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In pcb board welding, wave soldering temperature curve

71 Published by FASTPCBA 8月 06,2019

In pcb board welding, wave soldering temperature curve

Temperature curve of wave soldering in pcb board welding

Temperature curve of wave soldering in pcb board welding

 

The entire pcb board welding process is divided into three temperature zones: preheating, welding and cooling. The actual welding temperature curve can be adjusted by programming the control system of the equipment.

wave soldering

wave soldering

In the preheating zone, the solvent in the flux sprayed on the pcb board is volatilized, which can reduce the gas generation during soldering. At the same time, the rosin and activator begin to decompose and activate, removing the oxide layer and other contaminants on the pcb soldering surface, and preventing the metal surface from re-oxidizing at high temperatures. The pcb board and components are fully preheated to avoid thermal stress damage caused by rapid temperature rise during soldering. The preheating temperature and time of the pcb board should be determined according to the size and thickness of the pcb board, the size and number of components, and the number of components mounted. The preheating temperature measured on the surface of the pcb board should be between 90 and 130 ° C. When there are more multi-layer boards or chip, the preheating temperature is taken as the upper limit. The preheating time is controlled by the speed of the conveyor belt.

 

The welding process is a complex process of interaction between metal, molten solder and air, etc. It is also necessary to control the soldering temperature and time. If the soldering temperature is low, the liquid solder has a large viscosity and cannot be well wetted and diffused on the metal surface, so that defects such as tipping, bridging, and rough surface of the solder joint are easily generated; if the soldering temperature is too high, the components are easily damaged.  And inactivate due to the carbonization of the flux, and the oxidation rate of the solder joints is accelerated, causing problems such as the solder joints being black and not full.

 

The peak surface temperature is measured and should generally be within the range of (250 ± 5) °C. Because heat and temperature are functions of time, the heat of solder joints and components increases with time at certain temperature. The welding time of the wave soldering can be controlled by adjusting the speed of the conveying system. The speed of the conveyor belt should be adjusted according to the factors such as the length of the wave soldering machine, the preheating temperature and the welding temperature. The welding time is expressed by the time when each solder joint contacts the wave soldering, and the welding time is generally about 3 to 4 seconds.

 

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