Advantages and Disadvantages of SMT

Contents

For more information, please visit Smt Vs Smd LED.

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 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.

The advent of surface mount technology

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.

Salient features of SMT and through-hole technology

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:

• Apply solder paste to the fabricated circuit board using stencils. Solder paste is made up of flux and tin particles.
• Attach the surface mount components.
• Use a reflow method for soldering.

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.

Major differences between through-hole technology and surface mount technology

• SMT frees up the limitation on board space posed by the through-hole mounting manufacturing process.
• Through-hole components involve higher manufacturing costs than SMT components.
• You require advanced design and production skills for using SMT when compared to through-hole technology.
• SMT components can have a higher pin count as compared to through-hole components.
• Unlike through-hole technology, SMT enables assembly automation which is suitable for high production volumes at lower costs when compared to through-hole production.

• SMT components are more compact leading to higher component density as compared to through-hole mounting.
• While surface mount leads to lower production costs, capital investment for machinery is higher than needed for through-hole technology.
• Through-hole mounting is better suited to the production of large and bulky components that are subjected to periodic mechanical stresses or even high-voltage and high-power parts.
• SMT makes it easier to achieve higher circuit speeds because of its reduced size and fewer holes.

Factors to consider before choosing SMT or through-hole technology

• Stability of the component when exposed to external stress
• Ease of thermal management/ heat dissipation
• Availability of the part and its alternative
• Cost-effectiveness of assembly
• High performance and life-span of the package
• Facilitate rework in case of board failure

Advantages of surface mount technology

SMT has many advantages over conventional through-hole technology:

• Surface mount technology supports microelectronics by allowing more components to be placed closer together on the board. This leads to designs that are more lightweight and compact.
• The process for SMT production setup is faster when compared to through-hole technology. This is because components are mounted using solder paste instead of drilled holes. It saves time and labor-intensive work.

• Components can be placed on both sides of the circuit board along with a higher component density with more connections possible per component.
• Due to the compact size of the package, higher-density traces can be accommodated on the same layer.
• The surface tension of molten solder pulls components into alignment with solder pads, which automatically corrects minor placement problems.
• Compared to through holes, these do not expand in size during the operation. Hence you can reduce the inter-packaging space.
• Electromagnetic compatibility is easily achievable in SMT boards because of their compact package and lower lead inductance.
• SMT enables lower resistance and inductance at the connection. It mitigates the undesired effects of RF signals and provides better high-frequency performance.
• More parts can fit on the board easily due to their compactness, resulting in shorter signal paths. This enhances signal integrity.
• The heat dissipated is also lesser than through-hole components.
• SMT reduces board and material handling costs.
• Enables you to have a controlled manufacturing process. This especially opted for high-volume PCB production.

Ensure the manufacturability of your circuit design using the Better DFM tool.

 

Disadvantages of surface mount technology

Even though SMT has several advantages, the technology also comes with it certain disadvantages:

• When you subject components to mechanical stress, it is not reliable to use surface mounting as the sole method of attachment to the PCB. This is because you need to use component connectors to interface with external devices that are periodically removed and re-attached.
• Solder connections for SMDs might be damaged through thermal cycles during operations.
• You would need highly skilled or expert-level operators and expensive tools for component-level repair and manual prototype assembly. This is because of the smaller sizes and lead spaces.
• Most SMT component packages can&#;t be installed in sockets that enable easy installation and replacement of failed components.
• You use less solder for solder joints in SMT, therefore the reliability of solder joints becomes a concern. Void formation might lead to solder joint failures here.
• SMDs are typically smaller than through-hole components leaving lesser surface area for marking part IDs and component values. This makes identifying components a challenge during prototyping and repairing the PCB.
• The solder can melt when exposed to intense heat. Therefore, SMT cannot be implemented in electrical load circuits with high heat dissipation.
• PCBs that use this technology requires more installation costs. This is because most of the SMT equipment such as the hot air rework station, pick and place machine, solder paste screen printer, and reflow oven are expensive.

• Miniaturization and a variety of solder joints can make the procedure and inspection more difficult.
• Due to compact size, there is an increased chance of solder overflow that can result in short circuits and solder bridge.

 

Design for Testing Handbook

7 Chapters - 28 Pages - 45 Minute Read

What's Inside:

• PCB testing strategies
• Guidelines to design and place a test point for FPT
• Directives to make your board ICT compatible
• Benefits and drawbacks of various testing methods
• Defects that you can identify through board testing

Download Now

 

When to use surface mount technology?

The majority of products manufactured at this time utilize surface mount technology. But SMT is not suitable in all cases. Consider SMT considered if:

• You need to accommodate a high density of components.
• The need is for a compact or small product.
• Your final product needs to be sleek and light despite component density.
• The requirement specifies the high-speed/frequency functioning of the device.
• You need to produce large quantities with automated technology.
• Your product should produce very little noise (if any at all).

Guidelines for SMT component placement

Here are some recommendations for SMD placement to maintain good signal and power integrity for your board.

• Keep the components as near as possible to minimize the routing distance.
• Adhere to the signal path as per the schematic while placing the components.
• Never place the components in the return path of sensitive signals. This leads to signal integrity issues.
• For high-speed devices, place the bypass capacitors closer to their power pins. This will reduce parasitic inductance.
• Arrange the SMD together for power supply circuits. This will help you to provide shorter routing and reduce the inductance in the connections.
• Try to keep SMT components on one side of the board to reduce costs associated with stencils and assembly.
• Maintain the minimal spacing between the test points and SMT components as specified by your manufacturer. This spacing may vary depending on the component&#;s height.

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.

 

 

Soldering techniques employed in SMT

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.

Surface mount device packages

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:

• SOT-23 (Small Outline Transistor) with dimensions 3 x 1.75 x 1.3mm
• SOT-223 (Small Outline Transistor) with dimensions 6.7 x 3.7 x 1.8Mmm

Integrated Circuit (IC) packages

Integrated Circuit packages come in a wide range as given below:

• Small Outline Integrated Circuit (SOIC)

Small Outline Package (SOP)

TSOP (Thin Small Outline Package)  is thinner than SOIC

• Quad Flat Pack (QFP)

Quad flat packs are generic square, flat IC packages.

• Ball Grid Array (BGA)

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

• Plastic Leaded Chip Carrier

The chip is enclosed in a plastic mold. It can either be square or rectangular in shape.

Measurement of SMD size

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.

 

Design for Assembly Handbook

6 Chapters - 50 Pages - 70 Minute Read

What's Inside:

• Recommended layout for components
• Common PCB assembly defects
• Factors that impact the cost of the PCB assembly, including:
  • Component packages
  • Board assembly volumes

Download Now

When you plan a PCB assembly project, SMD, SMT, and PTH are three terms you can't miss. The following is what this article reveals:

Part 1: What is SMD

SMD stands for the surface-mounted device. SMDs are electronic components that are picked and placed on PCBs during the SMT assembly, and there are passive SMDs and active SMDs.

Passive SMDs: electronic components that do not consume or convert electric energy, such as resistors, capacitors, inductors, wave filters, couplers, and antennas. Passive SMDs do not change the signal features but only let them pass. And they work only if there comes signal input, with no need for an external power supply.

Active SMDs: electronic components that consume and convert electric energy, such as ICs, transistors, silicon-controlled rectifiers, diodes, triodes, and valves. Active SMDs generate signals in analog and digital circuits and can change signal features. And they work with signal input and external power supply.

SMDs have very short pins, and their sizes are about only 1/10 of the through-hole components. Packaging sizes of SMDs include , , , , , , , , .

SMD vs SMT

SMT is a PCB assembly technology, while SMDs are PCB parts mounted via SMT technology.

Please see details about SMT below.

Part 2: What is SMT

SMT stands for surface-mounted technology. SMT is the main technology for PCB assembly, and it is automatic. SMT assembly can meet fine-pitch requirements, while the other technology PTH can't be fine-pitch.

Currently, almost all electronic components can be surface mounted, especially for high-dense circuits. As electronic products are smaller and smaller, SMT is the trend of PCB assembly.

The steps of SMT assembly are:

Step 1. PCB manufacturing and SMT stencil manufacturing

Step 2. Solder paste printing on PCB pads via SMT stencils

Step 3. Solder paste inspection to check solder paste thickness and shapes

Step 4. High-speed SMT assembly (high-speed SMT machine picks and places SMDs of and below)

Step 5. Function SMT assembly (functional SMT machine picks and places SMDs of and above)

Step 6. (optional) X-ray test if there are BGAs (ball grid array, a surface-mounted packaging) on the PCBA

Step 7. Reflow soldering to melt and cure solder paste

Step 8. AOI test (automatic optical inspection) to make sure the SMDs are soldered correctly on the surface

For batch PCB assembly, the PCBA manufacturer PCBONLINE picks one of the first five PCB assembly pieces to go through the first article inspection (FAI). Then an FAI report is generated and sent to customers for review. Only when customers approve it, the batch PCB assembly start.

Are SMT assembly steps the same in all PCB assembly factories?

Yes.

Then why do we bother to compare different PCB assembly service providers at SMT manufacturing levels?

Because they have different SMT assembly capacities.

And the comparison in SMT manufacturing is necessary.

The main considerations for choosing SMT assembly companies are below:

• Lead-free assembly capability of reflow soldering ovens

RoHS standards require the PCB assembly to be lead-free. The lead-free reflow soldering temperature range is 240°C - 270°C, while the tin-lead reflow soldering temperature range is 210°C to 245°C.

• Fine pitch assembly

Pitch is the center-to-center distance between adjacent PCB pads, balls, or IC pins. Before you place your order, you need to ask the PCB assembly company for the smallest fine-pitch it can deal with.

Are you interested in learning more about Factory Wholesale Box Turning Conveyor Belt Equipment? Contact us today to secure an expert consultation!

• PCBA tests and conformal coating

You never want to spend extra time looking for test companies before your products enter the market. That's why you'd better work with a one-stop assembly company that completes all tests for your products.

And if you want the circuit boards to have a longer life span, find a PCB assembly company that can apply the conformal coating.

One-Stop Lead-Free Fine-Pitch SMT Assembly Services Provider | PCBONLINE

PCBONLINE is a leading one-stop PCB assembly services provider with customers around the world. It has competitiveness in contract electronic manufacturing for these advantages:

• 0.35mm fine-pitch SMT assembly capability with smallest SMD packaging
• Lead-free PCB assembly and the whole electronic manufacturing process RoHS certified
• PCB assembly following IPC-A-610 Class 2/3standards
• Complete PCBA tests such as thermal aging, functional testing, four-terminal sensing
• IC programming, conformal coating, and end-product assembly are available
• Fair PCB assembly prices. The more quantity, the lower PCBA per price

Please feel free to get a quote for your PCBA project online or by at . It is fast and free.

Part 3. What is PTH

PTH stands for through-hole assembly. PTH is a PCB assembly technology used less than SMT, done by component pins plug-in pre-set holes.

Through-hole PCB assembly has stronger mechanical stability than SMT soldering, but it can't meet the fine-pitch requirements.

PTH components are usually for plug needs, such as USB, type-C, and connectors. Capacitors of large capacitance can't be surface mounted, and they are usually also PTH components.

The PTH components area on the circuit board is much larger than SMDs'. Through-hole components have long pins so that they can plug into the pre-drilled holes on the PCB.

Here is the PTH assembly process:

Step 1. Let through-hole component pins through-hole manually

Step 2. Wave soldering to let tin fill the gaps between PTH component pins and through-hole walls

Step 3. Trim PTH component pins to be within 2mm

Step 4. Clean the extra flux on the PCBA surface

Step 5. (optional) IC programming, functional testing, thermal aging, end-product assembly

Part 4: SMT vs PTH, SMD vs PTH Components

In PCB assembly factories, both SMT lines and PTH lines are necessary. We can't say which is better because SMT and PTH serve different purposes. But you can see the differences between SMT and PTH from the comparison table.

SMT

THT or PTH

Necessity for PCB assembly

Necessary

Unnecessary if PCB has no plug needs

Method

Automatic

Usually manual

Complexity

Advanced

Simple

Density

High

Low

Soldering

Reflow soldering

Wave soldering

Speed

Fast

Slower than SMT

Precedence

Before PTH

After SMT

Through holes

No

Yes

Applications

Batch PCB assembly, high-density products

Prototype assembly, simple circuit boards

SMDs and through-hole components are only different in size and packaging.

PCB Components

SMDs

PTH components

Area on PCB

Small

Large

Weight

Light

Heavier than SMDs

Pins

Very short

Long

Fine-pitch

Can be fine-pitch

No

Prices

Normal

Lower than SMDs

Typical devices

Resistors, capacitors, inductors, ICs

Components for plug needs such as USB

At the one-stop PCB assembly factory of PCBONLINE, both SMT assembly and PTH assembly are available. If you order PCB assembly services from us, we can complete PCBA the next day (IPC-A-610 Class 2/3 standards) (at the fastest). The shipping usually takes 2 to 3 days.

Conclusion

This article gives an introduction to SMD, SMT, and PTH one by one, and it reveals the differences between SMT, SMD, and PTH components.

We can conclude that SMT is the mainstream PCB assembly technology, and PTH is mainly used when there are plug needs. SMDs and PTH components are mainly different in size and packaging. If you are looking for PCB assembly services, do not miss the 22-year-old turnkey PCBA source factory PCBONLINE.

Contact us to discuss your requirements of Automated Guided Vehicle Components. Our experienced sales team can help you identify the options that best suit your needs.