Fabrication of PCB Prototype
Before the manufacture and PCB assembly, the first step is fabrication of its prototype. For this, the professionals and even DIY developers can use any number of methods. One of the standard procedures related to this is as follows.
- 1. Cleaning of board’s copper surface
- 2. Application of etch resist for copper to use
- 3. Use copper etchant for removing unwanted copper
- 4. Stripping resist off from etched board
- 5. Application of protective coat to prevent oxidation of copper
Preparation of artwork
The kind of artwork required to make PCBs will depend upon other steps related to its fabrication process. Artwork should be 1:1 to the final circuit board. In the past, it consisted of art in the literal sense made with crepe black tape, red Rubylith, or blue or red vinyl tape. Board fabricators separate and reduce board original PC artwork 2xs or 4xs in one ratio one negatives, or/and positives. Physical existence of this artwork is no longer present nowadays except on photo plotters. Modern computers offer high-resolution outputs generating directly usable one ratio one artwork in laser outputs. Alternatively, one can use it as an artwork to expose photoresist.
You can perform this procedure in prototype PCB fabrication using copper etchants in any number. However, when you were using tin resist the common etchant is ammonium persulphate. Other etchants tend to attack tin. Etching occurs in tray or tank, resistant to the etchant in use. The commonest in this regard is polyethylene with acrylic and polypropylene too in use with etchants. Obviously, metal doesn't lend itself to use in such circumstances. It is possible to agitate the etchant using air bubbles, rock it in tray, or go for recirculation using a pump. Also, spray in continuous streams or rub on using a sponge.
You can directly apply some resists such as silkscreen, printer laser toner, or pen with etch resistant properties. PCB metallic resist fabrication properties masks copper area marked for removal as the first step, this is followed by tin plating or copper plating of the area you need to retain. Tin plating makes it resistant to etch. However, before you undertake etching it is important to strip off the original photoresist.
Direct application of photoresist types occur on cleaned copper with sandwiching of positive-negative circuit images followed by exposure to ultraviolet light. This development is similar to that of photograph followed by rinsing processes. Inclusion of silkscreen signifies an additional step. It involves photographic creation of silkscreen followed by etch resist screening upon bare copper. For bulk work, this is an inexpensive process even if it lacks resolution features associated with photoresist direct method.
Copper has quick oxidation properties. However, such oxidized copper doesn't lend itself easily to soldering. To deal with this limitation,fabrication and PWB assembly services apply a thin tin coating to exposed copper surface. When one uses the resist process for metal, electroplating of tin upon copper occurs before etching.
About The Author
David Fischer is an Engineer and has a special interest in the world of circuit board. He is also a part of the lab testing teams in various companies. He loves to write and share his extensive knowledge & experience in this field. He highly recommends BestProto.net for building electromechanical and prototype PCB.