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I've always been fascinated by the tiny electronic components that power modern devices. As I learned more about electronics, I discovered the world of surface mount devices (SMDs). These small surface-mount assemblies allow engineers to integrate more computing power into ever-shrinking gadgets. In this beginner's guide, I will walk you through the basic concepts of SMD components. You'll learn about the common types of SMDs, how to recognize them, how they're soldered, and how they compare to old-fashioned through-hole components. Let's get started on what it means.
Surface mount components or surface mount devices, as the name suggests, are components that are designed to be mounted directly to the surface of a PCB. This is in contrast to traditional through-hole components, which are characterized by leads that pass through holes in the circuit board. one of the major advantages of SMDs is their small size. Because there are no bulky leads, surface mount components fit snugly on the surface of the board. This allows the PCB to fit more components in less space. For example, smartphones would not be able to achieve their miniature size without utilizing surface mount components.
Ease of automation - Surface mount device components can be quickly placed and soldered by automated pick-and-place assemblers.
Improved Signal Integrity - With no leads, alignments are shorter and parasitic effects are reduced.
Lower Costs - More compact PCBs mean lower material costs.
Miniaturization - Surface mount components are essential for mounting complex electronics into miniature packages.
Chip Resistors
Resistors limit the current in a circuit. The size and various values of these components determine their resistance to current.
Chip Capacitors
Capacitors for storing and discharging electrical energy are available in ceramic, tantalum and electrolytic types. Each type is suitable for different applications based on their specific characteristics.
Chip Inductors
Inductive components gather energy in the magnetic field created by current flowing through them. These devices are often used in filter circuits, oscillators and power supply implementations.
SMD Diodes
SMD diodes are used in rectification, signal demodulation, and switching applications to facilitate the flow of current in one direction while blocking the flow of current in the opposite direction.
SMD Transistors
Transistors amplify or switch electronic signals and are the basic building blocks of electronic devices. There are different types of transistors, including bipolar junction transistors (BJTs) and field effect transistors (FETs).
SMD Integrated Circuits (ICs)
Integrated circuits are the backbone of countless electronic products that we use every day. Inside these tiny black chips lies a world of complex circuitry - logic gates, microcontrollers, amplifiers, and many other components densely packed together.
SMD Crystal Oscillators
These components use piezoelectric crystals to generate a precise and stable frequency, and are commonly used in microcontrollers and communication devices.
SMD Connectors
SMD connectors are used to make electrical connections between PCBs or electronic components and include a variety of types such as plugs, sockets and board-to-board connectors.
Chip Switches
MD switches are critical in electronic devices, interrupting or establishing electrical connections within compact devices. They are found in a variety of electronic products in momentary and switching configurations.
Soldering SMD components
Soldering through-hole parts is easy with a soldering iron. But surface mount devices require a different approach. Their pads and leads are too small for a soldering iron to reach. Instead, SMD soldering relies on heating the entire board in an oven.SMD soldering typically uses two PCB soldering techniques:
Reflow Soldering
In reflow soldering, solder paste is first applied to the PCB pads using a stencil or syringe. Next, components are placed onto the solder paste deposit by means of a pick-and-place machine. Finally, the PCB enters the reflow oven. The board passes through a heated zone, which increases in temperature enough to melt or "reflow" the solder paste. As the solder liquefies, it is sucked up by capillary action onto the component leads and PCB pads. When the board leaves the oven, the solder cools rapidly and hardens, forming a mechanical and electrical bond.
Wave Soldering
For high volume manufacturing, a conveyorized wave soldering process is common. First, one side of the PCB is loaded with SMD components and solder paste. After reflow of that side, the bottom side passes through a wave soldering system. This involves transferring the board onto a container containing liquid solder. A pump creates a tilted wave that briefly touches the underside of the PCB. Wave soldering instantly welds through-hole component leads and bottom-side alignments. Precise speed control prevents excess solder buildup. Wave soldering increases efficiency when combining through-hole components and SMDs on a single board.
We've covered the basics of identifying and soldering surface mount components. How do they compare to traditional through-hole parts? Let's review the advantages and disadvantages of each technology.
Advantages of SMD
Smaller size - allows for PCB miniaturization and denser designs.
Improved performance - lower parasitic components due to shorter alignments.
Automation - pick and place assembly is efficient.
Lower cost - smaller SMD boards save material when produced in high volume.
Disadvantages of SMD
More difficult hand soldering - Hot air station or reflow skills required.
Higher start-up costs - SMD assembly requires pick-and-place and reflow equipment.
Tighter tolerances - more susceptible to soldering defects and bridging.
Repairability - Desoldering and replacing SMDs is very challenging.
Benefits of Through-Hole Components
Easier Hand Soldering - Large leads are easily soldered with a soldering iron.
Component Availability - Wider selection of generic through-hole parts.
Easier replacement - it's easier to desolder damaged parts.
Better heat resistance - leads provide some protection from heat damage.
Disadvantages of Through-Hole Components
Larger size - less efficient utilization of PCB area compared to SMDs.
Lower component density - limits the level of miniaturization.
Parasitic components - longer leads add unwanted inductance and capacitance.
Limited automation - manual insertion and soldering is time consuming.
More susceptible to mechanical stress - longer leads are more susceptible to damage from shock/vibration.
Working with surface mount devices can seem intimidating at first, but once you understand the basics, it becomes much easier. The most common SMD components are resistors, capacitors, and integrated circuits. Familiarizing yourself with identifying these different part types is a critical first step in familiarizing yourself with surface mount assembly and design. If you have any additional questions, please contact GreensTone electronics, www.greenpcba.com .
