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Surface Mount Technology (SMT) is practice of soldering or mounting surface mount devices (SMD) on the surface of a printed circuit board (PCB). The principle behind surface mount technology is different from the conventional soldering process to solder thru-hole electronic components.
This comparatively new technology uses different different soldering principles and equipments. Also the process is little more complex than thru-hole technology but offers better reliability and electrical conductivity.
What is Surface Mount Technology?
Surface Mount Technology is a soldering technology where surface mount electronic components, also known as surface mount devices (SMD) are mounted or soldered on the surface of the printed circuit board. This technology uses solder paste in place or solder wire that is used in thru-hole soldering process.
SMT is mostly done using surface mount soldering equipment even though hand soldering is also done occasionally. Most manufacturing units using surface mount technology are cleanroom because most SMD electronic components, like semiconductors, are very sensitive to static charge. The cleanroom environment prevents these components from getting damaged.
Benefits of Surface Mount Technology
Surface mount technology offers benefits in terms of design and manufacturing. Design-related benefits include savings in weight and real estate and electrical noise reduction. SMT also provides improved shock and vibration resistance as a result of the lower mass of components. Manufacturing benefits of SMT include reduced board cost, reduced material handling cost, and a controlled manufacturing process.
What is SMD?
SMD stands for Surface Mount Device. These are electronic components with no leads like thru-hole components. These devices have tiny metallic legs very close to the surface of the components. These metallic legs are soldered on the copper tracing on the PCB using solder paste. BGA or Ball Grid Array is also a kind of SMD with no leads or legs at all. These special electronic components have tiny metallic spots underneath the components. They are soldered on the PCB using solder balls.
Most common SMD electronic components are:
SMD Passive Surface Mount Electronic Components for SMT -
- Surface Mount Discrete Resistors
- Surface Mount Resistor Networks
- Ceramic Capacitors for SMT
- Surface Mount Tantalum Capacitors
- Tubular Passive Components for SMT
SMD Active Surface Mount Electronic Components for SMT
- Leadless Ceramic Chip Carriers (LCCC)
- Small Outline Transistors (SOT)
- Small Outline Integrated Circuit (SOIC and SOP)
- Plastic Leaded Chip Carriers (PLCC)
- Small Outline J Packages (SOJ)
- Fine Pitch SMD Packages (QFP, SQFP)
- Ball Grid Array (BGA)
Surface Mount Technology Equipment
Surface mount equipment are different from equipment used in thru-hole soldering. There can be a number of SMT equipment but the most common of them are:
- SMT Solder Paste Screen Printer: A solder paste screen printer for SMT is needed to screen solder paste onto the printed circuit board (PCB) before placement of surface mount components.
- SMT Pick-and-Place Machine: A pick-and-place machine picks and places SMD electronic components onto the PCB prior to soldering.
- SMT Reflow Soldering Equipment: A reflow soldering equipment / machine is the second major equipment after pick-and-place machine in any SMT line.
- SMT Curing / Baking Oven: An oven is required for both adhesive curing and solder paste baking operations. The same or different ovens may be used for adhesive curing and baking of solder paste.
- SMT Solvent Cleaning Equipment: After soldering, the electronic assemblies must be cleaned to remove the flux and flux residues. The selection of solvent and cleaning equipment depends of the flux used and the cleanliness requirements.
- SMT Repair and Inspection Equipment: There are two main types of automated inspection equipment on the market: x-ray and laser. However, most electronic companies depend on visual inspection at 2 to 10X, using either microscope of magnifying lamp.
SMT Magazine and SMTA (Surface Mount Technology Association)
SMT magazine is an online magazine dedicated to old, latest and upcoming developments in the field of surface mount technology. It publishes news and Information for and about the global printed circuit board industry.
SMTA membership is an international network of professionals who build skills, share practical experience and develop solutions in electronic assembly technologies, including microsystems, emerging technologies, and related business operations.
Implementing SMT in Production Line for Manufacturing
Implementing SMT in production line needs some study and research. Without proper study and research, any SMT production line bears the risk of failure and increased cost. There are SMT experts who offer classes and tutorial on proper implementation and use of SMT.
Not all electronic components are available in SMD. So thru-hole soldering technology is bound to exist. Combining SMT and thru-hole technology for successful PCB assembly is a challenge. So, manufacturers and engineers should do their study and research and take expert classes to avoid failure and increased cost.
Santosh Das - Hi ! I am Santosh Das, an electronics engineer and a professional blogger. Having worked as area manager for an electronics company ...
