PCB MANUFACTURING
PCB MANUFACTURING
Printed Wiring Board
The PCB physically supports and electrically links electrical or electronic components using conductive paths, pads and other features etched from one or more layers of copper laminated on and/or between sheet layers of non-conductive substrate.
Net List
It is a simple text file which have 2 sections:
- Part List
- Wire/Net List
Part list has the component details and its description, while the wire list contains information about the pin numbers of the components, which pin connected to which wire and to which IC pin.
Important Points for PCB manufacturing
- Pads are slightly bigger than the pin size.
- Pin and pad should have such a distance that the solder paste can easily go between them for proper soldering.
- The pin and pad dimensions are called toe and heel size.
- To create a footprint of the components, send the datasheets to the PCB layout department so that they can make the footprints using the mechanical dimensions given in the datasheets.
- If there is a single pin net, it means there is some problem with the schematic as a net should at least have 2 pins.
- If any part is on the other page of the same schematic diagram, then simply assigning net alias will not work, it should be shown as double arrows which means they are connected together even if they are on different pages.
- If there is a problem or error in the schematic diagram then it will show a long number starting with -N1123435, indicating that there is an error.
- The Layout department is provided with BOM, net list and PDF of the schematic.
- Component notation in silk screen is always written left to right or bottom to top, so that the customer can read it easily and it is the standard followed in the industry.
Placement Part
- For placement of the items, an outline or size is required.
- Fiducials are placed on the PCB after generating the netlist.
- Mounting holes are also placed which normally have 125 mils diameter.
- Mounting holes are placed for alignment (normally 4 in number), for fixing/gripping the board and the chassis in which the PCB would be fitted.
- Mounting holes are normally non plated but can be plated also depending on the usage.
- They are basically stiffeners so that the board remains straight and does not move.
- Fiducials are reference points for pick & place machines. They help remove tolerance.
- X-Y file provides the coordinates to the machine for drilling and these fiducials help the machine know where to start from by using a laser light sensor to detect.
PKI/RKI
- It is Package keep in or route keep in.
- It is a border placed on the PCB which is normally 25mils away from the actual PCB.
- It acts as a border and no trace/route or component is allowed to go near or cross this area or edge.
Design Rules for PCB Manufacturing
- Before completing the designing phase, a DRC (Design Rule Check) is done to make sure that there are no errors in the design.
- If there is any violation, then the software will highlight by showing specific symbols.
- Instructions are provided to the software department to highlight the errors present.