With the global demand for more heat-tolerant and lightweight
electronics such as laptops and smartphones, small and large-scale
manufacturers have continued to rely on SMT assembly to mass produce such
products. The market size for this technology has been predicted to increase by
more than 8.1% from 2023 to 2032.
Then, what is SMT
assembly? How does it differ from traditional assembly methods? In this blog,
we will explain in detail what SMT is, the SMT process, and the advantages of
using SMT PCB assembly.
What Is SMT: The Basics
SMT stands for surface mount technology. It is a technique of
joining smaller electronic components.
SMT assembly means assembling SMD components, such as diodes, resistors, and capacitors, onto a
laminate substrate (PCB). This design allows for compact placement of
components, enabling efficient use of PCB space.
The role of SMT assembly in the current industry is enormous. For
example, It decreases the device sizes by more than 50%. In addition, it
enhances the heat dissipation and reduces the power consumption of the devices.
What is SMD?
SMD stands for surface mount devices. They are the components that
are mounted or attached to a PCB. They have short terminals which grip them
very firmly to the plane of the circuit board. Some examples are capacitors,
LEDs, transistors, and resistors.
Key SMT Assembly Process
There are six main steps to follow when carrying out SMT assembling
of components. They are:
a. Layout and Design
Layout design consists of finding a usable space on the board on
which the SMDs can fit themselves. In order to guarantee that each component
bonds correctly, calculations are made to determine a fixed board size, shape,
and thickness. Afterward, technicians decide on the optimal positions and
orientations with the components.
b. PCB
Fabrication
The fabrication starts with selecting suitable epoxy-based silica
materials like the FR4 and FR5. After that, the printed board layer is
fabricated. Next, the copper foil layer is created using etching and laminating
techniques, followed by the silkscreen layer, which is applied using silkscreen
printing and ink curing.
After the layers align properly, molten copper is deposited on the
previously designed layout on the PCB, and excess copper is removed along the
board paths.
c.
Stencil Design & Manufacturing
Materials selection is incorporated in this procedure, for
example, deciding the best materials, such as stainless steel, for the
rendering. After that, the stencil is created using laser cutting or chemical
etching.
d.
Solder Paste Application
This includes pre-heating the solder to a paste prior to its
top-coating on the PCB at a temperature ranging from 220 to 250 °C.
Subsequently, the paste is stamped onto the PCB through a stencil. At the end
of the process, the board and paste are allowed to sit at room temperature.
e.
Component Placement
It focuses on the application of pick and place machines to attach
the circuit modules to the board. Before putting the pieces in the right place
they are sorted in reels or trays. Following this, the machine lifts each part
and drops them into the correct position.
Then, the operator performs a visual check to ensure all
components are correctly positioned.
f.
Testing and Inspection
This is done to check the integrity of the assembled elements. For
this, operators employ either Automated X-ray Inspection (AXI) or Automated
Optical Inspection (AOI) machines to check the soldered joints.
Designers conduct this test to detect defects such as solder
bridges or incorrect positioning of the circuit devices.
g.
Cleaning
Such an approach is taken to detoxify the PCB by exploiting
surface-cleaning techniques such as ultrasonic cleaning or cleaning with a
solvent. Isopropanol or deionized water is employed to wipe the board surfaces
for this purpose.
SMT
Assembly
Advantages
In industry, manufacturers are generally keen to apply this
technology for the mass production of components because of the many advantages
that it provides. A few of these merits are discussed below.
a. It Has Good Thermal Efficiency
SMT assembly enables better thermal management because it reduces
the size of the SMDs attached to the circuit board. The assembling lines have
thermal pads, vias, and other heat reduction techniques to balance the heat
dissipation in the system.
b. Cost Effectiveness
SMT technology lowers labor costs through automated production
units that reduce product quality problems caused by human mistakes.
c. It Supports Complex PCB Designs
Thanks to the SMT assembly, it is feasible to place intricate
patterns of devices over the board as the components can be positioned into a
more compact area of the board.
d. It Offers Higher Durability and
Reliability
Due to the high adhesion of the mounted devices on the surface of
the PCB, which prevents damage caused by shock, thermal, and mechanical stress,
the SMT attaching process makes highly durable PCBs possible.
e. Lower Space Requirements
Surface-mount techniques take up less room than conventional
through-hole technology. The main reason is the reduction in the size of
Surface Mount Devices (SMDs) that can be directly attached to PCB without any
holes.
Disadvantages of SMT Assembly
Although used daily within the electronics industry, SMT
technology is still associated with problems/difficulties, making the process
undesirable for small-scale manufacturers. Some of these challenges include:
a. It is Difficult and Costly to
Repair
It is hard to repair most SMT circuits because of the compact
mounting of components. Because of the high packing density, there is very
limited space for technicians to work on the replacement of faulty components.
Due to this, repair work becomes time-consuming and expensive.
b. Requires High Initial Investment
Initial equipment cost and training of staff are both very high
when setting up an SMT production line. Due to this high capital intensity, the
technology is less appealing for small businesses operating on limited budgets.
c. Complexity In Testing
The smaller electronic components used in SMT are increasing the
challenges for technicians carrying out visual inspection, compared to
traditional through-hole technology.
d. It is Highly Sensitive to Heat
Several SMT devices are susceptible to thermal effects during
their fabrication, which in turn results in a shorter lifespan.
e. It makes the Solder-Paste
Application difficult
The presence of solder in the SMT fabrication process creates
various problems, including inadequate wetting, oxidation, and misalignment of
components. These defects can result in electrical connectivity issues that
degrade the integrity of the final product.
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Conclusion
The advantages of SMT assembly, such as space-saving and good
operational performance, cannot be ignored despite the problems it raises. In
particular, the high cost of repairs makes the system very expensive for small
companies. In spite of this, SMT is still the preferred choice for electronics
manufacturing, even with the scaling up of manufacturing energy-saving devices.
For students, engineers, or manufacturers in training, knowing
both the benefits and drawbacks of SMT is critical to effectively utilize the
technology.
