role of pre-dipping is to maintain the acidity of the activation tank and to make the copper surface enter the activation tank in a fresh state (no oxides).
The activation solution is ionic palladium. It solves the copper surface cannot be directly electroless nickel plated. In addition to require a layer of firmly bond palladium on the copper surface.
In order to ensure the solder reliability, the electroless nickel layer is required to have high ductility. The phosphorus content in the nickel layer is related to the weldability and corrosion resistance of the coating, and the phosphorus content is generally required to be 7-9%. Too low phosphorus content easy to reduce solderability and strength of soldering.
Adding chemical Palladium process between the chemical nickel and chemical gold to prevent the generation of black pads.
At present, the main components of chemical palladium used by our company are PdCl2, NaH2PO2, complexing agent ammonium hydroxide, accelerator and stabilizer ammonium chloride, etc.
The chemical gold process is directly deposited on the base of chemical palladium on the body, the mechanism is a displacement reaction.
It is the use of large difference of electrode potential between nickel-palladium and gold electrode. Nickel and Palladium can replace the gold ions in the plating solution.
When nickel or palladium surface are placed by gold. The replacement can still continue until the nickel layer or palladium layer is full covered by the new gold layer as the gold layer is porous.
Flash Gold acts as a metal resist, which is resistant to all common etching solutions. It has a high electrical conductivity and is an ideal metal for corrosion resistance and an ideal contact surface metal with low contact resistance.
Flas gold has strong conductivity, good oxidation resistance, long lifetime.It often used in gold bonding, repeatedly unplugging and contacts pads PCB boards as its high dense coating and relatively wear-resistance.
Flash gold is very high cost, poor welding strength.
The immersion gold process uses chemical oxidation-reduction reaction to form a layer of gold coating. It deposits a nickel-gold coating with stable color, good brightness, flat coating and good solderability on the surface of the PCB board.
Immersion gold can make the PCB achieve good electrical conductivity during long-term use, and it also has environmental tolerance that other surface treatment processes do not have.
Immersion gold is very smooth, and the coplanarity is very good, which is suitable for the key contact surface. Also its gold solderability is excellent.
The ENIG process is complicated, and the gold surface is prone to black pad effects, which affects reliability.
ENEPIG has an extra layer of palladium between nickel and gold compared with ENIG. During the deposition reaction of replacement gold, the electroless palladium layer will protect the nickel layer and prevent it from being excessively corroded by replacement gold.
It’s good surface for gold wire bonding,It also can effectively prevent connection reliability problems caused by black pad defects. The cost is affordable.
Although nickel-palladium gold has many advantages, but palladium is expensive and is a scarce resource.
Compared with other surface treatment methods, ENEPIG has the advantages of stable durability, excellent solder resistance, good compatibility, high coating flatness, and suitable for high-density pads, so it can be applied to more precise PCBs. The welding performance is also better.
ENEPIG was first proposed by Intel, and now many BGA boards used in gold bonding wire on one side, and soldering on the other side.
The thickness requirements of the gold plating layer on both sides are different. Bonding requires a thicker gold layer, about 0.3 microns or more, while solder only needs about 0.05 microns.
If the gold layer is thicker, the bonding is good, but the solder strength is problematic. If the gold layer is thinner, the soldering is OK, but the bonding is not good. Therefore, the previous process was covered with dry film, and gold plating with different specifications was done twice to meet the requirements.
Now ENEPIG with the same thickness specifications on both sides can meet the requirements of bonding and soldering.The current specifications of palladium and gold film thickness are about 0.08 micron above, which can meet the requirements of bonding and soldering.
At present, More and more companies widely using ENEPIG on PCB board include: Microsoft, Apple, Intel,etc.