Adhesive Remover Wipes
Suitable for
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Reflow soldering is the most used soldering process in electronics assembly. Mainly SMD (Surface Mount Device) components but also some through hole components are soldered in a reflow oven to a PCB (Printed Circuit Board) by means of a solder paste. The reflow oven is usually a forced convection oven but also vapor phase and IR ovens are possible. The first step of the process is to apply solder paste to the pads of the PCB or in case of through hole components in the through hole. This latter is called Pin in Paste (PiP) or intrusive reflow technology. The main application method is stencil printing but also dispensing and solder paste jetting are possible. Depending on the application method the solder paste will have a different consistency and comes in a different packaging. Solder paste is a mixture of a solder powder and a gel flux. The type of gel flux and the type of powder and in what ratios they are mixed, will determine the consistency of the paste. The solder powder is made of a certain soldering alloy and has a certain grain size (distribution). Finer grains size are used for smaller pitch components and smaller stencil apertures. Dispensing and even more jetting also require finer grain sizes. The gel flux contains substances to deoxydize the surfaces to be soldered. It also contains substances that will determine the consistency and the behavior of the solder paste in the process to a great extent. When stencil printing solder paste, an important parameter is that the solder paste keeps its printing properties during the time it will be on the stencil. This is often referred to as the stability of the solder paste. Solder paste stability is hard to quantify but can be estimated from the stencil life indication in the technical datasheet. After solder paste application SMD components are placed on the solder paste with their solderable connections. In most cases, this is done with a Pick and Place machine. The solder paste needs to have enough adhesion force to keep the components in their place until soldering. A conveyor will transport the PCB through a reflow oven where the PCB board is submitted to a reflow soldering profile. This profile is created by the temperature settings of the different convection zones. They are usually situated as well from the top as from the bottom side. Beside the temperature settings, in some cases also the convection rate of the zones can be programmed to get better or lower heat transfer, or when some high components experience too much force from the convection. It is the goal to get all components to soldering temperatures, which is determined by the used soldering alloy, without damaging or overheating temperature sensitive components. This can be a challenge for units with a large diversity of big and small components or an uneven Cu-distribution in the PCB board. In that perspective a low melting point soldering alloy substantially limits the risk of damaging or predamaging components and PCB boards. The speed of the conveyor will determine the time of the profile and the throughput of the oven. In most cases however the Pick and Place process is limiting the throughput. Not all electronic components are suitable for reflow soldering. Some because of their thermal mass like e.g. big transfos or others because of their thermal sensitivity like e.g. some displays, connectors, relays, fuses,... These components are usually available as a through hole components and soldered in other processes like selective soldering, wave soldering, hand soldering, robot soldering, laser soldering,...