Introduction to reflow soldering process
From: Author:Mark Hardy Publish time:2021-09-08 11:53 Clicks:0
Introduction to reflow oven
The flow furnace process is to remelt the paste-like solder pre-distributed on the printed board pad to realize the mechanical and electrical connection between the solder end of the surface mount component or the pin and the printed board pad. . The reflow oven is the last key process of SMT (Surface Mount Technology). It is a real-time process control. The process changes are more complicated and involve many process parameters. Among them, the setting of the temperature curve is the most important and directly determines the quality of reflow soldering.
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■ Corresponding to high-performance welding requirements
■ Oxygen-free environment for preheating and welding process
■ Temperature consistency of the entire welding assembly
■ Overheating will never happen
■ No shadow phenomenon
■ Single board can be welded multiple times
■ Ultra-low operating cost
■ Flexible versatility and independent operation
Principle of hot air reflow in reflow oven
When the PCB enters the preheating zone, the moisture and gas in the solder paste evaporate, the flux wets the component pins and pads, and the solder paste begins to soften and cover the pads to isolate the component pins and pads from oxygen; PCB enters In the reflow zone, the temperature rises rapidly, and the solder paste reaches a molten state, wets, diffuses, reflows, and then cools the component pins and pads on the PCB to form a solder joint, thereby completing the reflow soldering.
Forced convective hot air reflows through air circulation. The upper and lower surfaces of the components produce high-efficiency heat transfer at a relatively low temperature. At the same time, small components can avoid overheating and avoid PCB deformation due to single-sided heating. The solder joints are heated relatively uniformly, thereby achieving reflow soldering.
Reflow oven temperature setting steps
1) First of all, set the conveyor belt speed according to the production volume. Pay attention that the belt speed cannot exceed the maximum speed allowed by the reflow welding process (here it means that the preheating temperature rise rate should be ≤3℃/s, and the peak welding temperature and reflow time should meet Welding requirements).
2) Set the furnace temperature for the first time.
3) After ensuring that the temperature in the furnace is stable, perform the first temperature curve test.
4) Analyze the difference between the measured temperature curve and the designed temperature curve, and perform the next furnace temperature adjustment.
5) After ensuring that the temperature in the furnace is stable and the test SMA is cooled to room temperature, perform the next temperature curve test.
6) Repeat the process of 4) to 5) until the measured temperature curve is consistent with the designed ideal temperature curve.
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