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Immersion silver process printing is indispensable in the manufacture of PCB circuit boards, but the immersion silver process can also cause defects or scrap. The formulation of preventive measures needs to consider the contribution of chemicals and equipment to various defects in actual production in order to avoid or eliminate defects and improve the yield rate.
PCB board immersion silver process
The prevention of the Javani effect can be traced back to the copper plating process in the previous process. For high aspect ratio holes and micro-vias, a uniform plating thickness helps eliminate the hidden dangers of the Javani effect.
Excessive corrosion or side corrosion during film stripping, etching, and tin stripping processes will all promote the formation of cracks, and microetching solutions or other solutions will remain in the cracks. Nevertheless, the problem of the solder mask is still the main reason for the Javani effect. Most of the defective PCB boards with the Javani effect have side corrosion or the solder mask peeling off. This problem mainly comes from exposure and development. Process. Therefore, if the solder mask shows a "positive foot" after development, and the solder mask is completely cured, then the Javanni effect problem can be almost eliminated.
To get a good immersion silver layer, the position of the immersion silver must be 100% metallic copper, each tank solution has a good through hole capacity, and the solution in the through hole can be exchanged effectively. If it is a very fine structure, such as HDI board, it is very useful to install ultrasonic or jet in the pretreatment and immersion bath. For the production management of the immersion silver process, controlling the micro-etching rate to form a smooth, semi-bright surface can also improve the Javani effect. For original equipment manufacturers (OEMs), designs that connect large copper surfaces or high-aspect-ratio through holes with thin lines should be avoided as much as possible to eliminate the hidden dangers of the Javanni effect.
For chemical suppliers, the silver immersion liquid should not be very aggressive. It is necessary to maintain a proper pH value, control the immersion speed and generate the expected crystal structure, and achieve the best corrosion resistance with the thinnest silver thickness. Corrosion can be reduced by increasing the density of the coating and reducing the porosity. The use of sulfur-free material packaging, while sealing to isolate the plate from contact with the air, but also to prevent the sulfur entrained in the air from contacting the silver surface. It is best to store the packaged boards in an environment with a temperature of 30°C and a relative humidity of 40%. Although the shelf life of immersion silver PCB boards is very long, the first-in first-out principle must be followed when storing.
Shielding methods in high-speed PCB design
The transmission rate of high-speed PCB design and wiring systems is steadily accelerating, but it also brings a certain anti-interference vulnerability. This is because the higher the frequency of transmission of information, the increase in signal sensitivity, and their energy is getting weaker and weaker. At this time, the wiring system is more susceptible to interference.
High-speed PCB layout design
Interference is everywhere. Cables and equipment will interfere with other components or be seriously interfered by other sources of interference, such as: computer screens, mobile phones, electric motors, radio relay equipment, data transmission and power cables, etc. In addition, potential eavesdroppers, cybercrime, and hackers are increasing because their interception of UTP cable information transmission will cause huge damages and losses.
Especially when using a high-speed data network, the time required to intercept a large amount of information is significantly lower than the time required to intercept low-speed data transmission. The twisted pair in the data twisted pair can rely on its own twisting to resist external interference and crosstalk between the pairs at low frequencies, but at high frequencies (especially when the frequency exceeds 250MHz), only rely on Wire pair twisting can no longer achieve the purpose of anti-interference, and only shielding can resist external interference.
The function of the cable shielding layer is like a Faraday shield, interference signals will enter the shielding layer, but not into the conductor. Therefore, the data transmission can run without failure. Since shielded cables have lower radiation emission than unshielded cables, the network transmission is prevented from being intercepted. The shielded network (shielded cables and components) can significantly reduce the electromagnetic energy radiation level that may be intercepted when entering the surrounding environment.
