![]() ![]() Cooling zone: In the cooling zone, the temperature is gradually decreasing and makes solid solder joints.A common peak temperature is 20–40 ☌ above liquidus. Reflow zone: The reflow zone, also referred to as the “time above liquidus” (TAL), is the part of the process where the highest temperature is reached.Soaking zone: The preheating period from 150 ° C to the alloy molten point is also known as the soaking period, which means the flux is getting active and is removing the oxidized substitute on the metal surface so it is ready to make a good solder joint between components pins and PCB pads.It also lets big components heat up consistently with other small components. The benefit of the slow warm up is to let solvent and water in the paste vapour come out on time. The temperature ramp from normal to 150° C is less than 5° C /sec (at 1.5 ° C ~ 3 ° C / sec), and the time between 150° C to 180 ° C is around 60 ~ 220 sec. Preheating zone: Preheat usually refers to increasing the temperature from normal temperature to 150° C and from 150 ☌ to 180 C.There are four steps/zones to this process - preheating, soaking, reflow and cooling.įor the traditional trapezoidal type profile base on lead free solder paste that Bittele uses for SMT assembly process: Reflow soldering is a process by which the solder paste is heated and changes to a molten state in order to connect components pins and PCB pads together permanently. If using a reflow oven recipe generator check that it also considers the convection rate.Lead-free Reflow Profile: Soaking type vs. Many reflow ovens employ automated recipe generator software tools to facilitate the development of oven recipes. The pressure is adjusted by the control of the fan speed in each heated plenum. 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. The thermal profile is an critical consideration in the solder reflow process. ![]()
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