表面处理

表面处理是指应用于高密度互连（HDI）印制电路板（PCB）基板上裸露铜迹线和焊盘的最终涂层或处理。它起到多种作用：在存储和组装过程中保护底层铜免受氧化和腐蚀，为元件连接提供可焊表面，并确保在高频和细间距应用中可靠的电气性能。在具有微孔、细线路和高元件密度的HDI PCB中，表面处理的选择和质量对良率、可靠性和信号完整性至关重要。

工作原理涉及通过化学或电化学过程在铜表面施加一层薄而均匀的材料。该层作为屏障，防止环境因素（如湿气和氧气）氧化铜，形成不导电或可焊性差的氧化层。在焊接过程中，表面处理要么溶解到焊料中（形成冶金结合），要么提供可润湿的表面供焊料附着，从而形成可靠的电气和机械连接。不同的表面处理（如ENIG、HASL、OSP）通过特定的化学反应（如浸金于镍上或有机聚合物形成）来实现这些特性。

The working principle involves applying a thin, uniform layer of material over the copper surfaces through chemical or electrochemical processes. This layer acts as a barrier against environmental factors (like moisture and oxygen) that could oxidize the copper, forming a non-conductive or poorly solderable oxide layer. During soldering, the surface finish either dissolves into the solder (forming a metallurgical bond) or provides a wettable surface for the solder to adhere to, creating reliable electrical and mechanical connections. Different finishes (e.g., ENIG, HASL, OSP) operate on specific chemical reactions—such as immersion gold over nickel or organic polymer formation—to achieve these properties.