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’.

hazardous waste: See Special waste. Defined by EU legislation as the most harmful wastes to people and the environment.

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.

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).

high-density interconnect 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.

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-speed circuitry

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.

hoods (see covers)

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.

HPGL Hewlett-Packard Graphics Language, a text-based data structure of pen-plot files which are used to drive Hewlett-Packard pen plotters. Although Hewlett-Packard no longer makes pen plotters, the large-format dot matrix printers which replaced them can also be driven by HPGL.

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.