Why SMT?
Manufacturers continuously evaluate new components and systems technologies in terms of reducing size, increasing design flexibility, improving reliability and reducing cost for systems. SMT satisfies all these requirements. It can provide size reductions of over 40%, assembly cost reductions of almost 50%, and can enhances the performance of electrical circuitry [Lea, 1988].
SMT Reduces Size and weight
The increased density of components can lead to a higher functionality in the same space. This allows the system manufacturer to price differentiate his product in the market by carefully choosing his components.
- SMT components require less circuit board area and volume than their through-hole equivalent.
- Components can be mounted on both sides of boards.
- Lighter components with the same functionality can be significant in the
aerospace industry as well as portable consumer electronics.
SMT Increases Performance
- SMT offers better interconnectivity due to shorter paths, providing lower inductance and capacitance.
- SMT reduces the package propagation delay, which is the time the signal needs to move from one component to another. Typically the longest delays in the system are off-chip.
- Electromagnetic interference can be decreased by combining sensitive circuits on a single board and improving its Electromagnetic Induction (EMI) shield design.
SMT Improves Reliability
- The smaller and lighter construction of SMC’s allow them to resist shock and vibration better than their through-hole counterparts.
- The reduced number of PCBs and connectors improves overall reliability at the system level.
- However, SMT systems require careful attention to mechanical design to avoid overstressing the solder joints.
- The demanding nature of the SMT process has resulted in extensive automation and corresponding increases in product quality.
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SMT Reduces Cost
• Bare Boards
The use of SMT, typically, results in smaller area PCBs being used due to the reduction in the size of the components being used. In general for two functionally equivalent PCBs, one utilizing surface mount and the other using conventional through hole, the larger the PCB, the more expensive it will be. Increased density on an SMT board generally requires multiple layers as well as smaller line widths and spacings to accommodate the finer pitch components and smaller hole diameters to interconnect the layers. The only time a hole is required is to carry the signal to another layer whereas with through hole components there must be a hole for each lead of each component. In some cases through hole PCB’s may require more layers because there are more larger holes which means there will be less room on the inner layers for circuit routing increasing the layer count.• Processing
Surface mount components have almost all been designed for automatic assembly. Many unusually shaped, through-hole components, called odd- formed components, which were designed for hand assembly, can now be placed automatically as well. Automated assembly of surface mount assemblies can be done using one flexible automated placement machine whereas several machines may be required for the various through hole components.
As more types of components become available in a surface mount format, correspondingly fewer components are available in through-hole configuration forcing the cost of many SMC devices down. While through-hole components can be automatically inserted, the combined equipment, floor space and processing costs are higher.
• Factory Operating
Fewer types of assembly machines are required for an SMC assembly line and they often requires less floor space. Automated SMT assembly lines are considerably more productive than PTH assembly tools. Thus throughput is raised considerably with SMT manufacturing and the cost per unit of assembly is greatly reduced.
SMT Increases Flexibility
- SMT provides a wider range of packaging possibilities than insertion mount technology.
- SMT allows for the use of both surface mount and insertion mount devices in the same assembly.
SMT Eases Handling And Storage Space Needs
Surface mount components are easy to handle due to the various storage formats in which they are shipped and presented to the pick and place machines. Tape and reel, cartridge, sticks, magazines, and matrix trays allow effective and safe handling and shipping. The storage formats have the following features:
- Large number of components per packing unit resulting in less frequent loading of the tools.
- Small amount of packing materials per component resulting in lower shipping and inventory costs.
- Protection against transport and handling damage.
- Standardization, Definite orientation of the components.
- Protection against electrostatic discharge resulting in fewer defective systems
and rework.
- Compatible with highly automated equipment.
Electronic Industry Organizations and Groups
Uniform Standards for Surface Mount Technology are still under development in the USA, Europe and Japan. Although much has been accomplished, there is still no single set of industry guidelines. However, efforts are being taken to resolve this problem. For example, there was inconsistency in the standards set by the IPC and the EIA. As this was recognized, they have joined forces to set up a council called Surface Mount Council, to coordinate the various standards between the users and the developers of these standards. These documents have a J-STD- xxx designation. Moreover, other organizations like the International Microelectronics and Packaging Society (IMAPS) are working together on the technical issues in the PCB industry. These developments are promising and should lead to a common industrial standard in the near future.
IPC- Association Connecting Electronics Industries
2215 Sanders Road Northbrook, IL 60062-6135 USA Tel: (847) 509-9700 Fax – (847) 509-9798
Internet: www.ipc.orgIn 1999, IPC changed its name from Institute of Interconnecting and Packaging Electronic Circuits to IPC. The new name is accompanied with an identity statement, Association Connecting Electronics Industries.
IPC started in 1957 as the Institute for Printed Circuits. As more electronics assembly companies became involved with the association, the name was changed to the Institute for Interconnecting and Packaging Electronic Circuits. In the 1990s, most people in the industry could not remember the name and/or didn’t agree on what the words in the name meant. In addition, the leaders from government or other business groups could not understand the name either.
