In the PCB surface treatment process , there are several treatment processes that we often confuse: gold plating, immersion gold and nickel palladium gold, what are the differences between them?
1. Gilded
Gold plating uses real gold, and even if it is only plated in a thin layer, it already accounts for nearly 10% of the cost of the entire circuit board. Gold plating uses gold as the coating, one is for the convenience of soldering, and the other is for corrosion protection; even the gold fingers of memory sticks that have been used for several years are still as shiny as ever.
Advantages: strong electrical conductivity, good oxidation resistance, long life; dense coating, relatively wear-resistant, generally used in welding and plugging occasions.
Disadvantages: high cost, poor welding strength.
2. Chemical gold/immersion gold
Electronized nickel immersion gold (ENIG), also known as electroless nickel gold, immersion nickel gold, referred to as electroless gold and immersion gold. Immersion gold is to coat the copper surface with a thick layer of nickel-gold alloy with good electrical properties through chemical methods, and can protect the PCB for a long time. The deposition thickness of the inner layer of nickel is generally 120~240μin (about 3~6μm), and the deposition thickness of the outer layer of gold is generally 2~4μinch (0.05~0.1μm). 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.
Advantages: 1. The surface of the PCB treated with immersion gold is very smooth, and the coplanarity is very good, which is suitable for the key contact surface. 2. The solderability of immersion gold is excellent, and the gold will quickly melt into the molten solder to form a metal compound.
Disadvantages: The process is complicated, and the process parameters need to be strictly controlled to achieve good results. The most troublesome thing is that the immersion gold-treated PCB surface is prone to black disk effects, which affects reliability.
3. Nickel palladium gold
Compared with nickel-gold, nickel-palladium-gold (ENEPIG) has an extra layer of palladium between nickel and gold. 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. ; Palladium is fully prepared for immersion gold while preventing corrosion caused by displacement reactions. The thickness of nickel deposition is generally 120~240μin (about 3~6μm), the thickness of palladium is 4~20μin (about 0.1~0.5μm); the thickness of gold deposition is generally 1~4μin (0.02~0.1μm).
Advantages: a wide range of applications, while nickel-palladium-gold is relatively heavy gold, which can effectively prevent connection reliability problems caused by black disk defects.
Disadvantages: Although nickel-palladium gold has many advantages, palladium is expensive and is a scarce resource. At the same time, like immersion gold, its process control requirements are strict.