What Is a Reflow Soldering Carrier Board?
2024-08-26 17:29
An SMT reflow soldering carrier board, by definition, is a tool used to hold a PCB (Printed Circuit Board) before the PCB is placed into a reflow oven. Typically, a reflow soldering carrier board is equipped with positioning pins, which serve to secure the PCB and prevent it from shifting or warping.
Some advanced reflow soldering carrier boards come with a cover—this design is generally used for FPCs (Flexible Printed Circuits). Magnets are installed on these carrier boards, and during the loading process, suction cups are used for fixation. This setup can more precisely prevent the board from warping. Additionally, covers are also used for some rigid PCBs, as they help secure certain components and prevent them from sliding during the reflow soldering process.
What Are the Uses of SMT Reflow Soldering Carrier Boards?
1. Reducing PCB Warping
No matter how well a reflow soldering carrier board is designed, PCBs will inevitably experience some degree of warping after high-temperature soldering—this is acceptable as long as the warping does not affect product quality. To minimize warping, reflow soldering carrier boards are designed with positioning pins to secure the PCB, and additional support rods are also integrated to provide auxiliary support for the PCB.
2. Preventing Heavy Components from Falling Off
Reflow soldering carriers can be custom-designed to hold specific components that tend to fall off during the second-side soldering process (after the first side has been soldered). These components are usually heavy ones, such as network cable connectors.
Both of the above functions are closely related to the high-temperature zone of SMT reflow ovens. Currently, most products adopt lead-free processes: the melting temperature of lead-free SAC305 solder paste is 217°C, while that of SAC0307 solder paste ranges from 217°C to 225°C. Generally, the maximum recommended temperature for reflow soldering is between 240°C and 250°C.
However, for cost considerations, FR4 circuit boards with a glass transition temperature (Tg) of 150°C or higher are typically selected. Additionally, PCBs are becoming increasingly thinner—with thicknesses reduced from the conventional 1.6mm to 0.8mm, or even 0.4mm. Such thin PCBs are more susceptible to warping when exposed to the high temperatures of SMT reflow soldering.
In essence, SMT reflow soldering carrier boards are developed to address the issues of PCB warping and component falling. They usually use positioning pins to fix the PCB via its positioning holes, effectively maintaining the PCB’s shape to reduce warping when the board material deforms under high temperatures. Moreover, additional reinforcement structures are essential to prevent the middle part of the PCB from bending and sagging due to gravity.
Furthermore, leveraging the non-deformable property of carriers, they can support heavy components to ensure these components do not fall off. However, the design of reflow soldering carriers must be extremely careful—excessive support points should be avoided, as they may lift components and cause inaccurate solder paste printing on the second side of the PCB.
What Characteristics Should an Ideal SMT Reflow Soldering Carrier Have?
1.Softening and deformation temperature above 300°C: It must be reusable without deformation, which is the primary requirement.
2.Low thermal expansion: Thermal expansion and contraction are inherent properties of most materials. If a reflow carrier has excessive thermal expansion, it will damage the PCB.
3.Easy-to-process and lightweight material: Since reflow carriers need to be handled (picked up and placed) by operators, heavy carriers are unsuitable for general electronic factory operations.
4.Low heat absorption or fast heat dissipation: Reflow carriers are used repeatedly. If the carrier cannot cool down to a temperature manageable by human hands after reflow soldering, additional carriers must be prepared, which increases costs.
5.Cost-effective and suitable for mass production: The material should be as affordable as possible to enable large-scale manufacturing.
6.Common materials for reflow carriers: Aluminum alloy is widely used. In addition, reflow carriers are often made of high-carbon steel or magnesium alloy. Although aluminum alloy is lighter than ordinary ferrous metals, it still has a certain weight.
Moreover, aluminum alloy tends to absorb heat—after being removed from the oven, operators must wear heat-insulating gloves or wait for a period of time for it to cool down before handling, which makes operation somewhat inconvenient. There is also a type of dedicated reflow carrier made of a more economical material, but it has a shorter service life. Recently, some reports have indicated that this material may cause allergic reactions.
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