PCB Chemical Etching - China PCBA Supplier

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A very complex procedure called PCB etching is essential to the creation of printed circuit boards. It efficiently removes copper from the PCB, aiding in the creation of the final circuit pattern. The etching procedure gets the board ready for the final phases of manufacture, even if there are still a lot of additional steps to do before the board is complete.

The process of etching a printed circuit board (PCB) to generate the desired circuit pattern involves removing undesired copper from the PCB. The most used technique for etching PCBs is the application of a chemical solution, like ferric chloride.

After applying a photoresist coating to the PCB, the exposed portions are forced to solidify by exposure to UV light via a film mask. After that, the board is submerged in the chemical solution, which removes the exposed copper and leaves the intended circuit pattern in its place.

Chemical etching is usually done with ammonium persulfate or ferric chloride. For PTH (plated-through holes), additional steps of electroless deposition are done after the holes are drilled, then copper is electroplated to build up the thickness, the boards are screened, and plated with tin/lead. The tin/lead becomes the resist leaving the bare copper to be etched away.

The simplest technique, immersion etching, involves immersing the board in an etching solution, such as ferric chloride, and is typically employed by hobbyists and small-scale producers. The etching process takes longer than mass production processes. The etching rate can be accelerated in the bath by adding heat and stirring. To agitate the solution and expedite the etching process, air is circulated through the etchant bath during bubble etching. Since spray etching is faster than splash etching, splash etching is no longer a viable commercial method. Instead, a motor-driven paddle is used to splash boards with etchant. During the spray etching process, pumps circulate the etchant solution after nozzles spread it over the boards. Etching rates can be consistently controlled, resulting in high production rates, by adjusting the nozzle pattern, flow rate, temperature, and composition of the etchant.

Some etchants have a capacity of up to 150 grams of copper per liter of solution; as more copper is eaten from the boards, the etchant becomes saturated and less efficient. Etchants can be replenished to regain their efficacy for commercial purposes, and the dissolved copper can be extracted and marketed. The disposal of used etchant, which is hazardous and caustic because it contains metal, is an important consideration when doing small-scale etching.

Copper on any surface that isn't shielded by a resistor gets eliminated by the etchant. When the etchant targets the thin copper edge beneath the resist, a phenomenon known as "undercut" takes place, which can narrow conductor widths and result in open circuits. To avoid undercut, the etch time must be carefully controlled. Metallic plating can "overhang" when employed as a resist, which, in cases when the traces are closely spaced, can result in short circuits between them. After etching, the board can be wire-brushed to eliminate the overhang.