PCB Introduction and Categories
PCB, short for printed circuit
board, is the supplier of electronic components and electronic connections. The
key advantage of PCBs is to greatly reduce the errors of routing and assembly
and to increase the degree of automation and fabrication efficiency.
PCBs can be classified into
different types according to different classification standards. Based on the
number of layers, PCBs can be classified into single-layer PCBs, double-layer
PCBs and multi-layer PCBs. Based on the substrate material, PCBs can be
classified into rigid PCBs, flexible PCBs and flex-rigid PCBs. Based on
application fields, PCBs can be divided into low-frequency PCBs and
high-frequency PCBs. With the development of technology and the advent of new
material, some special types of PCBs come into being, such as metal core PCBs, smt
PCBs carbon-film PCBs, etc.
Following lines share major types
of circuit boards and quickly review their advantages and disadvantages.
1. Single-layer PCBs
Single-layer PCBs are the most
basic type of PCB. They contain only one conductive layer and as such constrict
their use to simple low density designs. Accordingly, they are low cost and
well suited to simple and high volume products.
2. Double-layer PCBs
Double-layer PCBs probably are
the most common type of PCB. They allow for the routing of traces around each
other by jumping between a top and bottom layer by way of vias. The ability to
cross paths from top to bottom greatly increases the PCB designer's flexibility
in circuits designing and lends itself to greatly increased circuit densities.
This type of board is relatively low cost, but only allows an intermediate level
of circuit complexity and does not lend itself to electromagnetic interference
reduction techniques.
3. Multi-layer PCBs
Multi-layer PCBs further increase
the complexity and density of PCB designs by adding additional layers beyond
the top and bottom layers seen in a double-sided configuration. With the
availability of over thirty layers in multilayer PCBs configurations,
multi-layer PCBs allow designers to produce very dense and highly complex
designs. Quite often the extra layers in these designs are used as power
planes, which both supply the circuit with power and also reduce the
electromagnetic interference levels emitted by designs. Lower EMI levels are
achieved by placing signal levels in between power planes. It's also of note
that increasing the number of power planes in a PCB design with increase the
level of thermal dissipation a PCB can provide, which is important in high
power designs.
4. Aluminum Backed PCBs
Typically used in high power
applications, aluminum packed PCBS are the ultimate solution to
thermal heat dissipation issues. Consisting of a thin circuit layer adhered to
a thick aluminium backing by way of a thermally conductive dielectric, aluminium
backed designs can keep high power components cool under heavy loads. Aluminum
backed PCBs are often found in high power LED products and switching power
supplies. This kind of PCBs also offer high levels of mechanical rigidity and
low levels of thermal expansion, making them ideal for applications with very
tight mechanical tolerances. Finally, aluminum backed PCBs are perfect for
applications where the PCB is going to be subject to a great deal of mechanical
stress.
5. Flexible PCBs
Flexible PCBs present the perfect solution to creating reliable
and repeatable interconnections between electronics boards. They allow for
complicated interconnections to be printed rather than made using discrete
conductors. The result is a greatly reduced level of complexity in device
assemblies and more reliable operation. Flexible PCB designs can also be very
complex, with very high signal trace densities and multilayer configurations
available to designers.
6. Rigid Flexible PCBs
Rigid-flex PCBs allow for
the use of flexible PCBs for the majority of a design while protecting a
section of the PCB design that is not intended to be bent. This is of great
benefit when you want to use a flexible PCB as the basis of your design. Often
flexible PCBs are designed to include surface mount devices in a portion of the
flexible board. This section will then be reinforced with a rigid backing to
protect the ICs from flexing during use. Flexible PCBs are also much lighter
and can fit into tighter housing than their traditional counter parts. Using
flexible PCBs, three dimensional designs can also be accommodated in a single
PCB. When size and weight are a point of emphasis, flexible PCBs are a great
starting point.
7. Flex-rigid PCBs
Flex-rigid
designs allow for an interconnection flexible PCB to be permanently connected
to a rigid multilayer PCB board. This type of configuration is used when a
design calls for very complex PCB, but the designer wants to reduce the
complexity of final product assembly by including the flexible interconnection
PCB in the fabricated PCB. As such, using a flex-rigid PCB allows for the
complete design to be ready upon receipt from the PCB
fabricator. Flex-rigid designs also allow for the creation
of three dimensional designs and can include multiple rigid and flexible
sections.
