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Design007-Mar2020

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18 DESIGN007 MAGAZINE I MARCH 2020 As many of you probably already know, PCB etching seems like a sim- ple task on the surface—the selective removal of material using an etching agent. However, quite a few things can go wrong during this process, such as over-etching, copper areas that detach from the board, issues with etching so- lution, and even accidental removal of critical components. Considered by many to be somewhat of an art form, PCB manufacturers work hard to cre- ate a better etching process (remember acid traps?). Adhering to best practice and continuous improvement is a must to help avoid issues with your finished board. In this column, we share our de- sign tips for a better etching process. Etching Process Overview Once all of the layers are laminated together, the through-holes are drilled, the copper is plated (both electroless and electroplated), and the outer layer images are applied, it is time to physi- cally create all of the traces and pads for a circuit board via the etching pro- cess (Figure 1). Etching defines the distinctive routes of a PCB. It is also the process that tests the quality of a design by answering the design questions that will determine its functionality. Did you leave enough space? Are your traces wide enough? PCB manufacture etching is a reductive pro- cess, not an additive process. The board starts with a consistent layer of copper throughout, and the etching process removes all unwanted copper. Now, if you think that sounds waste- ful, don't worry; the copper removed during etching is easily captured and recycled. Remember that we start the PCB process with a fully copper-clad panel. After coating it in a light-sensitive polymer, we project high-in- tensity UV through an image of the PCB design that you carefully composed. A photoresist lay- er covers the areas where we want to remove The Seven-year Etch Connect the Dots by Bob Tise and Matt Stevenson, SUNSTONE CIRCUITS Figure 1: New copper for plating.

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