Printed circuit board .
A printed circuit board . mechanically supports and electrically connects electronic components using conductive tracks, pads and other features etched from copper sheets laminated onto a non-conductive substrate. Components – capacitors, resistors or active devices – are generally soldered on the PCB. Advanced PCBs may contain components embedded in the substrate.
PCBs can be single sided one copper layer, double sided two copper layers or multi-layer outer and inner layers. Conductors on different layers are connected with vias. Multi-layer PCBs allow for much higher component density.
FR-4 glass epoxy is the primary insulating substrate. A basic building block of the PCB is an FR-4 panel with a thin layer of copper foil laminated to one or both sides. In multi-layer boards multiple layers of material are laminated together.
Design
Initially PCBs were designed manually by creating a photomask on a clear mylar sheet, usually at two or four times the true size. Starting from the schematic diagram the component pin pads were laid out on the mylar and then traces were routed to connect the pads. Rub-on dry transfers of common component footprints increased efficiency. Traces were made with self-adhesive tape. Pre-printed non-reproducing grids on the mylar assisted in layout. To fabricate the board, the finished photomask was photolithographically reproduced onto a photoresist coating on the blank copper-clad boards
Copper patterning
The first step is to replicate the pattern in the fabricator’s CAM system on a protective mask on the copper foil PCB layers. Subsequent etching removes the unwanted copper.
a conductive ink can be ink-jetted on a blank This technique is also used in the manufacture of hybrid circuits.
Post time: Jan-08-2017