Surface Mount Technology, SMT Includes:
What is SMT SMD packages Quad flat pack, QFP Ball grid array, BGA Plastic leaded chip carrier, PLCC
Surface mount devices, SMDs, or SMT components come in a variety of packages. As virtually all mass produced electronics uses surface mount technology: surface mount components are of great importance
These surface mount components come in a variety of packages, most of which are standardised to make the manufacture of the PCB assemblies using automated equipment much easier.
Printed circuit board with a variety of SMT packages as well as through hole mounted connectors
Some of the most widely used components are surface mount resistors and surface mount capacitors. These SMD resistors and capacitors these come in small rectangular packages, some of which are absolutely minute.
Additionally there is a variety of different SMT packages for integrated circuits dependent upon the level of interconnectivity required, the technology being used and a variety of other factors.
A number of other components are available, some of which are in standard packages, but others, because of their very nature need specialised packages with non-standard outlines.
When the surface mount packages were developed, one of the considerations that was given was that of component handling. As the whole aim of surface mount technology was that it should facilitate automated PCB assembly, the packages needed to be designed so that they could be manipulated on pick and place machines easily.
The SMT package styles have been developed to provide easy handling during the shipping and stock stages of the supply chain, and then by the pick and pale machines used for PCB assembly.
Ensuring the components can be handled easily at all stages, ensures that manufacturing costs are reduced, and the quality of the assembled PCBs and the final equipment is as high as possible.
Often the very smallest components are held loose in a hopper and these are fed down a tube and picked out as required.
Larger surface mount components like resistors and capacitors as well as many surface mount diodes and transistors may be held in a tape on a reel. The reel consists of a tape within which the components are held and a second tape is loosely stuck onto the back As the machine uses components, so the retention tape is pulled off exposing the next component to be used.
Other components like dual in line surface mount ICs may be held in a tube from which they can be removed as required, and then under gravity the next one slides down.
Very large ICs, possibly quad flat packs, QFPs and plastic leaded chip carriers, PLCCs may be held in what is called a waffle pack which is placed onto the pick and place machine. Components are successively removed as they are required.
Industry standards are used to provide a large degree of conformity across the industry. Accordingly the sizes of most SMT components conform to industry standards like the JEDEC specifications.
The JEDEC Solid State Technology Association is an independent semiconductor engineering trade organisation and standardisation body. The organisation has over 300 member companies, many of which are some of the largest electronics companies.The letters JEDEC stand for Joint Electron Device Engineering Council, and as the name indicates it manages and develops many standards associated with semiconductor devices of all types. One aspect of this is the surface mount technology component packages.
Obviously different SMT packages are used for different types of components, but the fact that there are standards enables activities such as printed circuit board design to be simplified as standard pad sizes and outlines can be prepared and used.
Additionally the use of standard size packages simplifies the manufacture because pick and place machines can use standard feed for the SMT components, considerably simplifying the manufacturing process and saving costs.
The different SMT packages can be categorised by the type of component, and there are standard packages for each.
Passive surface mount devices are mainly comprised of SMD resistors and SMD capacitors. There are several different standard sizes which have been reduced as technology has enabled smaller components to be manufactured and used
It will be seen that the devices size names are derived from their measurements in inches.
Small surface mount capacitors are used by the billion in all forms of mass produced electronic equipment. Surface mount capacitors are nomally small rectangular cuboids the dimesnions of which normally manufactured to conform to the industry standard sizes. SMCD capacitors may use a variety of technologies including multilayer ceramic, tantalum, electrolytic and some other less widely used varieties.
Surface mount technology offers significant advantages for the mass production of electronic equipment. Small surface mount resistors are used by the billion in all forms of mass produced electronic equipment. Resistors are typically very small cuboid devices and they are normally manufactured to conform to the industry standard sizes
Although the main use for these sizes surface mount component packages is for SMD resistors and SMD capacitors, they are also used for some other other components. In some cases it is not physically possible to adopt these standard sizes, but some other components do use them. One example is that is SMD inductors. Naturally it is very difficult for the very smallest sizes, but SMD inductors are available in 0805 and 0603 sizes.
As a result of the different construction and requirements for tantalum SMT capacitors, there are some different packages that are used for them. These conform to EIA specifications.
There are several types of other component that are not able to adopt the standard surface mount component sizes used by the majority of SMD resistors and capacitors.
Surface mount versions of components like many types of inductor, transformers, quartz crystal resonator, temperature controlled crystal oscillators TCXOs, filters, ceramic resonators and the like may require different style packages, often larger than the ones that are sued for surface mount resistors and capacitors.
These packages are unlikely to adopt the standard surface mount component package sizes in view of the unique nature of the components.
Whatever the package style chosen it must be able to fit the automated PCB assembly processes and be handled by a pick and place machine.
SMD package types describe the physical characteristics of devices that use surface mount technology (SMT) for attaching electronic components directly to the surfaces of printed circuit boards (PCB). In other words, an SMD is an electronic component that attaches to a PCB with SMT. This attachment method is faster than through hole technology (THT), which requires inserting component leads into drilled holes.
SMT supports the use of automated equipment and is a good choice for miniaturized components. Today, it is used widely with resistors, capacitors, transistors, diodes, and integrated circuits (ICs). Typically, SMD packages are named after their physical dimensions or have alphanumeric or lettered codes. The JEDEC Solid State Technology Association defines standards and some packages conform to EIA specifications.
The following sections describe common SMD package types and sizes.
SMD resistors and SMD capacitors have rectangular packages with numbered designations that represent inch-based measurements.
Contents
Surface-mount devices are mounted directly to a PCB. These components are smaller than the through-hole components and comprise a small lead or no lead at all. Since SMD components require fewer drilled holes, they incorporate higher routing density and the design becomes more compact.
There are many SMD components of different package sizes with various functionalities. They can be placed on both sides of the circuit board along with a higher component density with more connections possible per component to attain higher speed. Here, we will briefly introduce some of them.
An electronic project is incomplete without a proper connector. In surface-mount technology, SMA and SMB connectors are mostly used for board assembly. SMA and SMB stand for sub-miniature version A and sub-miniature version B.
TypePropertiesApplication SMA1. Semi-precision
2. Coaxial RF connector
3. Impedance 50Ω
4. Electrical use from DC (0 GHz) to 12 GHz,
but extended to 18 GHz and 26.5 GHz1. Microwave systems
2. Hand-held radio
3. Mobile telephone antennas
4. WiFi antenna systems SMB1. Semi-precision
2. Coaxial RF connector
3. Impedance 50Ω or 75Ω
4. Electrical use from DC(0 GHz) to 4 GHz
5. Smaller than SMA1.Telecommunications
2. Test equipment
3. Instrumentation
4. GPS
Tantalum capacitors do have very high capacitance with very small packaging. These capacitors give the best results in high-capacitance, low-current environments.
Package typeDimensions in mmEIA standard Size A3.2 x 1.6 x 1.6EIA 3216-18 Size B3.5 x 2.8 x 1.9EIA 3528-21 Size C6.0 x 3.2 x 2.2EIA 6032-28 Size D7.3 x 4.3 x 2.4EIA 7343-31 Size E7.3 x 4.3 x 4.1EIA 7343-43
A small outline transistor is a discrete surface-mount transistor that is majorly used in consumer electronics. Here are some commonly used SOTs.
Package typeDimensions in mmTerminal SOT-233 × 1.75 × 1.33 SOT-2236.7 × 3.7 × 1.84 SOT-3232.1 x 2.1 x 0.94 SOT-5231.6 x 1.6 x 0.74
We can see some popular SMD transistors other than SOT here.
TO-252-3 (DPAK)
TO-263
ICs are enclosed in a package for protection. Here we will see some important IC packages, their properties, and applications.
Package type
PropertiesApplication SOIC1. Small outline integrated circuit
2. Surface-mount equivalent of the classic through-hole DIP (Dual-Inline Package)1. Standard package for logic IC TSSOP1. Thin shrink small outline package
2. Rectangular surface mount
3. Plastic integrated circuit (IC) package
4. Gull-wing leads1. Analog amplifiers,
2. Controllers and Drivers
3. Logic devices
4. Memory devices
5. RF/Wireless
6. Disk drives QFP1. Quad flat package.
2. Easiest option for high pin-count components
3. Easy to inspect by AOI
4. Assembled with standard reflow soldering1. Microcontrollers
2. Multi-channel codecs QFN1. Quad flat no-lead
2. Electrical contacts do not come out of the component
3. Smaller than QFP
4. Require extra attention in PCB assembly1. Microcontrollers.
2. Multi-channel codecs PLCC1. Plastic leaded chip carrier
2. Allow components to be directly mounted on the PCB1. Prototype PCB assembly BGA1. Ball grid array
2. Most complex
3. High-pin count component
4. Electrical components are below silicon IC
5. Requires reflow soldering for PCB assembly1. High-speed microprocessor
2. Field programming gate array(FPGA) POP1. Package-on package technology
2. Stacked on the top of others1. Used for memory devices and microprocessors.
2. High-speed design, HDI design
SMD components ensure a smaller form factor design. The manufacturing cost is minimized and board space can be efficiently optimized by incorporating these components. Indeed, SMD packages are the better choice over through-hole components when designing a sleek, compact, high-speed, or HDI board.
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