The biggest difference between reflow soldering and wave soldering

321 Published by FASTPCBA 7月 17,2019

The biggest difference between reflow soldering and wave soldering

The wave soldering craft is to fix the component to the corresponding position of the printed circuit board in advance via adhesive bonding mount component or the insertion hole of the printed circuit board and the positional movement won’t occur during the welding.

The condition of reflow soldering craft is different during welding. The solder paste is temporarily fixed at the corresponding position on the printed circuit board after the component being mounted. When the solder paste reaches the melting temperature, the solder “reflow” again. The position of the components shift due to the surface tension of the molten solder.

reflow soldering

If the pad design is correct (symmetrical pad position and size, appropriate pad spacing ), the solderability of the component terminal head and the printed circuit board pads are good, and all the solder terminals or pins of the component are simultaneously with the corresponding pads get wet by molten solder , it will produce self-alignment or self-correcting effect. If there is a small deviation in the mounting position of the component, it can be automatically pulled back to the target position under the action of surface tension. However, if the PCB pad design is incorrect, or poor solderability of the component terminals and the printed circuit board or the solder paste itself is of poor quality, or the craft parameters are not set properly, etc., even if the mounting position is exactly accurate, welding defects such as component positional deviation, suspension bridging, bridging connection, and poor wet welding may occur after welding process due to the unbalanced surface tension during reflow soldering .



Due to the features of “reflow” and “self-alignment effect” of the reflow soldering craft, which cause relatively loose mounting accuracy requirements, and high automation and high speed are relatively easy to realized. However, the reflow soldering craft has stricter requirements on pad design, component standardization, component terminal head and printed circuit board quality, solder quality and craft parameters at the same time.

The self-alignment effect has pretty large effect on the two terminal Chip components and BGA, CSP, etc., small amount of mounting shift can be corrected during reflow soldering. However, the self-alignment effect has relatively small effect on SOP, SOJ, QFP, PLCC and other components, and the mounting shift cannot be corrected by reflow soldering. Therefore, high-precision printing and mounting equipment are required for high-density, narrow-pitch SMD components. In addition, the self-alignment effect plays small role in lead-free welding.

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