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Glossary of terms

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Term Definition
halides   Compounds containing halogens (the elements fluorine, chlorine, bromine, iodine or astatine), most usually chlorine and bromine. Within soldering, the term is usually used to refer to halogen salts (especially ammonium chloride and methyl ammonium chloride) which are activators within the flux system. Residues of these materials are corrosive, and often need to be removed if present in high concentrations. Most current fluxes are ‘halide-free’.
halogen-free laminate  Brominated compounds (halogenated compounds) have traditionally been used in various forms as flame retardants in PCB laminates. Brominated compounds (PBB, PBDE) have been found to react to form dioxins and furans during combustion. WEEE and RoHS have required the elimination of PBBs, PBDEs and TBBAs and as a result PCB laminate makers have created halogen-free laminates.
haloing   Mechanically induced fracturing or delamination on or below the surface of the base material; it is usually exhibited by a light area around holes, other machined areas, or both.
hardener   A chemical added to a thermosetting resin to assist its cure.
hard-wired interconnections   Circuit connections using wire as opposed to etched interconnections.
HASL   (Hot-Air Solder Levelling). A process used to solder coat a board, in which the board is dipped first in flux and then in solder, with jets of heated high velocity air being used to blow any excess molten material from the boards, especially out of the plated through-holes, so as to provide as flat a surface as possible. There is a trade-off between solder thickness and the flatness of the solder coat, because solder will always form a convex surface when melted.
hazardous waste   Defined as the most harmful wastes to people and the environment.
HDI   (High Density Interconnect). Ultra fine-geometry multi-layer PCB constructed with conductive microvia connections. These boards also usually include buried and/or blind vias and are made by sequential lamination.
header   The portion of a connector assembly which is mounted on a printed circuit.
heat removal mechanisms   Heat may be transferred from a surface by any or all of three mechanisms: conduction, convection, and radiation.
heat sink   A device that aids in the removal of heat from electronic equipment, and is particularly important when heat is generated in a small area, or when devices such as power transistors, rectifiers and microprocessors are operated. Heat sinks may be added to components, or to complete assemblies. Typically they are made of metal with high thermal conductivity, and the removal of heat may be assisted by built-in fans as well as depending on natural or forced convection.
heat-and-pull   A desoldering technique using a soldering iron equipped with a device that heats, grasps and pulls component leads to be removed.
hermaphroditic connectors   Contacts and mouldings, which can be used as both male and female types (that is, they will plug into each other).
hermetic   Airtight sealing of an object.
HHASL   (Horizontal Hot-Air Solder Levelling). A process used to solder coat a board, in which the board is processed through a flux roller then a solder pot in a conveyorized fashion, with jets of heated high velocity air being used to blow any excess molten material from the boards, especially out of the plated through-holes, so as to provide as flat a surface as possible. Solder thickness and the flatness or planarity of the solder coat is more uniform and controlled versus typical vertical HASL
high insertion force   Refers to contacts, which, due to their design and function, require a high force to plug together. Used mainly in high-current or low-cost connectors.
high-density interconnect   (HDI). The ‘density’ of interconnections is a measure of the average amount of circuitry package in a given area of assembly. This can be in terms of the length of conductor within a given area, or the number of component/I/Os terminated in that area. Where boards have average I/O counts above 200 per square inch of area, they are currently treated as high-density designs.
hi-pot test   The definition is a generic term for tests at ‘high potential’, intended to provide assurance that a circuit will operate safely, with the required isolation between components. Whilst the bottom limit for a hi-pot test is 40 volts, many similar tests are carried out at substantially higher voltages. Always with these tests, you should take precautions to protect the operator from exposure to high voltage.
hole breakout   A condition in which a hole is not completely surrounded by its associated land.
hole density   The quantity of holes in a unit area of a printed board.
hole pattern   The arrangement of all holes in a printed board with respect to a reference point.
hot gas   A method of rework for SMT boards which uses a stream of hot gas to melt the solder connection for component removal.
hot plugging   Adding or removing components or sub-assemblies to a system whilst it is powered up (hot). This needs to happen without causing damage to any of the circuitry and without significantly interrupting the system. Hot plugging is also called line insertion or live line connection.
housing   The insulating body, usually a plastic moulding which holds the electrical contacts. Housings are also referred to as insulators, dielectrics or shells.
hybrid (micro)circuit   A generic term for a range of technologies which integrate passive and active components. Most commonly refers to ceramic substrates patterned with precious metal interconnect and resistor materials, on which chip ceramic capacitors and integrated circuits are soldered, resin bonded and/or wire bonded. A frequent base for Chip-On-Board assembly.
hybrid PCB   A PCB that consists of a combination of high performance laminates/materials to facilitate operation in extreme environments.