SMT (Surface Mount Technology) is a packaging technology in electronics that mounts electronic components on the surface of a printed circuit board / Printed Wiring Board (PCB / PWB) instead of inserting them through holes of the board. SMT or Surface Mount Technology is relatively new technology in electronics and provides state-of-art, miniature electronics products at reduced weight, volume and cost.
History of SMT is rooted in the technology of Flat Packs (FP) and hybrids of 1950s and 1960s. But for all practical purposes, today’s SMT can be considered to be a continually evolving technology. Currently the use of Fine Pitch, Ultra Fine Pitch (UFP) and Ball Grid Arrays (BGAs) are becoming even more common.
Even the next level of packaging technologies such as Chip-on-Board (COB), Tape-Automated Bonding (TAB), and Flip Chip Technologies are gaining widespread acceptance. Multichip Modules (MCMs) using wire bond, TAB, or Flip Chip are used to achieve the highest performance possible but with a cost premium.
Here I explain SMT acronyms and abbreviations.
SMT Dictionary
- A-Stage: The condition of low molecular weight of a resin polymer during which the resin is readily soluble and fusible.
- Anisotropic: A material fillet with a low concentration of large conductive particles designed to conduct electricity in the Z axis but not the X or Y axis. Also called Z axis adhesive.
- Annular Ring: The conductive material around a drilled hole.
- Aqueous Cleaning: A water-based cleaning methodology which may include the addition of the following chemicals: neutralizers, saponifiers, and surfactants. May also use DI (Deionized) water only.
- Aspect Ratio: A ratio of the thickness of the board to its preplated diameter. A via hole with aspect ratio greater than 3 may be susceptible to cracking.
- Azeotrope: A blend of two or more polar and non polar solvents that behaves as a single solvent or remove polar and nonpolar contaminants. It has one boiling point like any other single component solvent, but it boils at a lower temperature than either of its constituents. The constituents of the azeotrope cannot be separated.
- B. Stage: Sheet material (e.g., glass fabric) impregnated with a resin cured to an intermediate stage.
- Ball Grid Array (BGA): Integrated circuit package in which the input and output points are solder balls arranged in a grid pattern.
- Blind Via: A via extended from an inner layer to the surface.
- Blowhole: A large void in a solder connection created by rapid outgassing during the soldering process.
- Bridge: Solder that bridges across two conductors that should not be electrically connected, thus causing an electrical short.
- Buried Via: A via hole connecting internal layers that does not extend to the board surface.
- Butt Joint: A surface mount device lead that is sheared, so that the end of the leads contacts the board and land pattern.
- C-Stage Resin: A resin in a final stage of cure.
- Capillary Action: The combination of force, adhesion, and cohesion which causes liquids such as molten metal to flow between closely spaced solid surfaces against the force of gravity.
- Castellation: Metallized semicircular radial features on the edges of LCCC’s that interconnect conducting surfaces. Castellations are typically found on four edges of a leadless chip carrier. Each lies within the termination area for direct attachment to the land patterns.
- CFC: Chlorinated fluorocarbon, cause depletion of ozone layer and scheduled for restricted use by the environmental protection agency. CFC’s are used in air conditioning, foam insulation and solvents, etc.
- Characteristic Impedance: The voltage-to-current ratio in a propagation wave, i.e., the impedance which is offered to the wave at any point of the line. In printed wiring its value depends on the width of the conductor to ground plane(s) and the dielectric constant to the media between them.
- Chip Component: Generic term for any two-terminal leadless surface mount passive devices, such as resistors and capacitors.
- Chip-on-Board Technology: Generic term for any component assembly technology in which an unpackaged silicon die is mounted directly on the printed wiring board. Connections to the board can be made by wire bonding, tape automated bonding (TAB), or flip-chip bonding.
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