Solder reflow temperature1/27/2024 ![]() ![]() The next stage is called thermal soak zone and consists of exposing the assembly to a constant temperature and for a duration of 1 to 2 minutes, allowing to complete the elimination of volatiles from the solder paste by evaporation, will activate the fluxes such as PCB flux, the components will begin to adhere to the pads of the printed circuit board and allow the adhesion free of oxide to be performed by being involved in an environment of evaporated fluxes. This heating process requires strict control so that the required temperatures can be reached for the solder to achieve a strong and consistent connection to the printed circuit board, but that these temperatures also do not reach dangerous levels for the semiconductor material of the components as they could damage them. The heating process within this oven is separated into several stages and the way in which the heat is applied and its control of temperature increase over time is a critical factor in order for the components to adhere properly, to have a quality finish soldering and to avoid damage to the internal circuitry of the PCB components. The printed circuit board is taken to a reflow machine where the soldering process as such will take place. This process can also be carried out manually, when the project is small or has very few SMT surface mount components, using tweezers each component can be placed on top of the corresponding pads, as the solder paste is a creamy texture it will allow to hold the components slightly because of a physical phenomenon known as surface tension. This task is carried out by the pick and place machine which is an automated machine that will accurately place each component in the right place. The next stage is to place the electronic components on top of the PCB in the exact correct location so that each terminal of each component matches the corresponding pad on the PCB. The PCB will then have a small amount of solder paste on each of the pads where a surface mount or SMT component will be located. This perforation pattern is obtained from the StopMask layer of the Gerber files generated during the PCB design stage. To apply this solder paste on these pads a sheet known as a “stencil” is used which will serve as a template in the application of the solder paste, this stencil is usually constructed in a thin sheet of metal with perforations that match the pads of the printed circuit board. Solder paste can have a texture similar to toothpaste with the characteristic color of solder used in electronics. ![]() The solder paste used in the reflow soldering method consists of small spheres of solder metal (or the alloys used in it silver, tin, lead etc) combined with solvent pastes and agents that help the adhesion of the components such as flux keeping the small solder spheres in suspension. These pads are uncovered from the StopMask layer because solder will be applied to these pads. In SMT assembly, surface mount assembly requires that the printed circuit boards have pads on which the electronic components will be soldered. Now let’s look at the process in more detail so that you can understand how this soldering method works. Let’s get into the subject of reflow soldering, in a nutshell, this consists of applying a layer of solder paste on the pads of the printed circuit board, then place the SMD components in the correct position, the printed circuit board will be taken to an oven which will heat the entire assembly allowing the solder to melt and then solidify fixing all components electrically and mechanically to the printed circuit board. In this article, we will refer to reflow soldering, a type of soldering which is mostly used in the industrial field, although nowadays there are some small reflow soldering devices that can be purchased by the amateur and used in the small workshop of the electronics hobbyist. There are numerous soldering methods ( wave soldering, reflow soldering, manual soldering and more), some used in the industrial field, others in the amateur and hobbyist environment and some techniques are used in both fields. Then this welding must provide a union of electrical conduction, which is a union of electromechanical characteristics that will allow the components are fixed together to a chassis structure or a printed circuit board and at the same time can be electrically connected to the terminals of this or pads as appropriate, in a reflow oven the union is usually terminals or wires and in the case of printed circuit boards are pads. Soldering is a method generally of thermal nature (this means that it uses heat at temperatures much higher than those of the environment), by means of which two or more components can be joined mechanically and in the case of areas related to electronics the electrical connection of electronic components.
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