Surface mount technology is a part of the electronic assembly that deals with the mounting of electronic components to the surface of a PCB. Electronic components mounted this way are called surface-mounted devices (SMD).
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SMT was developed to minimize manufacturing costs while making efficient use of board space. The introduction of surface mount technology has enabled manufacturers to fabricate smaller size complex circuit boards. There are various advantages and disadvantages of surface mount technology which we will discuss over the course of this article.
Surface-mount technology was developed in the s and was broadly used in the s. By the s, they were used in most of the high-end PCB assemblies. Conventional electronic components were redesigned to include metal tabs or end caps that could be attached directly to the board surface. This replaced typical wire leads which needed to pass through drilled holes. SMT led to much smaller components and enabled component placement on both sides of the board. Surface mounting enables a higher degree of automation minimizing labor costs and expanding production rates that results in the development advanced of boards.
SMT allows electrical components to be mounted on the board surface without any drilling. Most electronic applications prefer to use surface mount components since they are compact and may be installed on either side of a printed circuit. They are suitable for applications with higher routing densities. These components have smaller leads or no leads at all and are smaller than through-hole components.
The process involved in SMT assembly is:
In through-hole technology, the component leads are inserted into the drilled holes on the board. These leads are then soldered to pads on the opposite side using wave soldering or re-flow soldering tools. Since through-hole mounting offers strong mechanical bonds, it is highly reliable. However, drilling PCBs during production tends to increase manufacturing costs. Also, through-hole technology limits the routing area for signal traces below the top layer of multi-layer PCBs.
SMT has many advantages over conventional through-hole technology:
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Even though SMT has several advantages, the technology also comes with it certain disadvantages:
The majority of products manufactured at this time utilize surface mount technology. But SMT is not suitable in all cases. Consider SMT considered if:
Here are some recommendations for SMD placement to maintain good signal and power integrity for your board.
To facilitate the assembly process ensure that all component names, polarities, orientations, and placements are marked properly in the assembly drawing. The footprints present in the drawings should match with the actual parts. Consult your manufacturer for their kitting guideline if you are considering consigned assembly. Prepare your BOM accordingly.
Solder reflow and wave soldering are widely used to mount components onto the board. Depending on the nature of the components, the designer can choose one of these methods for surface mounting technology.
Wave soldering: Since the solder will flow through the holes to form a connection, wave soldering is mostly used for through-hole components. You can use wave soldering for most of the surface-mount components also.
Solder reflow: This process is generally preferred in SMT. Here, the solder on one pin melts and reflows faster than the other. The only disadvantage is that it causes a tombstoning effect, where the component peels away from the non-melted pad. This effect is common for surface mount components like resistors, capacitors, and inductors.
SMD packages come in a broad range of shapes and sizes as given below:
Common passive discrete components: These components are mostly resistors and capacitors and are a part of most electronic devices available today. Given below are SMD package details for capacitors and resistors.
Transistors: The common type of packages for transistors are as follows:
Integrated Circuit (IC) packages
Integrated Circuit packages come in a wide range as given below:
Small Outline Package (SOP)
TSOP (Thin Small Outline Package) is thinner than SOIC
Quad flat packs are generic square, flat IC packages.
BGA packages include an arrangement of solder balls on the chip underside in the place of pins. The ball spacing typically is 1.27, 0.8, 0.5, 0.4, and 0.35mm
The chip is enclosed in a plastic mold. It can either be square or rectangular in shape.
Surface mount component standards are specified by the Joint Electron Device Engineering Council (JEDEC) Solid State Technology Association (JEDEC.org). JEDEC is an independent semiconductor engineering trade organization and standardization body that has its headquarters in Arlington, Virginia, United States.
You can measure SMD size in inches in the Imperial system and millimeters in the Metric system. For the imperial components, the dimensions are 0.02 x 0.01 inches. For the metric components 0.2 x 0.1 mm.
Understanding the advantages and disadvantages of surface mount technology is essential to comprehend its role in the electronics industry. This will always help in optimizing your design and assembly skills. Follow the guidelines listed in this article to completely benefit from the SMT process for component placement. Please comment below if you have any queries on employing surface mount technology for your design. We will be happy to help you.
Surface mount technology is a part of the electronic assembly that deals with the mounting of electronic components to the surface of a PCB. Electronic components mounted this way are called surface-mounted devices (SMD).
SMT was developed to minimize manufacturing costs while making efficient use of board space. The advent of surface mount technology has empowered manufacturers to create intricate circuit boards in smaller sizes. Throughout this article, we'll explore the numerous pros and cons associated with surface mount technology.
Surface mount technology emerged in the s and gained widespread usage in the s, becoming prevalent in most high-end PCB assemblies by the s. It involved redesigning conventional electronic components to incorporate metal tabs or end caps that could be directly attached to the board's surface, eliminating the need for wire leads to pass through drilled holes. This shift to SMT resulted in significantly smaller components and allowed for component placement on both sides of the board. The introduction of surface mounting facilitated increased automation, reducing labor costs, and expanding production rates, thereby advancing the development of circuit boards.
Surface mount technology (SMT) allows electrical components to be affixed to the board surface without requiring drilling. Most electronic applications favor surface mount components due to their compact size and the ability to install them on either side of a printed circuit. They are particularly suitable for applications with high routing densities, featuring smaller leads or no leads at all compared to through-hole components.
1. Applying solder paste to the fabricated circuit board using stencils. Solder paste comprises flux and tin particles.
2. Attaching the surface mount components.
3. Employing a reflow method for soldering.
In through-hole technology, component leads are inserted into drilled holes on the board. Subsequently, these leads are soldered to pads on the opposite side using wave soldering or reflow soldering tools. This method provides strong mechanical bonds, ensuring high reliability. However, the process of drilling PCBs during production tends to elevate manufacturing costs. Additionally, through-hole technology constrains the routing area for signal traces, particularly below the top layer of multi-layer PCBs.
1. SMT eliminates the constraints on board space imposed by through-hole mounting during the manufacturing process.
2. Through-hole components typically incur higher manufacturing costs compared to SMT components.
3. Utilizing SMT demands advanced design and production skills compared to through-hole technology.
4. SMT components can accommodate a higher pin count in comparison to through-hole components.
5. Unlike through-hole technology, SMT allows for assembly automation, making it suitable for high-volume production at lower costs compared to through-hole production.
6. SMT components offer higher component density due to their compactness compared to through-hole mounting.
7. Although surface mount technology reduces production costs, the machinery's capital investment required is higher than that for through-hole technology.
8. Through-hole mounting is more suitable for manufacturing large and bulky components that experience occasional mechanical stresses or for high-voltage and high-power parts.
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9. SMT facilitates achieving higher circuit speeds due to its reduced size and fewer holes.
1. Component stability under external stress exposure
2. Thermal management and heat dissipation ease
3. Part availability and alternatives
4. Cost-effectiveness in assembly
5. High performance and package lifespan
6. Rework feasibility in case of board failure
1. SMT supports microelectronics by enabling closer placement of components on the board, resulting in more lightweight and compact designs.
2. The production setup process for SMT is faster than through-hole technology as components are mounted using solder paste instead of drilled holes, saving time and reducing labor-intensive work.
3. Components can be placed on both sides of the circuit board, allowing for higher component density and more connections per component.
4. Due to the compact package size, higher-density traces can be accommodated on the same layer.
5. Molten solder's surface tension aligns components with solder pads, automatically correcting minor placement issues.
6. Unlike through holes, SMT components do not expand during operation, enabling reduced inter-packaging space.
7. SMT boards achieve electromagnetic compatibility easily due to their compact package and lower lead inductance.
8. Lower resistance and inductance at connections in SMT mitigate undesired effects of RF signals, providing better high-frequency performance.
9. Compactness allows more parts to fit on the board, resulting in shorter signal paths and enhanced signal integrity.
10. SMT components dissipate less heat compared to through-hole components.
11. SMT reduces board and material handling costs.
12. Enables a controlled manufacturing process, particularly beneficial for high-volume PCB production.
1. Reliability concerns arise when relying solely on surface mounting for components exposed to mechanical stress, as component connectors are required for interfacing with external devices that are periodically removed and reattached.
2. Solder connections for surface-mounted devices (SMDs) may sustain damage due to thermal cycles during operations.
3. Skilled operators and expensive tools are necessary for component-level repair and manual prototype assembly due to smaller sizes and lead spaces.
4. Most SMT component packages cannot be installed in sockets, hindering easy installation and replacement of failed components.
5. The reduced solder used in SMT raises reliability concerns for solder joints, with void formation potentially leading to solder joint failures.
6. SMDs are typically smaller than through-hole components, providing limited surface area for marking part IDs and component values, complicating identification during prototyping and PCB repair.
7. Solder in SMT can melt under intense heat, limiting its use in electrical load circuits with high heat dissipation.
8. Implementation of SMT in PCBs requires higher installation costs due to the expensive equipment involved, such as hot air rework stations, pick and place machines, solder paste screen printers, and reflow ovens.
9. Miniaturization and various solder joints can make procedures and inspections more challenging.
10. The compact size increases the risk of solder overflow, leading to short circuits and solder bridges.
While the majority of current products are manufactured using surface mount technology, it's important to note that SMT might not be suitable for all cases. Consider using SMT if:
1. High component density needs to be accommodated.
2. The product requires a compact or small form factor.
3. The final product needs to be sleek and lightweight while maintaining high component density.
4. High-speed or high-frequency functionality is required.
5. Large quantities need to be produced using automated technology.
6. The product should generate minimal or no noise.
1. Position components as close as possible to minimize routing distance.
2. Follow the schematic's signal path when placing components.
3. Avoid placing components in the return path of sensitive signals to prevent signal integrity issues.
4. For high-speed devices, position bypass capacitors nearer to their power pins to minimize parasitic inductance.
5. Group SMDs together for power supply circuits to enable shorter routing and reduce connection inductance.
6. Consider placing SMT components on one side of the board to reduce costs related to stencils and assembly.
7. Adhere to the manufacturer's specifications for minimal spacing between test points and SMT components, which may vary based on component height.
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