![]() 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. 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. They are usually situated as well from the top as from the bottom side. This profile is created by the temperature settings of the different convection zones. A conveyor will transport the PCB through a reflow oven where the PCB board is submitted to a reflow soldering profile. The solder paste needs to have enough adhesion force to keep the components in their place until soldering. In most cases, this is done with a Pick and Place machine. After solder paste application SMD components are placed on the solder paste with their solderable connections. Solder paste stability is hard to quantify but can be estimated from the stencil life indication in the technical datasheet. This is often referred to as the stability of the solder paste. 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. It also contains substances that will determine the consistency and the behavior of the solder paste in the process to a great extent. The gel flux contains substances to deoxydize the surfaces to be soldered. Dispensing and even more jetting also require finer grain sizes. Finer grains size are used for smaller pitch components and smaller stencil apertures. The solder powder is made of a certain soldering alloy and has a certain grain size (distribution). The type of gel flux and the type of powder and in what ratios they are mixed, will determine the consistency of the paste. Solder paste is a mixture of a solder powder and a gel flux. Depending on the application method the solder paste will have a different consistency and comes in a different packaging. ![]() ![]() The main application method is stencil printing but also dispensing and solder paste jetting are possible. This latter is called Pin in Paste (PiP) or intrusive reflow technology. 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. The reflow oven is usually a forced convection oven but also vapor phase and IR ovens are possible. 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 slow cooling can easily lead to an excess amount of intermetallic compounds and produce larger crystal particles together in soldering joint, reducing the fatigue strength.Reflow soldering is the most used soldering process in electronics assembly. Increase component’s fatigue risk –cooling down too slow.Components crack - cooling down too fastĬomponents experienced thermal shock outside of their specifications.Cooling zone (below 217~220☌ after reflow).The peak temperature should be 20~25☌ higher than the solder liquid point and remains there for 30~90 seconds. Cool solder - peak temperature is too low or time too short.Once the peak temperature is over 260☌ and stays there for more than 10 sec, most of components will be damaged. Component damaged – peak temperature is too high. ![]()
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