Reflow soldering: An introduction to the technology and applications
Reflow soldering, also known as reflow soldering, is a high-precision soldering process that is widely used in electronics production. Electronic components are soldered onto a circuit board by controlled heating and subsequent cooling. This process aims to create reliable and efficient soldered connections. Here we take a look at how this process works and the potential risks and how to avoid them.
The steps of the reflow soldering process
Paste application
At the beginning Solder paste is applied to the circuit board. This paste serves as a medium for connecting the components to the PCB.
Component placement
Electronic components, such as chips or SMD components, are placed precisely on the areas of the PCB coated with solder paste in accordance with the specifications of the placement plan.
Heating in a reflow oven
The PCB is transported into the reflow oven on a conveyor belt and passes through five heating zones. There it is exposed to an individual soldering profile. This profile consists of different phases and depends on various factors, such as the thickness of the PCB, the solder paste used and the sensitivity of the components.
To optimize the quality of soldering and prevent oxidation, a protective atmosphere can be created by adding nitrogen. If the concentration of nitrogen falls below the specified limit value, the PCB is not fed into the oven. This limit value is monitored during the entire process in the oven.
Reflow-Phase
During this phase, the solder paste melts on the surfaces of the components and the PCB. The components are aligned in their predefined positions using surface tension and capillary forces and simultaneously connected to the conductor tracks. This process takes place in three adjustable soldering zones.
Cooling down
After the reflow process, the PCB is cooled in a controlled manner in three cooling zones. This creates a solid solder connection between the components and the PCB.
EXAMPLE OF A SOLDERING PROFILE
RISKS ASSOCIATED WITH REFLOW SOLDERING AND HOW TO AVOID THEM
WRONG SOLDERING PROFILE
Incorrect adjustment of the soldering profile can lead to incomplete soldered joints or even damage to components. Careful monitoring and adjustment of the soldering profile are crucial to avoid undesirable consequences.
COMPONENT DAMAGE
High temperatures during the soldering process can damage sensitive components. This can lead to cracks in components, for example.
Soldering paste
Each solder paste has different properties that must be matched to the product to be soldered. An incorrectly selected solder paste can have a negative impact on the soldering quality.
OXIDATION
DThe increased temperatures in the reflow oven promote oxidation on the PCB and components, which can prevent the formation of high-quality solder joints. The use of nitrogen and flux in the solder paste prevents this.
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