The difference between PCB immersion gold process and gold plating process
The difference between immersion gold board and gold-plated board
In the actual trial process, 90% of the gold boards can be replaced by immersion gold board instead of gold-plated board. The poor weldability of gold-plated board is its fatal shortcoming. In the process of use, because of the low conductivity of gold, it is widely used in contact circuits, such as keypads, gold finger boards, etc. The most fundamental difference between gold-plated board and immersion gold board is that gold plating is hard gold and immersion gold is soft gold. The following is an analysis from the electrical performance!
The difference between immersion gold board and gold-plated board
Why use gold-plated board
With the increasing integration of IC, the IC pins are more and more dense. However, it is difficult to flatten the thin pads with vertical tin spraying process, which brings difficulties to SMT mounting; in addition, the shelf life of tin spraying board is very short.
Gold-plated boards just solve these problems:
1 For surface mount technology, especially for 0603 and 0402 ultra-small surface mounts, 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 whole board gold plating is often seen in high-density and ultra-small surface mount processes.
2 In the trial production stage, due to factors such as component procurement, the board is often not soldered immediately after it arrives, but often has to wait for several weeks or even months before use. The shelf life of the gold-plated board is many times longer than that of the lead-tin alloy, so everyone is happy to use it. In addition, the cost of gold-plated PCB in the sample stage is almost the same as that of lead-tin alloy board.
However, as the wiring becomes denser and denser, the line width and spacing have reached 3-4MIL. Therefore, the problem of gold wire short circuit is brought about:
As the frequency of the signal becomes higher and higher, the situation of signal transmission in multiple plating layers due to the skin effect has a more obvious impact on the signal quality:
The skin effect refers to: for high-frequency alternating current, the current tends to flow on the surface of the wire. According to calculation, the skin depth is related to the frequency:
Other disadvantages of gold-plated boards are listed in the table of differences between immersion gold boards and gold-plated boards.
Why use immersion gold boards
To solve the above problems of gold-plated boards, PCBs using immersion gold boards have the following main features:
Because the crystal structures formed by immersion gold and gold plating are different, immersion gold will be golden yellow, which is yellower than gold plating, and customers are more satisfied.
Because the crystal structures formed by immersion gold and gold plating are different, immersion gold is easier to weld than gold plating, and will not cause poor welding and cause customer complaints.
Because there is only nickel gold on the pad of the immersion gold board, the transmission of the signal in the skin effect is on the copper layer and will not affect the signal.
Because the crystal structure of immersion gold is denser than that of gold plating, it is not easy to produce oxidation.
Because there is only nickel gold on the pad of the immersion gold board, it will not produce gold wires to cause micro-shorts.
Because there is only nickel gold on the pad of the immersion gold board, the combination of the solder mask on the circuit and the copper layer is more solid.
The engineering will not affect the spacing when making compensation.
Because the crystal structure formed by immersion gold and gold plating is different, the stress of the immersion gold board is easier to control, which is more conducive to the onding process for products with bonding. At the same time, because immersion gold is softer than gold plating, the immersion gold board is not wear-resistant for gold fingers.
The flatness and standby life of the immersion gold board are as good as those of the gold-plated board.