In any electronic product, the most essential component is the printed circuit board (PCB), whether it is a complex mobile phone or low-cost electronic device. In the product development cycle, one of the biggest issues is design cost management, and the most neglected and expensive element of BOM is the PCB. PCB cost is relatively higher than that of any other component used in the circuit, so by reducing its size, a designer can reduce the product size and production cost as well.
This article discusses design techniques for the reduction of PCB size through tradeoffs and other possible solutions.
Multi-layer PCBs
Routing takes up the most space in a PCB. In the prototype stage, designers should use a single or at most two-layered PCB board while testing the circuit. The circuit is mostly made using surface mount devices (SMD), meaning the designer must use a double-layered PCB board. Double-layered board design provides the surface access to all the elements and for traces routing, gives the board spaces. The surface space of the board increases as the layers of the board are increased more than two layers, for instance, four or six layers. But there is a problem: the complexity of the circuit increases with increasing the number of layers that makes it difficult to repair, test and rework.
Consequently, multi-layered PCB boards (mainly four-layered) are possible only if the board is testing properly in the prototype phase. Other than the size of the board, time for designing the circuit is much shorter than designing it in a bigger one- or two-layered board.
But there are some common tradeoffs. The cost of any multi-layered printed circuit board is much higher than that of single-layered boards. Therefore, before converting a single- or double-layered board to a multi-layered board (mainly four) it is important to have an estimate of cost purpose. However, an increase in the number of layers could significantly affect the board size.
Component package selection
In the circuit design, one of the major things is component selection. The same components with different packages are available in the electronics market. For instance, a resistor of rating 0.125 W can be available in different packages, such as 0402, 0805, 1210 and so on.
Mostly, the PCB prototype prefers to use larger components as compared to the general ones. As larger components are relatively easier to handle, solder, test and replace. For example, the prototype of the PCB board uses 0805 or 1210 resistor packages and a non-polarized capacitor of higher clearances. During the production stage, these larger components can be replaced by a smaller package having the same ratings as that of the larger components, and board space can be compressed. The package size of these components can be reduced as well.
But the question is which package to choose? Using packages smaller than 0402 is recommended because of the handling limitations of the standard pick and place machines available in the market for production purposes.
Power rating is another problem with smaller components. Packages smaller than 0603 could handle relatively lower current than that of 0805 or 1210. So, proper components should be selected with great care and consideration. In such a case, if the smaller package cannot be used, the footprint can be edited and the component pad could be shrunk as much as possible. By changing the footprints, the designer can squeeze things tighter. However, because of design tolerances, the available default footprint is called a common footprint that can hold any package version.
New compact connectors
The connector is another space-eating element. It takes larger board space, and higher diameter pads are used by footprints as well. If you have tolerance in the current and voltage ratings then it is beneficial to change the connector type. Manufacturing companies offer different sizes of the same type of connectors, thus selecting the right size of connectors could save the board space and cost.
Resistor networks
Series pass resistors are always required for the protection of microcontrollers from higher current flow, mostly in microcontroller-based designs. Depending on the type of board, more than eight or sometimes more than 16 resistors are needed to use as series pass resistors. These resistors consume considerable space on the PCB board. To solve this issue, network resistors came into play. The space of four or six resistors could be saved by using a simple package-based resistor network of 1210.
Circuit boards with heavy copper
If a large amount of space on the PCB board is allocated to high current traces or thermal management, the board can be shrunk by the use of heavier copper as it can help reduce the trace width. The thickness of the copper layer is usually 1 oz, so doubling it to 2 oz allows shrinking the width of the trace by half with no effect on the current capacity. Two ounces is quite common and can be handled easily. In the industry, heavy copper is somewhat between 4 oz to 10 oz. So, upgrading from 1 oz to 2 oz is quite a realistic situation to power issue on the board being shrunk.
Stacked packages
Many designs are available in the market in which multiple transistors or more than two MOSFETs are required. Using stacked packages could save space as compared to adding up single transistors or MOSFETs.
Many options are also available that use multiple elements in a single package. For instance, the availability of dual or quad MOSFET packages saves a lot of space on the board as they take the space of only one.
Conclusion
The above-mentioned points are a few possible options that are useful for reducing the size of the PCB board. However, the selection of the exact way relies upon the application or specific circuit design. These methods apply to almost all the components and help save space on the PCB board. The additional advantage is that sometimes the cost of these components is relatively lower than that of individual components.
