The most comprehensive explanation of SMT surface mounting technology
SMT is the abbreviation of surface mount technology
SMT is no longer a new technology in the electronic field. The technology provides the latest micro electronic products with reduced weight, volume and cost. This SMT explanation will help you learn and understand the terms and meanings used in this SMT technology.
What is SMT?
SMT (Surface Mount Technology) is a packaging technology in electronic products. Electronic components can be installed on the surface of the printed circuit board/printed circuit board (PCB/PWB) instead of inserting them through the holes of the circuit board.
The history of SMT originates from Flat Packs (FP) and hybrid technology in 1950s and 1960s. But for all practical purposes, today’s SMT can be considered an evolving technology. At present, the use of fine pitch, ultra-fine pitch (UFP) and ball grid array (BGA) is becoming more and more popular.
Even higher level packaging technologies, such as onboard chip (COB), tape automatic bonding (TAB) and flip chip technology, have also been widely recognized. Using wire bonding, TAB or Flip Chip Multi Chip Modules (MCM) can achieve the highest possible performance at a higher cost.
Here, I explained the abbreviations and abbreviations of SMT.
A-stage: the low molecular weight state of the resin polymer, during which the resin is easy to dissolve and melt.
Anisotropy: The low concentration of a material fish fillet is designed to conduct the electricity of large conductive particles in the Z axis rather than the X or Y axis. Also called Z-axis glue.
Ring: conductive material surrounding the borehole.
Water cleaning: A water-based cleaning method that may include the addition of the following chemicals: neutralizers, saponifiers, and surfactants. It is also possible to use only deionized water.
Length width ratio: the ratio of the thickness of the plate to its pre plated diameter. Through holes with a length diameter ratio greater than 3 may produce cracks.
Azeotrope: A mixture of two or more polar and non-polar solvents, which can act as a single solvent or remove polar and non-polar pollutants. Like any other single component solvent, it has a boiling point, but the boiling point is lower than that of any one of its components. The components of the azeotrope cannot be separated.
B. Stage: sheet impregnated with resin cured to intermediate stage (e.g. glass fiber).
Ball grid array (BGA): An integrated circuit package in which the input and output points are solder balls arranged in a grid pattern.
Blind hole: Through hole extending from the inner layer to the surface.
Porosity: large gap formed in welding connection due to rapid degassing during welding.
Bridge: Solder across two conductors that should not be electrically connected, resulting in electrical short circuit.
Embedded hole: According to SMT dictionary, embedded hole is a through-hole connecting the internal layer that does not extend to the surface of the circuit board.
Butt joint: In the SMT dictionary, the butt joint is a sheared surface mount device (SMD) lead, so the end of the lead contacts the circuit board and pad pattern.
C-stage resin: resin in the final curing stage.Capillary action: The combination of force, adhesion, and cohesion that causes liquids such as molten metal to flow between closely spaced solid surfaces against gravity.
Castle shape: The metallized semicircle radial feature on the edge of LCCC makes the conductive surfaces connect with each other. The castle shape usually appears on the four edges of the lead-free chip carrier. Each is located in the terminal area and is used to connect directly to the pad pattern.
CFC: Chlorinated fluorocarbons, which will consume the ozone layer, are planned to be restricted by environmental protection agencies. CFCs are used in air conditioners, foam insulation and solvents.
Characteristic impedance: the voltage/current ratio in the propagation wave, that is, the impedance provided to the wave at any point of the line. In a printed circuit, its value depends on the width of the conductor to the ground plane and the dielectric constant of the medium between them.
Chip assembly: A generic term for any surface mounted passive device with no leads at either end, such as SMD resistor and SMD capacitor.
Chip on board technology: the general term for any component assembly technology, in which the unpacked silicon chip is directly installed on the printed circuit board. It can be connected to the board by wire bonding, tape automatic bonding (TAB) or flip chip bonding.
CLCC: Ceramic lead chip carrier.
Cold solder joint: In the SMT dictionary, the cold solder joint is a solder joint. Due to insufficient heat or excessive impurities in the solder, the wettability is poor, and the appearance is gray and porous.
Column Grid Array (CGA): An integrated circuit (IC) package in which the input and output points are high-temperature solder cylinders or columns arranged in a grid pattern.
Assembly face: In through-hole technology, a term used to represent PWB assembly face.
Condensation inert heating: a general term that refers to condensation heating, in which the parts to be heated are immersed in hot, relatively oxygen free steam. Parts that are cooler than steam condense steam on the parts and transfer its latent heat of vaporization to the parts. Also called gas phase welding.
Restrained core substrate: a composite printed circuit board composed of epoxy glass layer of PCB material and low thermal expansion core material (such as copper interior copper, graphite epoxy resin and aramid fiber epoxy resin). The core constrains the expansion of the outer layer to match the expansion coefficient of the ceramic chip carrier.
Contact angle: the wetting angle between the weld corner and the terminal or pad pattern. The contact angle is measured by constructing a line tangent to the solder corner line, which passes through the origin at the intersection between the solder corner line and the terminal or pad shape. Contact angle (positive wetting angle) less than 90 ° C is acceptable. Contact angle (negative wetting angle) less than 90 ° C is not acceptable.
Control Chart: A chart that controls process performance over time. The trend in the chart is used to identify process problems that may require corrective action to control the process.
Coplanarity: The maximum distance between the lowest and highest pins when the package is placed on a perfectly flat surface. The maximum coplanarity of peripheral package is 0.004 inch, and that of BGA package is 0.008 inch.
Cracking: The internal condition that occurs in the laminated substrate, in which the glass fiber separates from the resin at the braided intersection. This occurs in the form of connected white spots (“crosses”) below the surface of the substrate, usually related to mechanically induced stresses.
CTE (coefficient of thermal expansion): the ratio of size change to unit temperature change. CTE is usually expressed in ppm/℃.
Delamination: the separation between layers inside the substrate or between the substrate and the conductive foil or both.
Dendritic growth: the growth of metal wires between conductors in the presence of condensed water and electric bias. (Also called “whisker”.)