《How to use SMT Line to produce a printed circuit board? (5)》
When the small volume components such like capacitors, resistors and large volume such as BGA or connector has been placed on the circuit board by high-speed and general speed pick and place machine. The next critical step for the SMT( Surface Mount Technology) is reflowing to melt the solder paste. The temperature of the reflow will affect the final quality of the surface mount. Usually the melting point is about 217°C. and the maximum temperature should not exceed 250°C, otherwise the components will be melting and out of shape.
The temperature profile is the key to the reflow phase success. It has four different zones in temperature profile: pre-heat zone, soak zone, reflow zone, and cooling zone. Pre-heat zone usually increase the temperature slowly from normal to 150°C. And then the temperature increasing gradually to 190°C in soak zone. The reflow zone will be the highest temperature in entire zone. Ideally all the components should keep in same temperature and speed rate to ensure the reflow phase complete successfully. Finally that the product start to cooling. Generally, the maximum cooling rate is around 4 ° C / min. After that the whole PCB assembling process is done.
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Reflow Profile :- The reflow temperature profile is defined by the relationship of temperature versus time during heating. ... <看更多>