Surface Mount Technology in Printed Circuit Boards
Just what is surface mount technology? Prior technology of printed circuit board design and fabrication consisted mostly of components situated on the board and connected to conductors through holes and typically soldered in place. This through-hole methodology requires obvious manufacturing steps of drilling holes in the board material, inserting leads through those holes properly and consistently, and connecting them in place securely through soldering processes.
While many of these fabrication functions are today highly automated to provide quality and efficiency, they are nonetheless steps in the manufacturing process that require attention to detail and introduce potential for flaws and quality issues when not executed with exacting precision.
Surface mount technology (SMT) began to be widely used in the 1980s with the introduction of improved manufacturing processes and surface mount devices (SMDs). Nearly every electronic device that contains printed circuit boards and is mass produced today includes some level of SMT-manufactured boards. SMT boards are typically smaller through the very nature of smaller SMD components that can be positioned in a higher density on the board.
SMT vs. Through-Hole PCB Fabrication
SMT manufacturing of PCBs provides a number of advantages over the previous through-hole technology:
- Smaller components – SMDs are not only smaller themselves, but they also greatly reduce the space and processes needed for connecting to the board without the need for leads, placement and drilling of holes, and soldering. SMDs are connected directly to the board surface. SMD components are typically one quarter to one tenth the size and weight of through-hole devices – an obvious advantage for PCB designers and the devices they will be used in.
- Higher density of components – this results in smaller boards or even fewer boards.
- Construction facilitates the mounting of components on both sides of the board.
- Manufacturing efficiency – reduced cost through simplified setup and reduction of hole drilling operations.
- Reduced cost – many SMD components are less expensive than their leaded counterparts.
- Reliability – SMT fabrication is generally less susceptible to impact from vibration or shaking.
- SMD use can reduce resistance and inductance.
- Smaller board size and shorter paths can improve performance.
There are, of course trade-offs or disadvantages in SMT board construction:
- Construction of prototypes or manual fabrication is more difficult.
- Board repair of components is also more challenging, not easily done by manual means.
- Use of breadboard materials for construction is not feasible with SMDs.
- SMD construction is not suitable when there are requirements for high power or large high-voltage parts such as in power circuits.
- Thermal cycling potting compounds can damage SMD solder connections.
- Through-hole fabrication is less vulnerable to damage from exposure to harsh environments such as repeated shock or vibration. Since leads actually pass through holes and are soldered, the connections are less likely to fail than surface-mounted devices.
- Capital outlay for SMT equipment is considerable.
- SMT design requires more advanced skills than traditional through-hole methods.
- Through-hole still retains a strong foothold in prototyping and testing.
- Not all components are available as SMDs. In such cases through-hole design will remain the only alternative.
SMT Application in Practice
SMT technology is utilized nearly exclusively in the manufacturing of today’s electronic devices. SMT provides the ability to generate mass-produced, smaller, lighter boards with fewer fabrication steps and less setup time, reducing cycle times and fabrication complexity. This makes the resulting PCBs less expensive to produce and more cost-effective for use in electronics or other products.
Modern computer aided manufacturing capabilities increasingly automate placement of components that previously required manual or assisted operations. SMD manufacturers also continue to develop components that simplify assembly through reduced size and ease of placement and connection to board surfaces. Some applications require a hybrid use of through-hole and SMT boards to take advantage of the particular benefits of each technology. The two technologies can co-exist side-by-side without issues.
Automated processes, reduced size and weight, and simplified fabrication have combined to make SMT board manufacturing the primary method utilized in today’s electronic devices. Sophisticated equipment required to manufacture SMT PCBs can be a significant investment, resulting in the use of outsourced manufacturing for many companies needing SMT boards.