Why is the PCB board plated with gold?

Why is the PCB board plated with gold

As the integration level of IC becomes higher and higher, the number of IC pins becomes denser and denser. However, the vertical HASL process is difficult to flatten the fine pads, which brings difficulties to SMT placement. In addition, the shelf life of the HASL board is very short.

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    Why is the PCB board plated with gold?

    Gold-plated PCB
    Gold-plated PCB

    1. For the surface mount process, especially for 0603 and 0402 ultra-small surface mount, because the flatness of the pad is directly related to the quality of the solder paste printing process, it has a decisive impact on the quality of the subsequent reflow soldering. Therefore, gold plating on the entire board is often seen in high-density and ultra-small surface mount processes.

    2. In the trial production stage, due to the influence of component procurement and other factors, it is often not to solder the board as soon as it arrives, but to wait for several weeks or even months before using it. The shelf life of the gold-plated board is longer than that of the lead board.

    In addition, the cost of gold-plated PCB in the sample stage is almost the same as that of lead-tin alloy board.

    But as the wiring becomes denser, the line width and spacing have reached 3-4MIL.

    Therefore, the problem of short circuit of the gold wire is brought. As the frequency of the signal increases, the signal quality is more significantly affected by the signal transmission through multiple plating layers due to the skin effect.

    The skin effect refers to the high-frequency alternating current, and the current will tend to flow on the surface of the wire. According to calculations, the skin depth is frequency dependent.

    Features of immersion-gold PCBs

    Immersion-gold PCB
    Immersion-gold PCB

    In order to solve the above problems of gold-plated boards, PCBs using immersion gold boards mainly have the following characteristics:

    1. Because the crystalline structure formed by immersion gold and gold plating is different, immersion gold will be more golden yellow than gold plating, and customers are more satisfied.

    2. Immersion gold is easier to weld than gold plating, and will not cause poor welding and customer complaints.

    3. Because the immersion gold board only has nickel gold on the pad, the signal transmission in the skin effect is on the copper layer and will not affect the signal.

    4. Because the crystal structure of immersion gold is denser than that of gold plating, it is not easy to produce oxidation.

    5. Because the immersion gold board only has nickel gold on the pad, it will not produce gold wires and cause micro shorts.

    6. Because the immersion gold board only has nickel gold on the pad, the combination of the solder mask on the circuit and the copper layer is stronger.

    7. The project will not affect the spacing when making compensation.

    8.Because the crystal structure formed by immersion gold and gold plating is different, the stress of the immersion gold plate is easier to control.

    9. The flatness and standby life of the immersion gold plate are as good as those of the gold-plated board.

    For the gold plating process, the tinning effect is greatly reduced, while the tinning effect of immersion gold is better. Unless the manufacturer requires, most manufacturers will now choose the immersion gold process .

    How to do it a Immersion gold ENIG on production of bare PCB

    Surface treatment types

    In general, the surface treatment of PCB is as follows:

    Gold plating (electroplating gold, immersion gold), silver plating, OSP, HASL (leaded and lead-free).

    Regarding the advantages and disadvantages of several methods of surface treatment, each has its own advantages and disadvantages!

    In terms of gold plating, it can make the PCB store for a long time, and it is less affected by the external environment temperature and humidity changes (compared to other surface treatments), generally it can be stored for about one year; HASL surface treatment is second, OSP is the third. A lot of attention should be paid to the storage time of the two surface treatments in the ambient temperature and humidity.

    Generally speaking, the price of immersed silver is high, and the storage conditions are more stringent. It needs to be packaged in sulfur-free paper! And the storage time is about three months! In terms of the tin effect, immersed gold, OSP, and HASL are almost the same. The manufacturer mainly considers their cost performance.

    FAQ-about PCB

    • Corrosion Resistance
    • Conductivity
    • Durability
    • Excellent heat protection
    • Ease of coating application
    • No fretting degradation

    Gold conducts electricity very efficiently (an obvious requirement for PCB applications) It can carry small amounts of current, essential for today's electronic devices. Other metals can be alloyed with gold such as nickel or cobalt. It does not tarnish or corrode, making it a reliable connection medium.

    Gold plating (electroplating gold, immersion gold), silver plating, OSP, HASL (leaded and lead-free).

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