![Mark5 1826 Reflow Oven](https://upload.wikimedia.org/wikipedia/commons/2/26/Mark5_1826_Reflow_Oven.jpg)
A reflow oven is a machine used primarily for
reflow soldering
Reflow soldering is a process in which a solder paste (a sticky mixture of powdered solder and flux) is used to temporarily attach one or thousands of tiny electrical components to their contact pads, after which the entire assembly is subject ...
of
surface mount
Surface-mount technology (SMT), originally called planar mounting, is a method in which the electrical components are mounted directly onto the surface of a printed circuit board (PCB). An electrical component mounted in this manner is referred ...
electronic components to
printed circuit board
A printed circuit board (PCB; also printed wiring board or PWB) is a medium used in Electrical engineering, electrical and electronic engineering to connect electronic components to one another in a controlled manner. It takes the form of a L ...
s (PCBs).
In commercial high-volume use, reflow ovens take the form of a long tunnel containing a
conveyor belt
A conveyor belt is the carrying medium of a belt conveyor system (often shortened to belt conveyor). A belt conveyor system is one of many types of conveyor systems. A belt conveyor system consists of two or more pulleys (sometimes referred to ...
along which PCBs travel. For prototyping or hobbyist use PCBs can be placed in a small oven with a door.
Commercial conveyorised reflow ovens contain multiple individually heated zones, which can be individually controlled for temperature. PCBs being processed travel through the oven and through each zone at a controlled rate. Technicians adjust the conveyor speed and zone temperatures to achieve a known time and temperature
profile
Profile or profiles may refer to:
Art, entertainment and media Music
* ''Profile'' (Jan Akkerman album), 1973
* ''Profile'' (Githead album), 2005
* ''Profile'' (Pat Donohue album), 2005
* ''Profile'' (Duke Pearson album), 1959
* '' ''Profi ...
. The profile in use may vary depending on the requirements of the PCBs being processed at the time.
Types of reflow ovens
Infrared and convection ovens
In
infrared
Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around ...
reflow ovens, the
heat
In thermodynamics, heat is defined as the form of energy crossing the boundary of a thermodynamic system by virtue of a temperature difference across the boundary. A thermodynamic system does not ''contain'' heat. Nevertheless, the term is al ...
source is normally ceramic infrared heaters above and below the conveyor, which transfer heat to the PCBs by means of
radiation
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:
* ''electromagnetic radiation'', such as radio waves, microwaves, infrared, visi ...
.
Convection ovens heat air in chambers, using that air to transfer heat to the PCBs by means of
convection
Convection is single or multiphase fluid flow that occurs spontaneously due to the combined effects of material property heterogeneity and body forces on a fluid, most commonly density and gravity (see buoyancy). When the cause of the convec ...
and
conduction
Conductor or conduction may refer to:
Music
* Conductor (music), a person who leads a musical ensemble, such as an orchestra.
* Conductor (album), ''Conductor'' (album), an album by indie rock band The Comas
* Conduction, a type of structured f ...
. They may be fan assisted to control the airflow within the oven. This indirect heating using air allows more accurate temperature control than directly heating PCBs by infrared radiation, as PCBs and components vary in infrared
absorptance Absorptance of the surface of a material is its effectiveness in absorbing radiant energy. It is the ratio of the absorbed to the incident radiant power. This should not be confused with absorbance and absorption coefficient.
Mathematical definitio ...
.
Ovens may use a combination of infrared radiative heating and convection heating, and would then be known as 'infrared convection' ovens.
Some ovens are designed to reflow PCBs in an oxygen-free atmosphere.
Nitrogen
Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
(N
2) is a common gas used for this purpose. This minimizes
oxidation
Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a d ...
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.
Vapour phase oven
The heating of the PCBs is sourced by thermal energy emitted by the
phase transition
In chemistry, thermodynamics, and other related fields, a phase transition (or phase change) is the physical process of transition between one state of a medium and another. Commonly the term is used to refer to changes among the basic states of ...
of a
heat transfer
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, ...
liquid (e. g.
PFPE) condensing on the PCBs. The liquid used is chosen with a desired
boiling point
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.
The boiling point of a liquid varies depending upon the surrounding envir ...
in mind to suit the solder alloy to be reflowed.
Some advantages of vapour phase soldering are:
* High energy efficiency due to the high heat transfer coefficient of vapour phase media
* Soldering is oxygen-free. There is no need for any protective gas (e.g.
nitrogen
Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
)
* No overheating of assemblies. The maximum temperature assemblies can reach is limited by the
boiling point
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.
The boiling point of a liquid varies depending upon the surrounding envir ...
of the medium.
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.
See also
*
Reflow soldering
Reflow soldering is a process in which a solder paste (a sticky mixture of powdered solder and flux) is used to temporarily attach one or thousands of tiny electrical components to their contact pads, after which the entire assembly is subject ...
*
Thermal profiling
A thermal profile is a complex set of time-temperature data typically associated with the measurement of thermal temperatures in an oven (ex: reflow oven). The thermal profile is often measured along a variety of dimensions such as slope, soak, ...
References and further reading
General references
*
Printed circuit board manufacturing
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