Characteristics difference between immersion gold PCB and gold plating PCB

I: Immersion gold PCB board and electric gold PCB board

1. Immersion gold board and chemical gold board are the same process product, electric gold board and flash gold board are also the same process product. In fact, it is just a different name from different people in the PCB industry. Immersion gold board and electric gold board are more common in the title of the mainland China PCB manufacturers, while the chemical gold board and the flash gold board are more commonly referred to by the Taiwan PCB manufacturers.

2. Immersion gold/chemical gold PCB is generally called chemical nickel gold PCB or chemical nickel immersion gold PCB. The growth of nickel/gold layer is generated by chemical deposition; electro gold PCB /flash gold PCB is generally called electroplated nickel gold PCB or flash gold PCB. The generation of the nickel/gold layer is plated by DC electroplating.

3. Refer to the table below for the difference in mechanism between electroless nickel gold plating (immersion gold) and electroplated nickel gold (gold plating):

	Color Appearance	Solderability	Signal Transmission	Quality	Engineering
Gold plating PCB	Gold with little white	Normal, accidently pseudo solder	conductor skin effect, not good for high frequency signal	1.  Gold surface is easy oxidize 2. Gold wire may cause short 3. Bonding stress with soldermask is not good	No need Line Compensation, suit for small space
Gold immersion PCB	Gold	good	conductor skin effect is small	1.  Gold surface is not easy oxidize 2. No gold wire 3. Bonding stress with soldermask is good	Need  Line compensation

II: Why do not use "HASL" for high end PCB?

1. As the integration level of IC becomes higher and higher, IC pins become denser. The vertical spray tin process is difficult to flatten the thin pads, which brings difficulty to the SMT process; in addition, the shelf life of the HASL PCB is very short. The immersion gold board just solves these problems

2. For the surface mount process, especially for 0603/0402 or ultra-small surface mount chips, because the flatness of the pad is directly related to the quality of the solder paste printing process, it has a decisive influence on the quality of the subsequent reflow soldering, so the gold immersion is common in high-density and ultra-small surface mount processes.

3. In the PCB prototype production stage, due to factors such as component procurement, it is often that the board is not soldered immediately, but it is often used for several weeks or even months. The shelf life of the gold-plated board is longer than that of lead-tin board, so everyone is willing to use it. Besides, the cost of the gold-plated PCB in the sample stage is almost the same as that of the HASL PCB board. But as the wiring becomes denser, the line width and spacing have reached 3-4mil, gold plating process also brings about the problem of short circuit of gold wire.

As the frequency of the signal gets higher and higher, the skin effect of signal transmission in the multi-plated layer has more obvious influence on the signal quality:
The skin effect refers to: high frequency alternating current, the current will tend to concentrate on the surface of the wire to flow. According to calculations, skin effect depth is related to frequency.