Desmear

Desmear is a crucial process in the manufacturing of printed circuit boards (PCBs). It is employed after the drilling of holes in a PCB laminate and before the plating of these holes. The drilling process, typically done with mechanical drills, can leave behind a residue of epoxy resin and glass fibers from the drilled hole wall. This residue, known as "smear," can negatively impact the electrical conductivity and reliability of the through-holes.

The primary purpose of desmear is to remove this smear layer. This removal is essential to ensure a clean and conductive pathway between different layers of the PCB. Without effective desmear, plating materials may not adhere properly to the hole wall, leading to poor solder joints, intermittent electrical connections, and ultimately, PCB failure.

Several methods are used for desmear, with plasma desmear and chemical desmear being the most common. Plasma desmear utilizes a reactive gas plasma to etch away the smear layer. Chemical desmear involves immersing the PCB in a bath of chemicals that dissolve the epoxy and glass residue. The choice of desmear method depends on factors such as the type of PCB material, the required level of cleanliness, and cost considerations. Proper desmear is a critical step for producing high-quality, reliable printed circuit boards.