PCB and connector commonly used gold plating process
Many users have been confused about the "chemical gold", "plated gold" and "flash gold" on the PCB board, and some people are always unable to distinguish between "hard gold" and "soft gold" Many people often ask, how thick should the connector be gold-plated? Konnra connector engineers will focus on introducing you to the differences between PCB and connector commonly used gold-plating process and their characteristics, so that everyone will no longer be confused in this regard.
Gold plating process
In the PCB and connector industry, the plating process related to us. It is mainly divided into two categories: electrolytic plating (hereinafter referred to as electroplating) and chemical plating.
Electroplating: Electroplating refers to the process of performing an electrolytic reaction in a solution by the action of external current to deposit a uniform and dense metal or alloy on the surface of the substance to be coated. The electroplating reaction principle is the galvanic reaction. During electroplating, the anode undergoes an oxidation reaction, dissolves and loses electrons, and metal atoms become cations; the cathode undergoes a reduction reaction, and metal anions obtain electrons to form a plating layer.
Electroless plating: In the aqueous solution does not rely on the external power supply, only rely on the reducing agent in the plating solution for chemical reduction reaction, so that the metal ions are continuously reduced to metal atoms deposited on the surface of the substrate to form a metal plating process. Typical is the PCB surface treatment process: ENIG.
Comparison of electroless plating and electroplating
The biggest difference between electroless plating and electroplating is that no external current is required. The thickness of the electroless plating layer is uniform, and the pinhole rate is low.
2. PCB common gold plating process
Nickel plating
Electrolytic Nickel/ Gold is the originator of the PCB surface treatment process, which has appeared since the PCB appeared. It is that the surface conductor of the PCB is plated with a layer of nickel and then a layer of gold. The principle is to dispose the nickel solution and gold (commonly known as gold salt) dissolved in the chemical liquid, soak the pre-processed circuit board in the electroplating cylinder (nickel plating cylinder/gold plating cylinder) and apply current to the circuit board. Nickel/gold plating is generated on the surface of copper foil. Electroplated nickel gold is widely used in electronic products because of its high hardness, wear resistance, and low oxidation.
ENIG
The full name of ENIG is Electroless Nickel/Immersion Gold.
The advantage is that you can attach "nickel" and "gold" to the copper skin without using a complicated power supply device (rectifier), and its surface is smoother than electroplated nickel/gold. This increasingly shrinking electronic parts and requirements are flat High-degree components are particularly important.
The ENIG process generally goes through the processes of pickling, micro-etching, activation, chemical nickel plating, cleaning, and gold immersion. The key step is the auto-catalytic nickel plating on the copper pad, generally through parameters such as temperature, pH, and additive concentration. To control the thickness of the nickel plating layer; then use the activity of the fresh nickel plating to immerse the nickel-plated pad in acidic gold water, and replace the gold from the solution to the surface of the solder layer by chemical substitution reaction, and part of the surface Nickel is dissolved in gold water, so as long as the replaced gold completely covers the nickel layer, the replacement reaction will automatically stop, and finally after cleaning the pad surface of dirt and chemical residues, the ENIG process ends.
Gold Flash
The term "Flash Gold" is derived from the English Flash, which means fast gold plating, commonly known as water gold plating. In fact, it is a "pre-gold plating" procedure for electroplating hard gold. It uses a larger current and a thinner gold-containing liquid bath. First, a thinner, but thinner gold plating layer is formed on the surface of the nickel layer to facilitate Subsequent electroplating of gold-nickel or gold-cobalt alloys can be more convenient.
Because the "gold flash" does not have the following gold plating process, its cost is much cheaper than that of real gold plating, but also because its "gold" layer is very thin, it generally cannot effectively cover all the nickel layers under the gold layer, so It is relatively easy to cause the problem of oxidation after the circuit board is stored for a long time, which further affects the solderability.
About "Hard Gold" and "Soft Gold"
The difference between "hard gold" and "soft gold" lies in the difference between "alloy" and "pure gold", because "pure gold" is actually softer, and "alloy" doped with other metals is harder and resistant to friction, so the more Pure gold is relatively softer.
Hard gold plating is actually a plating alloy (containing cobalt, nickel and other elements, element content ≤0.2%), so the hardness will be relatively hard, suitable for use in places where stress and friction are required, and is generally used as a connector in the electronics industry Contact surface, the contact point of the edge of the circuit board (commonly known as "gold finger" place).
Because of the principle of replacement, ENIG's gold plating is "pure gold", so it is often classified as a "soft gold".
3. Connector gold plating process
In most electronic connectors, the terminals must be surface-treated, generally referred to as electroplating. There are two main reasons: One is to protect the base material of the terminal reed from corrosion. Most connector reeds are made of copper alloys, which usually corrode in the environment of use, such as oxidation and vulcanization. The second is to optimize the performance of the terminal surface, establish and maintain the contact interface between the terminals, especially the film layer control. In other words, making it easier to achieve metal-to-metal contact.
Several things to consider when gold plating:
1. a layer of nickel
Nickel plating has a blocking effect on the migration or diffusion between gold and copper, the latter being particularly preferred. The bottom layer of nickel is the primary factor to be considered for precious metal plating. With a positive oxide surface, nickel provides an effective barrier layer that blocks the substrate and the pores, thereby reducing the potential for pore corrosion; and provides a hard layer under the precious metal plating The supporting layer, which improves the plating life.
2. Porosity
In the electroplating process, gold nucleates on many stains exposed on the surface, forming a porous electroplated surface. The porosity of the gold coating has a certain relationship with the thickness of the coating. Below 0.38 μm, the porosity increases rapidly. Above 0.76 μm, the porosity is very low. Porosity is also related to substrate defects such as inclusions, laminations, stamping marks, incorrect stamping cleaning, etc.
3. Wear
The wear or life of a plated surface depends on two characteristics of surface treatment: friction coefficient and hardness. The coefficient of friction decreases and the life of the surface treatment increases. Electroplated gold is usually hard gold to improve the wear resistance of gold.
4. Summary: How to choose gold plating process
Judging from the current surface treatment methods of many circuit boards, the cost of electroplating nickel gold is relatively higher than other surface treatment methods (such as ENIG, OSP), so it is now less used unless special purposes, such as sliding The need for contact elements (such as gold fingers); however, in terms of current circuit board surface treatment technology, the electroplated nickel-gold coating has good anti-friction ability and excellent oxidation resistance or other surface treatment processes are unmatched .
ENIG is currently the most widely used in circuit board surface treatment. However, ENIG also has its own weaknesses, especially for dense QFP/SOP/small PAD or BGA, if the process control is not good, the nickel surface will be corroded and the pad blackened (also known as black pad Black Pad Nickel corrosion).
Most of the connector terminals use gold plating technology, and the thickness of gold plating depends on product life and environmental application requirements. Due to the high cost of gold, choosing the appropriate thickness is often a concern.
Gold plating process
In the PCB and connector industry, the plating process related to us. It is mainly divided into two categories: electrolytic plating (hereinafter referred to as electroplating) and chemical plating.
Electroplating: Electroplating refers to the process of performing an electrolytic reaction in a solution by the action of external current to deposit a uniform and dense metal or alloy on the surface of the substance to be coated. The electroplating reaction principle is the galvanic reaction. During electroplating, the anode undergoes an oxidation reaction, dissolves and loses electrons, and metal atoms become cations; the cathode undergoes a reduction reaction, and metal anions obtain electrons to form a plating layer.
Comparison of electroless plating and electroplating
The biggest difference between electroless plating and electroplating is that no external current is required. The thickness of the electroless plating layer is uniform, and the pinhole rate is low.
Nickel plating
Electrolytic Nickel/ Gold is the originator of the PCB surface treatment process, which has appeared since the PCB appeared. It is that the surface conductor of the PCB is plated with a layer of nickel and then a layer of gold. The principle is to dispose the nickel solution and gold (commonly known as gold salt) dissolved in the chemical liquid, soak the pre-processed circuit board in the electroplating cylinder (nickel plating cylinder/gold plating cylinder) and apply current to the circuit board. Nickel/gold plating is generated on the surface of copper foil. Electroplated nickel gold is widely used in electronic products because of its high hardness, wear resistance, and low oxidation.
The full name of ENIG is Electroless Nickel/Immersion Gold.
The advantage is that you can attach "nickel" and "gold" to the copper skin without using a complicated power supply device (rectifier), and its surface is smoother than electroplated nickel/gold. This increasingly shrinking electronic parts and requirements are flat High-degree components are particularly important.
The ENIG process generally goes through the processes of pickling, micro-etching, activation, chemical nickel plating, cleaning, and gold immersion. The key step is the auto-catalytic nickel plating on the copper pad, generally through parameters such as temperature, pH, and additive concentration. To control the thickness of the nickel plating layer; then use the activity of the fresh nickel plating to immerse the nickel-plated pad in acidic gold water, and replace the gold from the solution to the surface of the solder layer by chemical substitution reaction, and part of the surface Nickel is dissolved in gold water, so as long as the replaced gold completely covers the nickel layer, the replacement reaction will automatically stop, and finally after cleaning the pad surface of dirt and chemical residues, the ENIG process ends.
The term "Flash Gold" is derived from the English Flash, which means fast gold plating, commonly known as water gold plating. In fact, it is a "pre-gold plating" procedure for electroplating hard gold. It uses a larger current and a thinner gold-containing liquid bath. First, a thinner, but thinner gold plating layer is formed on the surface of the nickel layer to facilitate Subsequent electroplating of gold-nickel or gold-cobalt alloys can be more convenient.
Because the "gold flash" does not have the following gold plating process, its cost is much cheaper than that of real gold plating, but also because its "gold" layer is very thin, it generally cannot effectively cover all the nickel layers under the gold layer, so It is relatively easy to cause the problem of oxidation after the circuit board is stored for a long time, which further affects the solderability.
About "Hard Gold" and "Soft Gold"
The difference between "hard gold" and "soft gold" lies in the difference between "alloy" and "pure gold", because "pure gold" is actually softer, and "alloy" doped with other metals is harder and resistant to friction, so the more Pure gold is relatively softer.
Hard gold plating is actually a plating alloy (containing cobalt, nickel and other elements, element content ≤0.2%), so the hardness will be relatively hard, suitable for use in places where stress and friction are required, and is generally used as a connector in the electronics industry Contact surface, the contact point of the edge of the circuit board (commonly known as "gold finger" place).
Because of the principle of replacement, ENIG's gold plating is "pure gold", so it is often classified as a "soft gold".
3. Connector gold plating process
In most electronic connectors, the terminals must be surface-treated, generally referred to as electroplating. There are two main reasons: One is to protect the base material of the terminal reed from corrosion. Most connector reeds are made of copper alloys, which usually corrode in the environment of use, such as oxidation and vulcanization. The second is to optimize the performance of the terminal surface, establish and maintain the contact interface between the terminals, especially the film layer control. In other words, making it easier to achieve metal-to-metal contact.
Several things to consider when gold plating:
1. a layer of nickel
Nickel plating has a blocking effect on the migration or diffusion between gold and copper, the latter being particularly preferred. The bottom layer of nickel is the primary factor to be considered for precious metal plating. With a positive oxide surface, nickel provides an effective barrier layer that blocks the substrate and the pores, thereby reducing the potential for pore corrosion; and provides a hard layer under the precious metal plating The supporting layer, which improves the plating life.
2. Porosity
In the electroplating process, gold nucleates on many stains exposed on the surface, forming a porous electroplated surface. The porosity of the gold coating has a certain relationship with the thickness of the coating. Below 0.38 μm, the porosity increases rapidly. Above 0.76 μm, the porosity is very low. Porosity is also related to substrate defects such as inclusions, laminations, stamping marks, incorrect stamping cleaning, etc.
3. Wear
The wear or life of a plated surface depends on two characteristics of surface treatment: friction coefficient and hardness. The coefficient of friction decreases and the life of the surface treatment increases. Electroplated gold is usually hard gold to improve the wear resistance of gold.
4. Summary: How to choose gold plating process
Judging from the current surface treatment methods of many circuit boards, the cost of electroplating nickel gold is relatively higher than other surface treatment methods (such as ENIG, OSP), so it is now less used unless special purposes, such as sliding The need for contact elements (such as gold fingers); however, in terms of current circuit board surface treatment technology, the electroplated nickel-gold coating has good anti-friction ability and excellent oxidation resistance or other surface treatment processes are unmatched .
ENIG is currently the most widely used in circuit board surface treatment. However, ENIG also has its own weaknesses, especially for dense QFP/SOP/small PAD or BGA, if the process control is not good, the nickel surface will be corroded and the pad blackened (also known as black pad Black Pad Nickel corrosion).
Most of the connector terminals use gold plating technology, and the thickness of gold plating depends on product life and environmental application requirements. Due to the high cost of gold, choosing the appropriate thickness is often a concern.
The thickness of the coating directly affects the life of the connector. Related insertion tests have been carried out in the industry to demonstrate the relationship between the thickness of the coating and the life. A test data uses a terminal with a diameter of 0.635 cm, a friction distance of 1.27 cm, and a positive force of 100 g per cycle.
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