1. For PCBs, the common characteristic is resistance.

2. For instance, when discussing the characteristic impedance of a PCB, consistent transmission line conditions throughout typically indicate high quality.

3. What defines a controlled impedance circuit board? It is characterized by a uniform impedance across all transmission lines on the PCB, usually ranging between 25 and 70 ohms.

4. What primarily causes high impedance in a PCB? The quality of the PCB itself may not be the sole issue; over time, instability in performance, including impedance variations, can arise. What are the main factors contributing to this?

5. Please refer to the following academic analyses for further insight.

6. Impedance refers to both resistance and reactance parameters, as PCB circuits must account for conductivity and signal integrity post-installation of electronic components.

7. Thus, lower impedance values indicate better performance, ideally below 1 × 10^-6 ohms per square centimeter.

8. Furthermore, during production, PCBs must undergo copper electroplating with tin (or chemical plating) to ensure that resistivity is maintained, facilitating low overall impedance and meeting product quality standards.

9. Failure to achieve these standards can result in improper circuit board functionality.

1. In addition, within the electronics industry, the PCB circuit board’s tin plating process is a crucial factor affecting impedance. Electroless tin plating technology has gained widespread use, yet as part of the electronics sector, companies have engaged with this technology for over a decade. Nationally, only a limited number of companies can execute chemical tin plating (PCB or electronic tin plating) since this technology is relatively new in China, and the technological expertise among enterprises varies significantly.

2. Investigating the electronics industry reveals that the most critical weakness of the electroless tin layer is its susceptibility to discoloration (oxidation or wetting), which leads to increased welding resistance and consequently poor electrical conductivity or unstable performance across the entire board.

3. Reports indicate that tin plating was one of the first chemical research areas explored after graduating from Kunming University of Science and Technology in the early 1990s. Over the last decade, both institutions have received top accolades. Based on our thorough contact screening, experiments, and extensive endurance tests with numerous companies, we confirm that the Tongqian electroless tin layer is a pure tin layer with low resistance. This ensures high-quality conduction and soldering. It’s no surprise they guarantee the coating remains free of any protective or discoloring agents, maintaining its color for one year without bubbles, peeling, or permanent tin whiskers.

4. Subsequently, as the entire production industry matured, many later participants often resorted to imitation rather than original development. This has led to subpar performance in many products, affecting users’ electronic devices (the circuit board’s base or entire electronic products), primarily due to impedance issues. When unqualified electroless tin plating is applied to the PCB circuit board, the tin may not actually be pure tin (or pure metal). Instead, it can contain tin compounds, which are not true metal units, but rather metal compound oxides or halides. More directly, these could be non-metallic materials or a mixture of tin compounds and tin metal, often undetectable by the naked eye.

5. The primary circuit of the PCB is composed of copper foil, with solder joints connecting the copper foil to the tin-plated layer where electronic components are attached. In practice, the solder paste fuses the electronic components to the tin coating in a molten state, creating a single piece of metal with excellent conductivity. This highlights that the connection between electronic components and the copper foil at the PCB’s base occurs via the tin coating, making the purity and resistance of the tin coating essential. Before electronic components are connected, using instruments to detect impedance involves contact with the copper foil surface at the PCB’s bottom, linking back to the copper foil. Hence, the tin coating is pivotal in affecting impedance and, by extension, the overall performance of the PCB.

6. As we know, aside from pure metals, compounds are generally poor conductors of electricity, with some being non-conductive (which significantly impacts line distribution capacity or transmission capacity). Thus, the presence of conductive yet non-conductive tin compounds or mixtures in the tin plating layer can lead to higher resistivity levels, influenced by humidity and oxidation over time, impacting the signal transmission in digital circuits. Additionally, inconsistent characteristic impedance can affect both the circuit board and the overall machine performance.

7. Consequently, in contemporary PCB production, the coating material and performance at the PCB board’s base are the primary and most direct factors influencing the board’s characteristic impedance. However, due to coating aging and changes in wet electrolysis, the impact on impedance can become subtle and variable, primarily because it is not visible to the naked eye (including its changes) and is difficult to measure, as it fluctuates with time and environmental humidity, making it easy to overlook or misinterpret.

8. Therefore, understanding the root causes of high impedance and addressing coating issues is crucial to managing impedance effectively.