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Gold plating and gold plating are both common PCB board surface treatment, the manufacturing process is different, but also applies to different PCB products.
Electroless Nickel Immersion Gold, also known as immersion gold, in English is Electroless Nickel Immersion Gold, abbreviated as ENIG, usually called electroless nickel immersion gold or simply as electroless gold or immersion gold. Immersion gold is the use of chemical methods in the PCB board copper surface first deposited a layer of nickel, and then in the nickel layer deposited a layer of gold, the advantage is that it does not need to use electroplating, the process is relatively simple.
Gold Plating
Gold plating, in short, is to be gold plated on the copper skin of the circuit board, but if the gold and copper in direct contact, there will be electron migration diffusion of the physical reaction (potential difference relationship), so it must be plated a layer of nickel as a barrier layer, and then plated to the top of the nickel gold plating, so gold plating, the actual name of the nickel plated gold should be called electroplating. Electroplated gold can be divided into electroplated hard gold and electroplated soft gold. The difference between hard gold plating and soft gold plating lies in the composition of the final layer of gold plated on. When plating gold, you can choose to plating pure gold, you can also choose to plating alloy. Because the hardness of the alloy is relatively hard, while the hardness of pure gold is relatively soft, so the industry usually plating alloy is called electroplating hard gold, electroplating pure gold is called electroplating soft gold.
The process of hard and soft gold plating:
Hard gold: pickling → electroplating nickel → pre-gold plating (flash gold) → electroplating gold-nickel or gold-cobalt alloy
Soft gold: pickling → electroplating nickel → electroplating pure gold
Electroplated hard gold is an electroplated alloy, i.e., an alloy consisting of electroplated gold and other metals, such as gold-nickel or gold-cobalt alloy. Because of the hardness of hard gold, electroplated hard gold is suitable for places that require force and friction. The most common application of hard gold plating in the PCB industry is for the gold fingers of plugs and sockets, graphics cards and memory sticks.
Soft gold plating is pure gold plating. Because the hardness of soft gold is relatively soft, so the electroplated soft gold is generally used for COB (Chip On Board) above the wire plate Pad, or mobile phone button contact surface.
With the advancement of gold plating technology and cost advantage, soft gold plating has been gradually replaced by gold plating or nickel-palladium gold.
Differences between gold plating and gold plating
1. The principle and process is different from the gold plating process without electricity, is a chemical replacement reaction. Gold first through a chemical reaction in the PCB board copper surface plating a layer of 3 ~ 5um thick nickel-phosphorus alloy (common nickel layer thickness specification 3um Min), and then use gold salts and nickel layer reaction, plated on a relatively thin layer of gold, usually only 0.025 - 0.15um (common gold thickness specification 0.025um Min). Electroplating gold is an electrochemical reaction. PCB board in the gold bath plating solution acts as a ‘cathode’, after the power supply is switched on, the gold ions move under the action of the current and turn into gold atoms on the surface of the PCB board, forming a gold layer. The thickness of electroplated gold is generally 0.1 - 5 microns, common specification is 0.76um Min. The purity of electroplated gold is over 99%, there are insertion and removal of demand for PCB boards, such as gold finger boards, the need to control the hardness of the gold surface, usually requires 100KN Min.
2. Each has its own advantages and disadvantages, according to customer requirements
Gold plating: more cost-effective, good solderability.
Advantage: flatter surface, good weldability; stable signal transmission, suitable for high-frequency circuits; simple equipment, low cost, high efficiency, widely used in mass production of consumer electronics products.
Disadvantages: the gold layer is relatively thin, easy to wear, oxidation; can not transmit high current; process control is not good, there may also be an impact on the welding of the ‘black disc’ problem (‘black disc’ can be referred to the PCB board Javanese effect Galvanic Effect ( Galvanic effect on PCBs (gold-plated boards)).
Electroplated gold: long life, high cost Advantages: thick gold layer, good abrasion resistance, anti-friction properties and anti-oxidation properties.
Suitable for: aerospace, high-end servers and other products with high protection requirements.
Gold layer thickness: can be adjusted as needed, good conductivity, can withstand high currents, power module class PCB board commonly used gold-plated treatment.
Disadvantage: higher cost.3. Appearance of different gold plating gold layer is thinner, the colour is light gold, the bottom colour is vaguely transparent to the bottom layer of nickel layer of matte feeling.
Electroplated gold
gold layer is thicker, the colour is darker gold, the gold is more intense and full, and may even be slightly yellow-red tone. Gold-plated thick gold layer of good wear resistance, long life, long-term use of the gold colour is still obvious yellow.