One of the methods performed for PCB fabrication is etching. It is the chemical process of taking out the excess copper from the plated board. A mask should be placed in order to avoid removing the parts of the copper that need to stay after the etching process. These parts that stay on the plated board are the remnants that hold electric current between the devices.
In PCB fabrication, there are various techniques to prepare the plated board before going through the etching process:
1. Direct Draw
The direct draw etching technique makes use of a resist pen to manually draw the circuit. It may also utilize dry transfers or specialty tapes where the users can layout their circuit traces right onto the board’s copper surface. The pen method depends on the water resistant attribute of the ink and the imperviousness of the plastic tapes both prevent the etchant from reaching the copper underneath. Thus, aside from the copper around the layout, all are etched away. This is actually the fastest method of transferring a circuit pattern to the plated board. The downside of this technique, however, is that it is hard to accurately place the traces, particularly when IC packages are used in the design. In addition, because the ink does not apply evenly, there is a threat that the traces are going to be etched away considering that the etchant can reach the copper. Making a mistake would mean having to start all over again. This is why direct draw method can only utilized to make super simple, low-definition printed circuit boards.
Most professionals recommend this etching method for PCB fabrication. In this process, a board is coated with a resist substance that sets up whenever subjected to Ultra Violet light. To be able to produce this kind of board, the user need to create a positive ultra violet translucent artwork film of the opaque layout where a circuit trace should appear, and clear where a circuit trace should not appear. As soon as the positive photo film is constructed from the artwork, stick it onto the refined board, and expose it to the ultraviolet light. This light passes through the clear sections of the film and programs the photo resist. Then, immerse the board into a special fluid that develops the film and take out the refined photo resist. The remaining resist takes the form of the artwork that presents the circuit. The good thing about this approach is that it is more accurate and the traces are neat. Plus, the artwork film can be reused again and again to produce more boards.
It is definitely impossible to obtain a good quality board without having good artwork. For this reason, it is crucial to attain the best quality possible during this period. To be able to achieve this, it is essential to have a clear sharp picture with an incredibly solid unintelligible opaque black.
These days, PCB fabrication artwork will, more often than not, be drawn using either an appropriate sketching or graphics package, or a unique printed circuit board CAD program.
The artwork should be printed in such a way that the printed side comes in contact with the surface of the PCB when exposing. This is to prevent getting blurry edges. In practice, this signifies that if the user makes a design for the board as viewed from the opposite side, the solder side layer needs to be printed the ‘right’ way round. The top side, on the other hand, of the double-sided board should be printed in a mirror manner. The quality of the artwork in PCB fabrication is extremely influenced by both the media used as well as the output device.
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