The briefly introduction to reflow soldering

Reflow soldering by remelting the paste solder pre-distributed on the printed board pads to realize the mechanical connection and electrical connections between the solder ends or pins of surface mount components and the printed board pads.

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1. Classification of reflow soldering

(1). Can be divided into two categories by the heating area of reflow soldering : heating the whole PCB ; heating the part of PCB.

(2). The overall heating and reflow welding of the PCB can be divided into: hot plate reflow welding, infrared reflow welding, hot air reflow welding, hot air plus infrared reflow welding, and gas phase reflow welding.

(3). Local heating and reflow soldering of PCB can be divided into:Laser reflow welding, focused infrared reflow welding, beam reflow welding, hot air reflow welding.

2. Features of reflow soldering

Comparing with wave soldering technology,the reflow soldering’s features as below:

(1). The thermal shock to the components is small;

(2). It can control the amount of solder paste;

(3). Self-alignment effect-When the component placement position is deviated, due to the surface tension of the molten solder, when all the solder ends or pins and the corresponding pads are wetted at the same time, the surface tension acts, components automatically can be pulled back to the approximate target position;

(4). No impurities will be mixed into the solder, and the composition of the solder can be correctly guaranteed;

(5). Can be welded on the same board with different welding processes; 

(6).  Simple process and high welding quality.

3.Advantages of reflow soldering 

(1). The solder paste can be distributed quantitatively, with high precision, less times of heating of the solder, not easy to be mixed with impurities and less pairs. 

(2). Suitable for welding various high-precision, high-demand components, such as 0603 resistors and capacitors, and QFP, BGA and CSP and other chip package devices. 

(3). There are few welding defects, and the rate of defective solder joints is less than 10 * 10-6. Nowadays, with the acceleration of the use of lead-free solder and the increase in solder prices, the original advantage of wave soldering is gradually lost, and more electronic products will use the reflow soldering process.

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