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Metal electrode leadless face (MELF) is a type of leadless cylindrical electronic surface mount device that is metallized at its ends. MELF devices are usually diodes and resistors.
Vacuum deposition is a family of processes used to deposit layers of material atom-by-atom or molecule-by-molecule on a solid surface. These processes operate at pressures well below atmospheric pressure. The deposited layers can range from a thickness of one atom up to millimeters, forming freestanding structures. Multiple layers of different materials can be used, for example to form optical coatings. The process can be qualified based on the vapor source; physical vapor deposition uses a liquid or solid source and chemical vapor deposition uses a chemical vapor.
The EN 140401-803 and DO-213 standards describe multiple MELF components.
Because of their cylindrical shape and small size, in some cases these components can easily roll off the workbench or circuit board before they have been soldered into place. As such, there is a joke which suggests an alternate meaning for the acronym: Most End up Lying on the Floor. Additionally, MELF components are sometimes called a "roll away" package.
During automated SMT pick-and-place, this happens mostly if the mechanical pressure of the SMD placer nozzle is too low. If the MELF components are placed into the solder paste with enough pressure, then this problem can be minimized. Care must be taken with glass diodes which are less mechanically robust than resistors and other MELF components.
Also, when building up PCBs via manual assembly using tweezers (e.g., for prototyping) then the pressure at the end of tweezers can often cause a MELF component to slip and shoot out the ends, thereby making their placement more difficult, compared to other flat component packages.
Another reason for the nickname of MELF components is that most production engineers do not like to use MELF nozzles on a SMT pick-and-place machine. For them it is waste of time to change from flat nozzles to MELF nozzles. For MICRO-MELF and MINI-MELF most SMD placers are able to use flat chip nozzles if the vacuum is high enough; i.e., higher than for flat chip components. For MELFs with the case size of 0207 or less, it is recommended to use the original MELF nozzle supplied with the SMT machine. Each supplier of such SMD pick-and-place machines offers these types of nozzles.
In order to overcome some of the difficulties encountered when mounting these devices, there are also variants with square electrodes (e.g. SQ MELF, QuadroMELF and B-MELF). These variants are mainly used in semiconductor diodes for applications where the high-reliability of hermetically sealed voidless-glass packages is required.
These handling difficulties prompted development of alternative SMT packages for common MELF components (like diodes) where the power handling capability needed to be similar to MELF components (superior to low-power 0805/0603, etc. SMT components) but with improved automated pick-and-place handling characteristics.This resulted in various squared-off packages with fold-over contacts, similar to rectangular inductor/tantalum capacitor packages.
Despite their handling difficulties, and in the particular case of MELF resistors, they are still widely used in high-reliability and precision applications where their predictable characteristics (e.g., low failure rate with well-defined failure modes) as well as their higher performance in terms of accuracy, long-term stability, moisture resistance, high-temperature operation far outweigh their disadvantages.
In microelectronics, a dual in-line package, or dual in-line pin package (DIPP) is an electronic component package with a rectangular housing and two parallel rows of electrical connecting pins. The package may be through-hole mounted to a printed circuit board (PCB) or inserted in a socket. The dual-inline format was invented by Don Forbes, Rex Rice and Bryant Rogers at Fairchild R&D in 1964, when the restricted number of leads available on circular transistor-style packages became a limitation in the use of integrated circuits. Increasingly complex circuits required more signal and power supply leads ; eventually microprocessors and similar complex devices required more leads than could be put on a DIP package, leading to development of higher-density packages. Furthermore, square and rectangular packages made it easier to route printed-circuit traces beneath the packages.
A printed circuit board (PCB) mechanically supports and electrically connects electronic components or electrical components using conductive tracks, pads and other features etched from one or more sheet layers of copper laminated onto and/or between sheet layers of a non-conductive substrate. Components are generally soldered onto the PCB to both electrically connect and mechanically fasten them to it.
Surface-mount technology (SMT) is a method for producing electronic circuits in which the components are mounted or placed directly onto the surface of printed circuit boards (PCBs). An electronic device so made is called a surface-mount device (SMD). In industry, it has largely replaced the through-hole technology construction method of fitting components with wire leads into holes in the circuit board. Both technologies can be used on the same board, with the through-hole technology used for components not suitable for surface mounting such as large transformers and heat-sinked power semiconductors.
Tweezers are small tools used for picking up objects too small to be easily handled with the human fingers. The word is most likely derived from tongs, pincers, or scissors-like pliers used to grab or hold hot objects since the dawn of recorded history. In a scientific or medical context they are normally referred to as forceps.
In electronics, desoldering is the removal of solder and components from a circuit board for troubleshooting, repair, replacement, and salvage.
Rework is the term for the refinishing operation or repair of an electronic printed circuit board (PCB) assembly, usually involving desoldering and re-soldering of surface-mounted electronic components (SMD). Mass processing techniques are not applicable to single device repair or replacement, and specialized manual techniques by expert personnel using appropriate equipment are required to replace defective components; area array packages such as ball grid array (BGA) devices particularly require expertise and appropriate tools. A hot air gun or hot air station is used to heat devices and melt solder, and specialised tools are used to pick up and position often tiny components.
In electronics, a lead is an electrical connection consisting of a length of wire or a metal pad (SMD) that is designed to connect two locations electrically. Leads are used for many purposes, including: transfer of power; testing of an electrical circuit to see if it is working, using a test light or a multimeter; transmiting information, as when the leads from an electrocardiograph, or ECG are attached to a person's body to transmit information about their heart rhythm; and sometimes to act as a heatsink. The tiny leads coming off through-hole components are also often called pins.
SMT component placement systems, commonly called pick-and-place machines or P&Ps, are robotic machines which are used to place surface-mount devices (SMDs) onto a printed circuit board (PCB). They are used for high speed, high precision placing of broad range of electronic components, like capacitors, resistors, integrated circuits onto the PCBs which are in turn used in computers, consumer electronics as well as industrial, medical, automotive, military and telecommunications equipment. Similar equipment exists for through hole components. This type of equipment is sometimes also used to package microchips using the flip chip method.
A hybrid integrated circuit (HIC), hybrid microcircuit, hybrid circuit or simply hybrid is a miniaturized electronic circuit constructed of individual devices, such as semiconductor devices and passive components, bonded to a substrate or printed circuit board (PCB). A PCB having components on a Printed Wiring Board (PWB) is not considered a hybrid circuit according to the definition of MIL-PRF-38534.
Flat no-leads packages such as quad-flat no-leads (QFN) and dual-flat no-leads (DFN) physically and electrically connect integrated circuits to printed circuit boards. Flat no-leads, also known as micro leadframe (MLF) and SON, is a surface-mount technology, one of several package technologies that connect ICs to the surfaces of PCBs without through-holes. Flat no-lead is a near chip scale plastic encapsulated package made with a planar copper lead frame substrate. Perimeter lands on the package bottom provide electrical connections to the PCB. Flat no-lead packages include an exposed thermal pad to improve heat transfer out of the IC. Heat transfer can be further facilitated by metal vias in the thermal pad. The QFN package is similar to the quad-flat package (QFP), and a ball grid array (BGA).
The thermal copper pillar bump, also known as the "thermal bump", is a thermoelectric device made from thin-film thermoelectric material embedded in flip chip interconnects for use in electronics and optoelectronic packaging, including: flip chip packaging of CPU and GPU integrated circuits (chips), laser diodes, and semiconductor optical amplifiers (SOA). Unlike conventional solder bumps that provide an electrical path and a mechanical connection to the package, thermal bumps act as solid-state heat pumps and add thermal management functionality locally on the surface of a chip or to another electrical component. The diameter of a thermal bump is 238 μm and 60 μm high.
Thick-film technology is used to produce electronic devices such as surface mount devices, hybrid integrated circuits and sensors.
A semiconductor package is a metal, plastic, glass, or ceramic casing containing one or more discrete semiconductor devices or integrated circuits. Individual components are fabricated on semiconductor wafers before being diced into die, tested, and packaged. The package provides a means for connecting the package to the external environment, such as printed circuit board, via leads such as lands, balls, or pins; and protection against threats such as mechanical impact, chemical contamination, and light exposure. Additionally, it helps dissipate heat produced by the device, with or without the aid of a heat spreader. There are thousands of package types in use. Some are defined by international, national, or industry standards, while others are particular to an individual manufacturer.
The 1N400x series is a family of popular 1 A general-purpose silicon rectifier diodes commonly used in AC adapters for common household appliances. Its blocking voltage varies from 50 volts (1N4001) to 1000 volts (1N4007). This JEDEC device number series is available in the DO-41 axial package, and similar diodes are available in SMA and MELF surface mount packages.
Quadracs are a special type of thyristor which combines a "diac" and a "triac" in a single package. The diac is the triggering device for the triac. Thyristors are four-layer (PNPN) semiconductor devices that act as switches, rectifiers or voltage regulators in a variety of applications. When triggered, thyristors turn on and become low-resistance current paths. They remain so even after the trigger is removed, and until the current is reduced to a certain level. Diacs are bi-directional diodes that switch AC voltages and trigger triacs or silicon-controlled rectifiers (SCRs). Except for a small leakage current, diacs do not conduct until the breakover voltage is reached. Triacs are three-terminal, silicon devices that function as two SCRs configured in an inverse, parallel arrangement. They provide load current during both halves of the AC supply voltage. By combining the functions of diacs and triacs, quadracs eliminate the need to buy and assemble discrete parts.
Electronic components have a wide range of failure modes. These can be classified in various ways, such as by time or cause. Failures can be caused by excess temperature, excess current or voltage, ionizing radiation, mechanical shock, stress or impact, and many other causes. In semiconductor devices, problems in the device package may cause failures due to contamination, mechanical stress of the device, or open or short circuits.
In electronics, a chip carrier is one of several kinds of surface-mount technology packages for integrated circuits. Connections are made on all four edges of a square package; Compared to the internal cavity for mounting the integrated circuit, the package overall size is large.
Component placement is an electronics manufacturing process that places electrical components precisely on printed circuit boards (PCBs) to create electrical interconnections between functional components and the interconnecting circuitry in the PCBs (leads-pads). The component leads must be accurately immersed in the solder paste previously deposited on the PCB pads. The next step after component placement is soldering.
Chip on board is the method of manufacturing where integrated circuits are wired and bonded directly to a printed circuit board. By eliminating the packaging of individual semiconductor devices, the completed product can be more compact, lighter, and less costly. In some cases chip on board construction improves the operation of radio frequency systems by reducing the inductance and capacitance of integrated circuit leads. Chip on board effectively merges two levels of electronic packaging, level 1 (components) and level 2, and may be referred to as a "level 1.5"