Reflow Ovens Information
Reflow ovens are electronic heating devices used to mount electronic components to printed circuit boards (PCB) using surface mount technology (SMT). The electronics manufacturing industry maintains SMT as an industry standard due to the advantage it offers of simpler construction of electronic devices. Reflow ovens vary in size and type. Commercial reflow ovens range in cost from thousands to tens of thousands of dollars. The option to construct homemade reflow ovens reduces costs; however it limits both functionality and durability.
The invention of the reflow oven solved the problem of excessive time consumption involved in manually soldering most surface mount technology (SMT) components. As a result of technological limitations, when first introduced, the evolution of reflow ovens reflects the need to operate as efficiently as possible with the equipment available at that point in time. This process led to the development of the low mass convection reflow ovens preferred today. These modern reflow ovens allow for shorter profiles and more consistent, even heating compared to earlier models.
There are several types of reflow ovens. All types are instrumental in ensuring the proper mounting of electrical components and securing circuit board connections via reflow soldering techniques. Individual zones control the temperatures of infrared and convection reflow ovens. A variety of heating and cooling sub-zones exist within each zone.
Vapor phase ovens use thermal energy to heat the PCB. Tasks requiring fast heating and cooling use an industrial built reflow oven. The increased strength of the completed product results through a rapid heating process that places less thermal stress on the modules.
Reflow ovens vary in size, type of heating and features. However, the most common types of reflow ovens are:
- Batch reflow ovens
- Bench top reflow ovens
- In-line conveyor reflow oven
Heating solder alloy softens the material. The term “reflow” refers to the temperature necessary to melt a solid mass. Solder does not flow until the reflow temperature is reached. A reflow oven enables control of the temperature as solder and PCB components combine with soldering paste. Solder flow takes place more than once automatically compared to modern circuit assembly techniques that incorporate reflow soldering.
Today’s reflow ovens have a variety of features matched to the type of production intended for use, the duration of production and the desired outcome. One of the key features of reflow ovens is preheating which is the range from room temperature to the melting point of solder.
The most common features and specifications include:
- Thermal performance
- Maximum temperature rating
- Heating technology
- Reflow oven type
- Entrance clearance
- Maximum PCB width and height
- Speed of conveyor
- Computer software and PC interface
- Power supply
Maintenance downtime required
Reflow soldering is the usual way of attaching a surface mount solder to a circuit board. However, it is also used for through-hole components (THT) by filling all holes with solder paste and running the component leads through the paste. A reflow oven is inappropriate for use on pure through-hole boards due to simpler and less expensive characteristics of wave soldering. However, a reflow oven helps to reduce the assembly costs of boards containing a mix of both through-hole boards and surface mount boards. It aids in the protection of electrical components, removing the potential for damage caused by overheating during the soldering process.
Selecting Reflow Ovens
Selecting a reflow oven requires special consideration of all aspects that affect the process of production. Contemplate the products required for production, desired production levels, time frames and strength requirements of the bond.
Choose a reflow oven centered on the following criteria:
- Thermal vs. shock sensitive components
- Heating profiles
- Range of temperatures required for heating robust materials
- Heating processes that deliver best results with particular components
- Intended use of large or heavy pieces
It holds true that household appliances make optional reflow ovens, such as toasters or microwave ovens that use infrared rays as the source of heat. However, drawbacks of this method include the inability to set up a proper profile or establish cooling methods. Homemade reflow ovens satisfy simple, smaller jobs and are not adequate for ongoing, larger projects.
Thermal profiling establishes techniques that prevent defects in the final product. The term describes the act of measuring multiple points on a circuit board to determine the ideal rate of heating and cooling. The measurement of thermal temperatures inside an oven includes a complex set of time and temperature data. This data defines profiles referred to as ramp-soak-spike or ramp-to-spike. Ramp, soak and spike suggest the temperatures needed to change the structure of solder and the time it takes to occur.
Weaker joints form as a result of improper profiling. Inadequate temperature settings damage components by the rate of heating and cooling. Ensure proper reflow oven profiling to avoid costly production problems.
Further Reading on Reflow Oven Requirements
A reflow oven is the ideal choice for several soldering needs. Meet optimum results by identifying all aspects of the product characteristics including component types, solder and board requirements, volume, pace, size and thermal necessities.
To help in choosing the reflow oven that appropriately meets your needs, research the specifications noted in the IPC/EIA J-STD-001 Requirements for Soldered Electrical and Electronic Assemblies document. The documentation is available on manufacturer websites or provided by certified suppliers.
IPC-7801 - Reflow oven process control standard