3/10/2024 0 Comments Lead free solder reflow profileIt becomes apparent that conveyor speed has an immensely complex influence on the reflow profile, eliciting the question: “Can tin/lead (SnPb) and tin/silver/copper (SAC) soldering processes be implemented in the same temperature zones simply by using two different conveyor speeds?” longer dwell time in the oven), all reflow times (preheating time, time above liquidus, and cooling time) increase, maximum temperatures rise, and the difference in temperature between small and large thermal masses on the PCB is increased. As shown in Figure 1, as conveyor speed is reduced (i.e. In other words, changing the conveyor speed inevitably alters the temperature profile for the PCB. Therefore, differing conveyor speeds with constant temperature differences (oven zone temperature minus PCB temperature) must result in different amounts of heat flow within the PCB. The amount of time specified in the equation is determined by the speed at which the PCBs move through the system. Influence of conveyor speed on the reflow profile. Thermodynamic CharacteristicsHeat transfer between a reflow system and the PCB to be soldered is generally described by means of: q = α × t × A × Δ T, where α = heat transfer coefficient W/m2K t = time in seconds A = surface area in square meters and ΔT = temperature difference (K).įigure 1. In this case, investment costs are only increased by the amount required for a two-lane conveyor system. This is accomplished by taking advantage of the thermodynamic characteristics of the heat transfer system. The other alternative is that different reflow profiles can be set up next to each other within a thermal system for two conveyor lanes. This adds significant cost to the reflow equipment. Stated briefly, this involves the use of two ovens in one. in addition to the conveyor lanes, there are two separately controllable heating systems for reflow profiling. Manufacturers can set up two thermal systems next to each other within one basic system i.e. Implementing both processes simultaneously with a single reflow soldering system is an inexpensive alternative.įrom a technical standpoint, implementing both processes simultaneously with a single reflow soldering system can be approached in two ways. The separate SMD production lines this demands, or the continuous changing of process parameters to match the respective solder at a single production line, can increase manufacturing costs. Meanwhile, a few temporary exceptions to the ban on lead are forcing many electronics manufacturers to work with tin/lead as well as lead-free solders. Implementing both processes simultaneously with a single reflow soldering system can be approached with leaded and lead-free reflow profiles set up next to each other within a thermal system with two conveyor lanes.īans on the use of hazardous substances, set forth by RoHS, have become daily routine in manufacturing facilities around the world. With many electronics manufacturers still running leaded and lead-free assembly jobs, reflow ovens are tasked to run both solder-type profiles.
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