PCB

Printed Circuit Boards

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PCB Layout
The most common means of constructing an electronic circuit is on a printed circuit board or PCB. A pcb consists of a rigid sheet of material, typically fibreglass (GRP), clad with copper on one or both sides. A pattern of conducting traces is formed in the copper layer thus generating the circuit. The pattern defining the traces is defined in an acid resistant paint ("resist") this paint can be applied via a screen printing process, but is more typically a photosensitive compound, that is selectively removed after being exposed to light through the "artwork", Holes are drilled in the pcb to take components and for "vias" to allow connection from the top trace to the bottom trace. On double sided boards, plated through holes (PTH) are the norm, these holes connect the top trace to the bottom.

PCB Manufacture Cinereus farms out all of its PCB manufacturing usually to BEC. There is usually space available on each panel to include additional boards, and you may be able to "piggyback" your boards on our next run.

Normally the PCB design is generated on a computer, and then emailed to a PCB manufacturing company such as BEC, a week or so later, the completed boards arrive on the doorstep.
There are a variety of processes and vendors available, and the costs, quality, lead time vary accordingly.
In House- engraving/ isolation: A small computer controlled router removes the unwanted copper, allowing prototype boards to be manufactured in less than a hour. The negative aspects are the lack of a solder mask and overlay, no plated through holes, no tinned pads and limited to 20mil tracks and gaps.
In house etching: The artwork can be generated by laser printer on transfer film, then a precoated ("Riston") board is exposed, developed and etched in ferric chloride, holes are then hand-drilled. Can be very cheap for one offs, and thus favoured by hobbyists. On the downside, can be a messy and time consuming process, and not very accurate and again, no PTH, overlays or tinning. Acetronics (Sydney) supply all the materials equipment required for this form of processing.
Single board prototyping vendors: These vendors will generate an artwork from your file, and cut PCB's to be slightly larger than your artwork, then use semi-automated processes to develop (or screen print), etch, drill and route the board. Disadvantages are the board to board variability, and the poor registration for double sided boards.
Full panel vendor: These manufacturers use a fully automated process and manufacture standard size panels. As all panels are the same size, it is easy to keep the process tuned up, and there is no need to change the machine setups for each run. Consequently excellent tolerances can be held, and the turn around time is short. Where only one small board is required the cost per board is excessive.

PCB Assembly

Once the PCB's are manufactured , the components need to be loaded onto the board, and there are many ways to do this. Generally small components are attached before the larger ones.
Surface mount components can be placed with a "pick and place" machine , this is generally economical for more than 10 large boards, but requires a "solder paste mask" and a "glue mask" (around $200).
The SMD components can also be hand placed. Once placed the components need to be soldered, typically by Infra-Red reflow (Much like an electric griller). Small batches can be hand soldered.
The larger through hole components are then placed (usually by hand, but robotic insertion is feasible in larger quantities). The leads are then trimmed. The boards are then "wave" soldered, i.e held just above a bath of molten solder while a wave is induced in the surface.
The boards are then washed (e.g. with alchohol or citric acid based solutions) to remove flux residues.
Finally open frame (i.e. unwashable) components (pots, switches, some connectors, transformers, speakers, microphones) are attached.