![]() Convection rates are adjusted by setting the pressure in the heated air plenum in each zone. In a convection solder reflow oven convection is the dominant component of heat transfer. Modern reflow ovens used for mass production also have the ability to control convection rate – the speed at which the hot gases hit the product. Solder reflow ovens control the temperature profile by adjustments to the zone temperature set points and the belt speed. Controlling the Solder Reflow Oven Temperature Profile The reflow oven profile will be compared to solder specifications and board/component limitations including: ramp rates, peak temperature, TAL (time above liquidus) and other factors. ![]() time data can also be downloaded as a table and can be manipulated by MS Excel or other statistical programs. The measured reflow oven profile is often displayed visually, as a graph, but the raw temperature vs. The profiles can be measured in a loaded or unloaded state by either processing boards ahead of and behind the thermocoupled board to simulate the load or by sending the thermocouple board through alone for an unloaded test. The attached thermocouples can be measured by trailing the wires through the oven while processing or using a recording device that can be passed through the reflow oven by use of an insulating cover. Placing multiple thermocouples in differing locations and on different types of components on the board will give you the most comprehensive understanding of the thermal profile. ![]() Best practices for attaching thermocouples also suggest using strain relief to prevent the TC’s from being pulled off the board when the wires are tugged. Aluminum or Kapton tape can be used to attach thermocouples, but is not suggested due to trapped air and loosening of the tape’s adhesive. These thermocouples are attached using solder or epoxy. How to Profile a Solder Reflow OvenĪ solder reflow oven is profiled by attaching thermocouples (TC’s) to the board that is being processed. The difference between the reflow oven set points, or recipe, and the thermal profile is governed by the laws of heat transfer and is affected by mass (weight of the product), surface area, thickness, and the heat capacity (the ability of a material to absorb or give up heat). The temperature settings combined with the belt speed, and the convection rate settings, will produce the thermal profile on the board or product. The recipe is the temperature settings of the reflow oven in each zone. A thermal profile is a measurement of the temperature, of the product, during thermal processing. Subsequent blog posts will talk about other aspects of teh reflow profile.The thermal profile is an critical consideration in the solder reflow process. A recommended ramp rate would be between 0.75☌/s and 2☌/s. Heating the paste too much before all the solvents evaporate will cause the viscosity to decrease which will then lead to solder slumping. Another defect you may see from a too fast ramp-up is slumping of the solder paste, which can lead to bridging. It is crucial that this is a slow and controlled ramp-up if the paste is heated up too quickly the flux will boil and start to spatter solder all over the board. The very beginning of the reflow process, during the first few oven zones, focuses on drying out the solvents in the solder paste, getting ready for the activators in the flux to begin removing oxides. For this reason it is important to understand the different stages of a reflow profile and how they can affect the end solder joint. Often times solder defects such as spattering, voiding, slumping/bridging, and tombstoning can be remedied just by adjusting the reflow profile. SiP & Heterogeneous Integration & Assembly (HIA).The Indium Corporation & Macartney Family Foundation.
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