SMT Manufacturing: Everything You Need to Know

Introduction

Surface mount technology (SMT) revolutionizes electronic assembly by placing electronic components, known as surface mount devices (SMD), directly onto a printed circuit board (PCB). Leading to significant savings in cost and enhanced quality, SMT has become indispensable in the electronics industry.

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What is Surface Mount Technology (SMT)?

Surface mount technology (SMT) stands as a cornerstone in the assembly and production of electronic devices. By directly mounting components onto the PCB's surface, the method enables automated production, yielding efficient and high-quality results. These components, known as surface-mount devices (SMD), are soldered directly through reflow soldering, bypassing the drilling of lead holes required in Through-Hole Technology.

Initially called Planar Mounting, SMT was pioneered by IBM in the 1960s for small-scale computer production. However, it wasn't until 1986 that it gained significant traction, reaching 10% market popularity. By 1990, the majority of high-tech printed circuit assemblies incorporated surface-mounted devices. The small tabs designed on SMT components for solder application facilitated the mounting of these components on PCBs, significantly streamlining assembly.[1]

Electronic manufacturing companies predominantly use automated machines to carry out the SMT assembly process due to the high level of precision required. These machines enhance efficiency, particularly for large-scale productions.[2] Modern electronics, from toys to smartphones, extensively employ SMT components due to their smaller size, making devices more compact and aesthetically appealing.[3]

SMT Manufacturing Process

The SMT manufacturing process involves three main stages: solder paste printing, component placement, and reflow soldering. Each stage is crucial for a successful assembly.

1. SMC and PCB Preparation

In this initial stage, Surface Mount Components (SMCs) are selected, and the PCB is designed. The PCB generally features flat solder pads made from materials like silver, tin-lead, or gold-plated copper, supporting the component pins such as transistors and chips. A stencil is used to ensure accurate solder paste placement according to the predetermined positions on the PCB. All materials must be rigorously inspected for any flaws before proceeding.

2. Solder Paste Printing

During this critical phase, solder paste is applied using a stencil and a squeegee at an angle of 45° to 60°. The solder paste, a mix of powdered metal solder and flux, temporarily holds the surface mount components in place. To ensure proper connections, every pad must be adequately coated with solder paste before entering the reflow oven.

3. Components Placement

Pick-and-place machines are employed to mount components on the PCB accurately. These machines use a vacuum or gripper nozzle to place components precisely on the conveyor-carried PCB, with some machines capable of placing up to 80,000 components per hour.

4. Reflow Soldering

After components are placed, the PCB undergoes reflow soldering, passing through zones in the reflow soldering oven: preheat, soak, reflow, and cooling. Each temperature zone ensures the solder paste melts and forms secure connections between components and the PCB.

5. Cleaning and Inspection

Post-soldering, the PCB is cleaned and rigorously inspected for defects using various methods, including magnifying lenses, AOI (Automated Optical Inspection), flying probe testing, and X-ray inspection. This ensures high quality and reliability.

SMT: Pros and Cons

SMT offers numerous advantages for PCB assembly and electronic manufacturing:

• Enables the use of smaller components
• Facilitates increased automation
• Provides flexibility in PCB design
• Enhances reliability and performance
• Reduces manual intervention
• Results in smaller, lighter boards
• Allows the use of both sides of the PCB
• Can be combined with through-hole components
• Increases component density
• Lowers material costs
• Simplifies production and reduces costs[4]

However, SMT also has its downsides:

• Requires high precision in soldering technology
• Components are fragile and can easily be damaged
• Visual inspection is challenging and often requires automated systems
• Significant investment in equipment is needed
• High training and learning costs
• Continuously evolving technology demands staying updated[5]

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SMT vs SMD

People often confuse SMT (Surface Mount Technology) and SMD (Surface Mount Device). It's crucial to understand the difference: SMT refers to the technology and process of placing and soldering components onto a PCB, whereas SMD refers to the actual components used in this technology. This distinction helps in appreciating the efficiency and functionality that SMT technologies offer. Smaller SMDs enable quicker, cost-effective production of highly functional devices.[6]

Closing Thoughts

SMT’s ability to deliver smaller, quicker, and lighter electronic assemblies makes it essential in modern electronics manufacturing. The industry's move towards high automation has optimized resource use and time. With ongoing advancements, SMT continues to hold a vital position in the electronics manufacturing landscape.

References

1. SCRIBD. Surface-Mount Technology: History. 2019.[cited 2022 Jun 8]. Available from: https://www.scribd.com/document/106437192/SMD
2. Das S. SMT Machine and SMT Machine Manufacturers. 2021 [cited 2022 Jun 8]. Available from: http://www.electronicsandyou.com/smt-machine-and-smt-machine-manufacturers.html
3. Geospace Technology. SMT ASSEMBLY TECHNOLOGY: ALL YOU NEED TO KNOW. 2021.[cited 2022 Jun 9]. Available from: https://geospacemfg.com/blog/smt-assembly-technology/
4. Blog Industry News. Top Benefits of Surface-mount Technology (SMT) PCB Assembly. 2020. [cited 2022 Jun 9]. Available from: https://www.pcbnet.com/blog/benefits-surface-mount-technology-smt-pcb-assembly/
5. PCBWay. Advantages and Disadvantages of Surface Mounting Technology. 2019.[cited 2022 Jun 9]. Available from: https://www.pcbway.com/blog/PCB_Assembly/Advantages_and_Disadvantages_of_Surface_Mounting_Technology.html

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