What factors affect uneven heating of reflow soldering circuit boards

During the reflow soldering process, there may sometimes be uneven heating of components on the reflow soldering circuit board. JEENOCE divides the factors that affect the uneven heating of reflow soldering circuit boards into three aspects: the difference in heat capacity or heat absorption of reflow soldering components; Secondly, the edge of the conveyor belt or heater may have an impact; Thirdly, the load of reflow soldering products.

Firstly, PLCC and QFP typically have a larger heat capacity compared to a discrete sheet metal component, making it more difficult to weld large-area components than small ones.

Secondly, in the reflow soldering furnace, the conveyor belt not only performs reflow soldering on the conveyor products, but also becomes a heat dissipation system. In addition, the heat dissipation conditions at the edge and center of the heating part are different, and the temperature at the edge is generally lower. In addition to different temperature requirements in each temperature zone, the temperature on the same load surface also varies in the furnace.

Thirdly, the impact of different product loading capacities. The adjustment of the temperature curve for reflow soldering should consider achieving good repeatability under no-load, load, and different load factors. The load factor is defined as: LF=L/(L+S); Where L=length of assembled substrate, S=spacing of assembled substrate.

The greater the load factor, the more difficult it is to achieve good repeatability in reflow soldering process. The typical load factor range for reflow soldering furnaces is between 0.5 and 0.9. This depends on the product situation (component welding density, different substrates) and the different models of the reflow furnace. To achieve good welding results and repeatability, practical experience is crucial.