Irrelevant of the chip range and size you are utilising on the board, you may still find that the board consists of voiding in some of the solder joints. Ensuring the boards achieve sufficient wetting, especially when they are densely populated, can be a challenge - often with a diverse range of component sizes, ranging from anywhere between 0201 to 2920 chips sizes, all with a different thermal mass. One of the potential consequences can be the insufficient wetting of the boards. If you start adjusting the temperature of one of the zones, it will adjust the other zones to compensate, which could lead to undesirable consequences. The conveyor belt is key to driving the boards through the system, and adjusting the speed of the belt can help to refine the reflow process without having to manipulate the temperature of the different zones. However, some convection ovens consist of additional reflow zones and one advantage of additional heating zones is it gives you greater process control.Īs the convection process is ‘in line’ with the rest of the assembly process, greater throughput can be achieved because it integrates with the other SMT systems, automating the entire process. These phases are depicted as zones within the convection oven, where the PCB passes through on a conveyor belt. Typically, the convection method consists of four heat phases: preheat, thermal soak, reflow and cooling. These consist of variables such as the type of solder utilised, ie, no-clean and water-soluble lead-free solder, the manufacturer of the solder paste, stencil design, as well as the reflow process used - convection and vapour phase reflow. For some engineers, filling the void and ensuring there is sufficient solder around the solder joint becomes a balancing act of several factors. One consideration is the minimisation of voids. In this article we look at both technologies and compare the advantages and disadvantages with the aim of helping you to make an informed decision, if you are looking to invest in a solution. Two of the main technologies deployed on the shop floor are based on either convection or vapour phase technology. The reflow process has taken on a life of its own with the evolution of changes in technology, impacted by environmental factors and the demand for greater accuracy with tighter tolerances. Like we have discussed in the previous two articles, each process comes with its own set of challenges and the reflow stage is no exception. One of the last steps in the PCB production process, following the screen printing and component placement, is reflow.
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