Reflow oven

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A reflow oven is a machine used primarily for reflow soldering of surface mount electronic components to printed circuit boards (PCB).

Reflow soldering Electronics soldering process

Reflow soldering is a process in which a solder paste is used to temporarily attach one or thousands of tiny electrical components to their contact pads, after which the entire assembly is subjected to controlled heat. The solder paste reflows in a molten state, creating permanent solder joints. Heating may be accomplished by passing the assembly through a reflow oven or under an infrared lamp or by soldering individual joints [unconventionally] with a desoldering hot air pencil.

Printed circuit board Board to support and connect electronic components

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.

Contents

Types of reflow ovens

Infrared and convection ovens

A convection industrial reflow oven. Mark5 1826 Reflow Oven.jpg
A convection industrial reflow oven.
Example of reflow soldering thermal profile. RSS Components of a Profile1.svg
Example of reflow soldering thermal profile.

The oven contains multiple zones, which can be individually controlled for temperature. Generally there are several heating zones followed by one or more cooling zones. The PCB moves through the oven on a conveyor belt, and is therefore subjected to a controlled time-temperature profile.[ clarification needed ]

Conveyor belt material-handling equipment

A conveyor belt is the carrying medium of a belt conveyor system. A belt conveyor system is one of many types of conveyor systems. A belt conveyor system consists of two or more pulleys, with an endless loop of carrying medium—the conveyor belt—that rotates about them. One or both of the pulleys are powered, moving the belt and the material on the belt forward. The powered pulley is called the drive pulley while the unpowered pulley is called the idler pulley. There are two main industrial classes of belt conveyors; Those in general material handling such as those moving boxes along inside a factory and bulk material handling such as those used to transport large volumes of resources and agricultural materials, such as grain, salt, coal, ore, sand, overburden and more.

The heat source is normally from ceramic infrared heaters, which transfers the heat to the assemblies by means of radiation. Ovens which also use fans to force heated air towards the assemblies (which are usually used in combination with ceramic infrared heaters) are called infrared convection ovens.

Heat energy transfer process, or its amount (and direction), that is associated with a temperature difference

In thermodynamics, heat is energy in transfer to or from a thermodynamic system, by mechanisms other than thermodynamic work or transfer of matter. The mechanisms include conduction, through direct contact of immobile bodies, or through a wall or barrier that is impermeable to matter; or radiation between separated bodies; or isochoric mechanical work done by the surroundings on the system of interest; or Joule heating by an electric current driven through the system of interest by an external system; or a combination of these. When there is a suitable path between two systems with different temperatures, heat transfer occurs necessarily, immediately, and spontaneously from the hotter to the colder system. Thermal conduction occurs by the stochastic (random) motion of microscopic particles. In contrast, thermodynamic work is defined by mechanisms that act macroscopically and directly on the system's whole-body state variables; for example, change of the system's volume through a piston's motion with externally measurable force; or change of the system's internal electric polarization through an externally measurable change in electric field. The definition of heat transfer does not require that the process be in any sense smooth. For example, a bolt of lightning may transfer heat to a body.

Radiation Waves or particles propagating through space or through a medium, carrying energy

In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or through a material medium. This includes:

Some ovens are designed to reflow PCBs in an oxygen-free atmosphere. Nitrogen (N2) is a common gas used for this purpose. This minimizes oxidation of the surfaces to be soldered. The nitrogen reflow oven takes a few minutes to reduce Oxygen concentration to acceptable levels within the chamber. Thus nitrogen ovens typically have nitrogen injection in at all times which decreases defect rates. [1]

Nitrogen Chemical element with atomic number 7

Nitrogen is the chemical element with the symbol N and atomic number 7. It was first discovered and isolated by Scottish physician Daniel Rutherford in 1772. Although Carl Wilhelm Scheele and Henry Cavendish had independently done so at about the same time, Rutherford is generally accorded the credit because his work was published first. The name nitrogène was suggested by French chemist Jean-Antoine-Claude Chaptal in 1790, when it was found that nitrogen was present in nitric acid and nitrates. Antoine Lavoisier suggested instead the name azote, from the Greek ἀζωτικός "no life", as it is an asphyxiant gas; this name is instead used in many languages, such as French, Russian, Romanian and Turkish, and appears in the English names of some nitrogen compounds such as hydrazine, azides and azo compounds.

Vapour phase oven

The heating of the PCBs is sourced by thermal energy emitted by the phase transition of a heat transfer liquid (e. g. PFPE) condensing on the PCBs. The liquid used is chosen with a desired boiling point in mind to suit the solder alloy to be reflowed.

Phase transition transitions between solid, liquid and gaseous states of matter, and, in rare cases, plasma

The term phase transition is most commonly used to describe transitions between solid, liquid, and gaseous states of matter, as well as plasma in rare cases. A phase of a thermodynamic system and the states of matter have uniform physical properties. During a phase transition of a given medium, certain properties of the medium change, often discontinuously, as a result of the change of external conditions, such as temperature, pressure, or others. For example, a liquid may become gas upon heating to the boiling point, resulting in an abrupt change in volume. The measurement of the external conditions at which the transformation occurs is termed the phase transition. Phase transitions commonly occur in nature and are used today in many technologies.

Heat transfer transport of thermal energy in physical systems

Heat transfer is a discipline of thermal engineering that concerns the generation, use, conversion, and exchange of thermal energy (heat) between physical systems. Heat transfer is classified into various mechanisms, such as thermal conduction, thermal convection, thermal radiation, and transfer of energy by phase changes. Engineers also consider the transfer of mass of differing chemical species, either cold or hot, to achieve heat transfer. While these mechanisms have distinct characteristics, they often occur simultaneously in the same system.

Krytox groiup of industrial lubricants

Krytox is a registered trademark of The Chemours Company. It refers to a group of colourless synthetic lubricants (oils and greases) with a variety of applications. Invented by researchers at DuPont, Krytox oils are fluorocarbon ether polymers of polyhexafluoropropylene oxide, with a chemical formula: F−(CF(CF3)−CF2−O)n−CF2CF3, where the degree of polymerization, n, generally lies within the range of 10 to 60. These compounds are collectively known by many names including perfluoropolyether (PFPE), perfluoroalkylether (PFAE) and perfluoropolyalkylether (PFPAE). A unique identifier is their CAS registry number, 60164-51-4.

Some advantages of vapour phase soldering are:

Boiling point temperature

The boiling point of a substance is the temperature at which the vapor pressure of a liquid equals the pressure surrounding the liquid and the liquid changes into a vapor.

This is also known as condensation soldering.

Thermal profiling

Thermal profiling is the act of measuring several points on a circuit board to determine the thermal excursion it takes through the soldering process. In the electronics manufacturing industry, SPC (Statistical Process Control) helps determine if the process is in control, measured against the reflow parameters defined by the soldering technologies and component requirements. [2] [3]

Example of a modern thermal profiler Example thermal profiler.png
Example of a modern thermal profiler

See also

References and further reading

  1. Girouard, Roland. "Mark5 Reflow Oven". Heller Industries Website. Heller Industries Inc. Retrieved 28 September 2012.
  2. "Guidelines for Temperature Profiling for Mass Soldering Processes (Reflow & Wave)" (PDF). Retrieved 2019-07-01.
  3. "Modern thermal profiling device". Solderstar Website. Solderstar. Retrieved 28 September 2018.

General references

Related Research Articles

Cryogenics study of the production and behaviour of materials at very low temperatures

In physics, cryogenics is the production and behaviour of materials at very low temperatures. A person who studies elements that have been subjected to extremely cold temperatures is called a cryogenicist.

Ball grid array

A ball grid array (BGA) is a type of surface-mount packaging used for integrated circuits. BGA packages are used to permanently mount devices such as microprocessors. A BGA can provide more interconnection pins than can be put on a dual in-line or flat package. The whole bottom surface of the device can be used, instead of just the perimeter. The traces connecting the package's leads to the wires or balls which connect the die to package are also on average shorter than with a perimeter-only type, leading to better performance at high speeds.

Surface-mount technology method for producing electronic circuits

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.

Liquid air is air that has been cooled to very low temperatures, so that it has condensed into a pale blue mobile liquid. To thermally insulate it from room temperature, it is stored in specialized containers. Liquid air can absorb heat rapidly and revert to its gaseous state. It is often used for condensing other substances into liquid and/or solidifying them, and as an industrial source of nitrogen, oxygen, argon, and other inert gases through a process called air separation.

Wave soldering Electronics soldering process

Wave soldering is a bulk soldering process used in the manufacture of printed circuit boards. The circuit board is passed over a pan of molten solder in which a pump produces an upwelling of solder that looks like a standing wave. As the circuit board makes contact with this wave, the components become soldered to the board. Wave soldering is used for both through-hole printed circuit assemblies, and surface mount. In the latter case, the components are glued onto the surface of a printed circuit board (PCB) by placement equipment, before being run through the molten solder wave. Wave soldering is mainly used in soldering of through hole components.

Heating element converts electricity into heat through the process of resistive or Joule heating (electric current passing through the element encounters resistance, resulting in heating of the element; this process is independent of the direction of current flow)

A heating element converts electrical energy into heat through the process of Joule heating. Electric current through the element encounters resistance, resulting in heating of the element. Unlike the Peltier effect, this process is independent of the direction of current.

Rework (electronics) term for the refinishing operation or repair of an electronic printed circuit board (PCB) assembly

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.

A coolant is a substance, typically liquid or gas, that is used to reduce or regulate the temperature of a system. An ideal coolant has high thermal capacity, low viscosity, is low-cost, non-toxic, chemically inert and neither causes nor promotes corrosion of the cooling system. Some applications also require the coolant to be an electrical insulator.

Thermosiphon

Thermosiphon is a method of passive heat exchange, based on natural convection, which circulates a fluid without the necessity of a mechanical pump. Thermosiphoning is used for circulation of liquids and volatile gases in heating and cooling applications such as heat pumps, water heaters, boilers and furnaces. Thermosiphoning also occurs across air temperature gradients such as those utilized in a wood fire chimney or solar chimney.

Electric heating process in which electrical energy is converted to heat

Electric heating is a process in which electrical energy is converted to heat energy. Common applications include space heating, cooking, water heating and industrial processes. An electric heater is an electrical device that converts an electric current into heat. The heating element inside every electric heater is an electrical resistor, and works on the principle of Joule heating: an electric current passing through a resistor will convert that electrical energy into heat energy. Most modern electric heating devices use nichrome wire as the active element; the heating element, depicted on the right, uses nichrome wire supported by ceramic insulators.

Selective soldering

Selective soldering is the process of selectively soldering components to printed circuit boards and molded modules that could be damaged by the heat of a reflow oven or wave soldering in a traditional surface-mount technology (SMT) or Through-hole technology assembly processes.This usually follows an SMT oven reflow process; parts to be selectively soldered are usually surrounded by parts that have been previously soldered in a surface-mount reflow process, and the selective-solder process must be sufficiently precise to avoid damaging them.

Infrared heater

An infrared heater or heat lamp is a body with a higher temperature which transfers energy to a body with a lower temperature through electromagnetic radiation. Depending on the temperature of the emitting body, the wavelength of the peak of the infrared radiation ranges from 780 nm to 1 mm. No contact or medium between the two bodies is needed for the energy transfer. Infrared heaters can be operated in vacuum or atmosphere.

Industrial oven

Industrial ovens are heated chambers used for a variety of industrial applications, including drying, curing, or baking components, parts or final products. Industrial ovens can be used for large or small volume applications, in batches or continuously with a conveyor line, and a variety of temperature ranges, sizes and configurations.

Process Window Index (PWI) is a statistical measure that quantifies the robustness of a manufacturing process, e.g. one which involves heating and cooling, known as a thermal process. In manufacturing industry, PWI values are used to calibrate the heating and cooling of soldering jobs while baked in a reflow oven.

Soldering station a multipurpose power soldering device for electronic components soldering

Soldering Station – multipurpose power soldering device designed for electronic components soldering. This type of equipment is mostly used in electronics and electrical engineering. Soldering station consists of one or more soldering tools connected to the main unit, which includes the controls, means of indication, and may be equipped with an electric transformer. Soldering stations may include some accessories – holders and stands, soldering tip cleaners, etc.

Thermal profiling

A thermal profile is a complex set of time-temperature data typically associated with the measurement of thermal temperatures in an oven. The thermal profile is often measured along a variety of dimensions such as slope, soak, time above liquidus (TAL), and peak.

Soldering process of joining metal pieces with heated filler metal

Soldering is a process in which two or more items are joined together by melting and putting a filler metal (solder) into the joint, the filler metal having a lower melting point than the adjoining metal. Unlike welding, soldering does not involve melting the work pieces. In brazing, the work piece metal also does not melt, but the filler metal is one that melts at a higher temperature than in soldering. In the past, nearly all solders contained lead, but environmental and health concerns have increasingly dictated use of lead-free alloys for electronics and plumbing purposes.

Conveyor belt furnace

A conveyor belt furnace is a furnace uses a conveyor or belt to carry process parts or material through the primary heating chamber for rapid thermal processing. It is designed for fast drying and curing of products and is nowadays widely used in the firing process of thick film and metallization process of solar cell manufacturing. Other names for conveyor belt furnace include metallization furnace, belt furnace, atmosphere furnace, infrared furnace and fast fire furnace, to just list a few.

A rising film or vertical long tube evaporator is a type of evaporator that is essentially a vertical shell and tube heat exchanger. The liquid being evaporated is fed from the bottom into long tubes and heated with steam condensing on the outside of the tube from the shell side. This is to produce steam and vapour within the tube bringing the liquid inside to a boil. The vapour produced then presses the liquid against the walls of the tubes and causes the ascending force of this liquid. As more vapour is formed, the centre of the tube will have a higher velocity which forces the remaining liquid against the tube wall forming a thin film which moves upwards. This phenomenon of the rising film gives the evaporator its name.