Printed circuit boards are electronic circuits boards created for mounting electronic components on a nonconductive board, and for creating conductive connections between them. The creation of circuit patterns is accomplished using both additive and subtractive methods. The conductive circuit is generally copper, although aluminum, nickel, chrome, and other metals are sometimes used.
PCB Manufacturing steps
Following are the steps involved in fabrication of PCB.
- Schematic Design and PCB Layout
- Base material cutting
- Through hole plating
- Layer film generation
- Solder resist film generation
- Legend printing film (optional)
- Spray developing
- Etching process
- Solder resist masking
- Legend printing (optional)
CAD System (Schematic Design and Layout)
Recommended software is Orcad. We are using it, since it is thought as a powerful tool in designing PCB layout. This software has enhanced features like improved interactive routing,user selectable track width, internal routing loops, PCB routing completion detector, preserving track angles while dragging, designing bottom layer layout (mirror has to done) just by flip and editing the board etc.,
PCB Shearing Machine (Base Material Cutting)
• Bench top guillotine type shearing machine to cut PCB’s and laminates
• Compact structure
• Central handle allows ease of cutting
CNC drilling machine(Drilling)
A computer automated, single spindle CNC machine is used which allows direct
processing of drill data or HP/GL data for PCB production(drilling) and milling/drilling of holes.Selection of drill bit is also manual and the drill bit moves to the corresponding coordinate to make a drill. Likewise drills of different dia can be made.
Film Developer (Film Generation)
After photo plotting, the individual PCB layer‘s film is produced by a developer machine. Then, under a light table the film is manually inspected for any track breaks, line shortages or missing of any track. Here we are developing films manually in a tray.
For PCB boards films must be produced according to the number of layers.
Powerful software tools generate a plot file, whose data control a photoplotter. Afterdeveloping the films, they have to be inspected under table lamp for any track breaks, line shortages or missing of any track.
Table top unit which serves as a negative making contact printer as well as illuminated art work table for circuit art work, taping and inspection of film and negatives
• User can directly make negative from1×scale artwork
• Workingarea:300mm×250mm(12″×10″) with diffused Light
• Pushbutton operated exposure
• 230V/50Hz,5ASocket required
Solder resist film
In order to ensure no shortings in the PCB due to formation of moisture, or due to spreading of solder leads, the complete board except the pads are to be soldered masked. This is done in CAD design tools and the photofilm is generated in the photoplotter. Then the photofilm is developed.
This is developed in order to ensure ease and fastness during soldering of components. This is also designed in CAD system and the film is generated in the photoplotter.
By this process the drilled and plated‐through boards are laminated by rolling under pressure a photo‐resist laminate on both sides of the board. This is used to laminate the entire board area with photoresist material. Here either
positive or negative photoresist material can be used for laminating the board. We generally use negative photo resist. Lamination is performed by rolling the photoresist coil under pressure on both sides of the moving board by heatable feed rollers. However rotational speed is adjustable as per requirement.
UV Exposure system (Exposing)
After properly aligning films on the photoresist laminated board, the board is exposed by a UV light on both sides in the UV exposure unit.
After fixing layout‐films exactly on both sides of the laminated board the light sensitive cover is exposed by a ultraviolet light in double‐sided drawer exposure unit with a vacuum system. After the exposure that part of the laminate, which is not protected by the layout film becomes etch‐resistent (if we use negative film &negative photo resist).
The exposed board is developed in a spray developer unit. The developer solution is sprayed on both sides of the board by a spray rotating system. Afterwards the rest of the non‐exposed laminate is removed by a rinsing process, whereas the exposed laminate is etch resistant and thus protects the circuit pattern against etching
Foam Etching – Fast single sided PCB etching. (Etching process)
After treating the board with aqueous alkaline solution it is subjected in foam etching center by hanging it into a foaming fluid (usually acids) to etch out the copper from the part of the PCB not exposed to UV. The copper part of the PCB
which is not exposed to UV gets softens and it is etched by acids. Now the board is ready with printed layout tracks, pads which are covered by photo resist. • Tank capacity: 20 Liters includes heater and air flow Compressor heater • Timer:0~4.0minutes • Electricpower:250V/50Hz,15Asocket required
In that process the UV non exposed copper is etched. Afterwards the etch resistant material over the tracks, pads of PCB is rinsed by means of a solvent attack.
Solder resist masking/Legend printing (optional)
In lab this is done manually by screen printing process
After getting the board,the board has been dried in oven where the temperature is curable.
Table topunit for curingof liquidphotoresist.
• Timer controlled heating system allows fast and efficient curing
• Complete metal construction
• PCBsize: 250mm×300mm (10″×12″).
• Heating: Finned heaters withthermostat controls
• Fan: For air circulation.
• Timer: Preset timer.
• Electricpower: 250V/50Hz,15A socket required
Other Tools Required
- Lens with lamp
- Computer and Printer
- Copper Clad Boards
- Ferric chloride
- Etch Resistant Inks
- PCB Drill bits
- Roll salt
- Flow coat