Advantages and disadvantages of FPC soft board surface treatment process

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Advantages and disadvantages of FPC soft board surface treatment process [Copy link]

1. Hot air leveling The general process of hot air leveling is: micro-etching → preheating → flux coating → tin spraying → cleaning. Advantages: longer storage time; after the PCB is completed, the copper surface is completely wetted (completely covered with tin before welding); suitable for lead-free welding; mature process, low cost, suitable for visual inspection and electrical testing Disadvantages: not suitable for wire binding; due to surface flatness problems, there are also limitations on SMT; not suitable for contact switch design. Copper will dissolve during tin spraying, and the board will be subjected to high temperature once. For particularly thick or thin boards, tin spraying is limited and production operation is inconvenient.

2. Organic solderability preservative (OSP)

The general process is: degreasing-->micro-etching-->pickling-->pure water cleaning-->organic coating-->cleaning, and process control is relatively easy compared to other surface treatment processes.

Advantages: simple process, very flat surface, suitable for lead-free soldering and SMT. Easy to rework, convenient production operation, suitable for horizontal line operation. Suitable for multiple treatments on the board (for example: OSP+ENIG). Low cost and environmentally friendly.

Disadvantages: Restriction on the number of reflow soldering (multiple soldering is thick, the film will be damaged, basically 2 times is no problem). Not suitable for crimping technology and wire binding. Visual inspection and electrical testing are inconvenient. N2 gas protection is required during SMT. SMT rework is not suitable. Storage conditions are required to be high.

3. Full board nickel gold plating

Advantages: Longer storage time > 12 months. Suitable for contact switch design and gold wire bonding. Suitable for electrical testing

Weaknesses: Higher cost, thicker gold. Additional design wires are required for conductivity when electroplating gold fingers. Because the thickness of gold is not uniform, when used in welding, the solder joint may be brittle due to too thick gold, affecting the strength. The problem of uniformity of the electroplating surface. The electroplated nickel gold does not cover the edge of the wire. It is not suitable for aluminum wire binding.

4. Immersion gold

The general process is: pickling and cleaning--> micro-etching--> pre-dip--> activation--> chemical nickel plating--> chemical immersion gold; there are 6 chemical tanks in the process, involving nearly 100 chemicals, and the process is relatively complicated.

Advantages: not easy to oxidize, can be stored for a long time, the surface is flat, suitable for welding fine gap pins and components with small solder joints. The first choice for PCB boards with buttons (such as mobile phone boards). It can be repeatedly reflowed without reducing its solderability. It can be used as a substrate for COB (Chip On Board) wiring.

Disadvantages: High cost, poor welding strength, because the use of electroless nickel plating process, prone to black disk problems. The nickel layer will oxidize over time, and long-term reliability is a problem.

5. Immersion Tin

Advantages: Suitable for horizontal line production. Suitable for fine line processing, suitable for lead-free welding, and especially suitable for crimping technology. Very good flatness, suitable for SMT.

Disadvantages: Good storage conditions are required, preferably not more than 6 months to control the growth of tin whiskers. Not suitable for contact switch design. The production process has high requirements for the solder mask process, otherwise the solder mask will fall off. When welding multiple times, it is best to use N2 gas protection. Electrical testing is also a problem.

6. Immersion Silver

Advantages: Simple process, suitable for lead-free welding, SMT. Very flat surface, low cost, suitable for very fine circuits.

Disadvantages: High storage conditions and easy to be contaminated. Welding strength is prone to problems (micro-void problems). It is easy to have electromigration and galvanic corrosion of copper under the solder mask. Electrical testing is also a problem.