The surface mount technology SMT is a popular mounting technique in PCB assembly. PCB assembly majorly focuses on component mounting. Surface mount devices are electronic components mounted directly on a bare PCB. In the PCB industry, the surface mount technology has replaced the through-hole technology.
Most modern electronic equipment comprise minute devices. Surface mount technology was specifically introduced to minimize production costs while making good use of PCB space. Therefore, the introduction of this technology has enabled the production of highly complex electronic circuits.
What is Surface Mount Technology?
The surface mount technology is a type of mounting technique in PCB assembly. It involves the mounting of electrical components directly on a PCB surface without any drilling. Also, these components feature no leads or smaller leads. Also, SMT components are smaller than through-hole components.
Surface mount electronic components are more suitable and compact for higher routing density since they don’t require drilled holes. Electronic devices that incorporate SMT are more beneficial. The surface mount technology process involves several steps. Also, this PCB assembly involves the use of automation. It uses pick and place machines to place electronic components on bare boards.
SMT involves the use of components that are compact in structure and high in safety density. Also, SMT involves the use of reflow soldering.
Steps Involved in SMT Process
There are several steps involved in the surface mount process. Each of these steps determines the success of surface mount technology. Therefore, it is crucial to pay attention to each of these steps.
Solder paste printing
This step involves the application of solder paste on a PCB surface. The PCB assembler uses stencil and squeegees to apply solder paste. Also, solder paste is a mixture of tin and flux. The solder paste helps to connect the SMT components and solder pads on the PCB. Solder paste printing prepares the electronic components for welding.
It is crucial that every pad has the right amount of paste. Otherwise, there won’t be any connection when melting the solder in the reflow process. Therefore, it is crucial to control the quality of the solder paste printing process.
Component placement
Once the PCB assembler has applied solder paste, the next step is components placement. Component placement involves mounting every component on the PCB. Here, the pick and place machine places the component in its programmed location. Also, the pick and place machine can place about 80,000 surface mount electronic components per hour.
Automated optical inspection
It is important to inspect all individual components after placing then on the PCB board. This helps to ensure these components are properly placed. Therefore, this step helps to detect any placement error and solder the parts into the right position.
Reflow soldering
After making all the necessary checks, the PCB assembler will move the PCB into a machine. The reflow soldering machine helps to create electrical solder connections between the PCB and components. Here, the PCB goes through a conveyor belt where it is heated. The assembler inspects the PCB again after it has gone through reflow soldering.
Different Types of SMD Components
There are different types of surface mount devices (SMDs). SMDs need to withstand high soldering temperatures. Therefore, you must carefully select, place, and solder them in order to achieve great manufacturing result. The two major types of surface mount electronic components are passive and active components.
Passive SMD components
The shapes of passive SMD components are cylindrical and rectangular.
- Surface mount resistor networks
These SMD components are widely used as replacement for discrete resistors. Therefore, this helps to save placement time. Generally, surface mount networks are available in 16 to 20 pins with about 2 watts power per package.
- Surface mount discrete resistors
Surface mount discrete resistors are available in two main types which are thin and thick film. Also, the construction of thick film resistors involves screening resistive film on a high purity alumina substrate surface. Thin film resistors have a resistive element on a ceramic laminate with protective coating solderable terminations. These terminations feature an adhesion layer on the ceramic substrate.
- Surface mount tantalum capacitors
The dielectric of surface mount capacitors can be tantalum or ceramic. Surface mount tantalum capacitors provide high capacitance-voltage product for each unit volume. Also, the wrap-under lead capacitors feature leads rather than terminations as a polarity indicator. When utilizing the molded plastic tantalum capacitors, there are no concerns for placement or soldering.
These capacitors are in two case sizes which are extended and standard range. Also, the capacitance value for these capacitors varies. Furthermore, these capacitors can be custom made based on the application’s requirement.
- Surface mount ceramic capacitors
Surface mount capacitors are suitable for high frequency applications since it doesn’t have leads. Also, 8mm tape and reel is the most commonly used packaging for ceramic capacitors. Surface mount ceramic capacitors are ideal for use in frequency control and decoupling capacitors. Furthermore, multilayer monolithic ceramic capacitors have enhanced volumetric efficiency.
Active SMD components
- Plastic leaded chip carriers (PLCC)
PLCC have leads that offer the compliance required to withstand the solder joint stress. Therefore, this prevents cracking in the solder joint. PLCC is a much cheaper version of ceramic chipcarrier. Also, PLCCs having large die-to-package ratios may be prone to package cracking as a result of moisture absorption. Therefore, they require proper handling.
- Fine pitch SMD packages
These are surface mount packages that feature large number of leads and very fine pitch. Also, fine pitch packages feature thinner leads and demand thinner land pattern designs.
- Leadless ceramic chip carriers (LCCC)
Leadless chip carriers feature no leads. Rather, they feature groove-shape terminations that offer shorter signal paths that enable higher operating frequencies. Leadless ceramic chip carriers are in different families based on the pitch of the package. The 50 mil family is the most common. However, they are other families like 20, 25, and 40 mils.
- Small outline Integrated Circuit (SOIC)
SOIC is a shrink package that features leads on 0.050 inch centers. Also, the small outline integrated circuit helps to house larger integrated circuits. SOIC comprises leads on two sides that are created outward. This is generally known as gul wing lead. Also, SOICs need careful handling to avoid any lead damage. SOICs are available in two different body widths which are 150 mils and 300 mils.
- Small outline J packages (SOJ)
The SOJ packages feature pins on only two sides. The small outline J package is a hybrid of PLCC and SOIC. Also, the SOJ packages combine the space efficiency of SOIC and handling benefits of PLCC. SOJ packages are widely used for high density DRAMSs.
What is the Difference Between SMT and SMD?
Surface mount technology (SMT) refers to the entire process of mounting and soldering electronic components directly on a PCB. SMD also known as surface mount device is the component mounted on the PCB surface. PCB assemblers soldered components by hand in the early stages. At that time, the pick and place machines could handle just a few simple components.
The introduction of surface mount components gave birth to a new era. While surface mount technology is a process of PCB assembly, a surface mount device is an actual component. People usually confuse SMT and SMD. Both surface mount devices and surface mount technology are intertwined. Both SMT and SMD work hand in hand to obtain reliable and functional PCBs.
Surface mounting helps to eliminate the need to pass leads through a printed circuit board. Also, surface mounting saves spaces and allows the installation of more components on a smaller circuit board. Surface mount technology is responsible for the production of smaller electronic devices.
The production of a functional electrical device requires the selection of SMDs and the adoption of SMT. This is why SMT and SMD overlap. Surface mount devices like integrated circuits are components mounted on a printed circuit board. The more recent SMDs now utilize pins you can solder directly onto circuit boards. With SMDs, PCB assemblers can fit more components on a smaller printed circuit board.
Proper selection of SMDs is crucial for SMT. Therefore; SMT is a strategy for working effectively with SMDs. SMT machines can mount thousands of SMDs on circuit boards within a short time. Also, the type of SMDs used for the PCB production process will determine the effectiveness of the entire SMT assembly process.
Difference Between Surface Mount Technology and Through Hole Technology
Surface mount technology and through hole technology are the two major techniques in PCB assembly process. These two technologies are commonly used in installing electronic components on PCB surface. However, the technique and the processes of these technologies differ.
Through hole mounting involves the process of placing component leads into drilled holes on a PCB board. This mounting process was initially introduced before the advent of surface mount technology. Also, through-hole technology involves the use of through-hole components. However, SMT uses surface mount components. These components are well-secured by the solder on the PCB surface.
SMT involves mounting components directly on the surface of a circuit board. Most electronic devices use SMT. One of the major differences between SMT and THT is that SMT doesn’t need the drilling of holes through a circuit board. Also, surface mount electronic components are much smaller than THT components.
Furthermore, SMT uses reflow soldering while THT uses wave soldering. SMT helps to produce more complex and compact devices since it allows the placement of thousands of components on a PCB. Also, SMT has more pin count than through-hole technology.
SMT offers higher packing density than through-hole mounting since SMT components are more compact. Also, SMT components are less expensive than through-hole components. While SMT adopts assembly automation, THT adopts manual assembly. Therefore, SMT is more ideal for high volume productions.
The capital needed for investing in machinery for SMT is higher that of THT. Furthermore, the process and technology demanded by SMT is more advanced than that of THT. Through-hole technology is ideal for bulky and large components subjected to high and frequent mechanical stress.
Advantages and Disadvantages of Surface Mount Technology
Surface mount technology offers a lot of benefits and disadvantages.
Advantages
- Reduced board size
SMT helps to save more space when used in PCB manufacturing. Also, this technology ensures the placement of more components on a PCB. With SMT, PCB manufacturers can now design compact and complex boards. These boards are then used for the production of advanced electronic devices.
- High frequency and signal transmission
SMT supports high density on multilayer boards. Also, SMD components feature short leads or no lead. Therefore, it reduces RF interference. In addition, SMT offers more resistance to vibration.
- Automated production
The use of automation makes SMT assembly process easier. Also, the pick and place machine makes component placement easier.
- Reduced material cost
SMT doesn’t require drilling of holes. Drilling holes on a circuit board is a time consuming and costly effort. Also, SMD components are less expensive than through hole components. Therefore, all these help to reduce the cost of manufacturing. Also, there is reduced cost as regards handling and packaging since surface mount assemblies are smaller.
- PCB flexibility
Surface mount technology provides more flexibility as regards PCB design and material. Also, surface mount electronic components are directly soldered on the PCB surface. Therefore, this offers great flexibility for PCB boards.
Disadvantages
- Difficult to inspect
SMD components are very small and have several solder joints. Therefore, this can make PCB inspection difficult. BGA packages have solder joint problems that can be difficult to inspect. Several solder joint types make inspection difficult to perform.
- High cost
SMT is a very costly process. Also, it requires large investment in equipment and high training costs. Most SMT equipment are very expensive. In addition, these pieces of equipment need to be handled by a professional due to their technical complexity.
- Prone to damage
SMD components are prone to damage when they drop. Therefore, these components need proper care when handling and packaging them.
Conclusion
SMT is a commonly used assembly technique in the PCB industry. Also,this mounting technology is widely used in applications like automotive and communications electronics. SMDs play a crucial role in surface mount technology. Surface mount technology has contributed to the development in the electronics industry.
