Printed circuit boards are the backbone of all electronic devices, from simple watches and calculators to sophisticated systems such as computer and radar systems. For the newbies, a PCB directs electric current to electric components through copper pathways on its surface. This guide explains the various aspects employed in pcb circuit board manufacturing.
Material
While printed circuit boards can be fabricated from different materials, the FR4 is commonly used. FR4 is a form of glass fiber loved for its high degree of stability over a wide range of temperatures. Additionally, FR4 is relatively cheap and does not break down easily. Where designers want to achieve high performance radio frequencies, the PTFE material is used. Copper is the preferred material for the direct current pathways.
PCB Manufacturing Process
PCB fabricators, like Avanti Circuits, may not necessarily be the circuit designers. Where fabrication is being outsourced, circuit designers have to communicate with the fabricators to present their manufacturing demands. This helps designers avoid software compatibility issues and reduce the chances of propagating error to the fabrication phase.
Design Phase
A number of software may be used for the design of printed circuit boards. These include OrCAD, Eagle, KiCad, Pads, and Altium Designer among others. Designers have to get a go-ahead on which software to use, from which they send their design for approval. Extended Garber software is mostly used for sharing designs. To ensure designs can endure threshold tolerances, fabricators test the designs using Design for Manufacture check software.
Generating the Film
A circuit can only be printed on the glass fiber substrate after passing all preliminary tests. At the heart of film printing is a dedicated printer called the plotter, which is essentially a laser printer. Plotters are accustomed to their delicate work to deliver prints of exceptional accuracy. This results to a photo negative from which the copper circuitry is developed. Film circuits are printed using black ink, with the clear portions denoting non-conductive areas.
Interestingly, pcb circuit board manufacturing is done in layers where each layer receives its own film. A double-layer circuit board requires four sheets, two for the film and the rest for the solder mask. These sheets must be used in harmony for perfect alignment of the PCB to be achieved. Guiding holes punched into the sheets help manufacturers achieve perfect alignment.
Preparing the Inner Layers
Once the film is created, it is used to map out where the copper will go in the final substrate. This step is precedent by mapping out the film onto a copper foil. Essentially, the final PCB consists of a glass fiber and a laminate that receives the copper. The substrate is thoroughly cleaned and decontaminated to get rid of any dirt which may lead to broken circuits.
A layer of photo sensitive material is applied to the cleaned substrate upon which the copper pathways go. This photo sensitive layer is meant to harden when exposed to ultra violet light. The substrate board with its photo sensitive layer is then exposed to selective ultra violet light that traces the circuit design. Once the light is passed, the photo resist hardens on the copper underneath. The black-inked film helps prevent light from reaching areas that are not meant to harden. The board is then washed using an alkaline solution to remove the unhardened photo-resist material.
Removing Unwanted Copper
With the desired circuit safely concealed under the photo-resist material, the board is washed using a powerful chemical to get rid of exposed copper. The clean board is then punched with registration holes to help align the inner and outer layers. Finally, the product is scanned using optical devices to compare it with the original file received from the circuit developers. The process of manufacturing circuit boards may vary slightly depending on the required PCB properties.