In order to get the best profile, temperature rising rate is recommended to be 0.5~1?/second for traditional profile, it is better to use a rate of 3~4?/second. Temperature rising rate during preheating stage: In terms of heating stage, low temperature rising rate from room temperature to melting point is expected to reduce most of the defects. Generally, 80~160? preheat stage takes 60 ~120 seconds, thus effectively removing the volatile solvent in solder paste, reducing the thermal shock for component, getting flux fully activated and temperature difference smaller. Preheat time: It depends on the component with highest heat capacity, PCB area, PCB thickness and performance of solder paste used. If preheat temperature is too low, flux may not be activated fully. Please see attached figure for the relationship between copper plate temperature and oxidation speed). In high-temperature zone, oxidation speed may increase in a linear way if it is preheated to about 150?, oxidation rate may be several times of that in room temperature. Please note that high temperature results in much faster oxidation. For traditional profile, constant temperature zone lies between 140~160?. Generally, it is set at 80~160? and temperature should rise slowly (to get the best profile). Preheat temperature: Temperature is set according to what solder paste is used and what conditions are recommended by manufacturers. Preheating: Preheating refers to heating which is to activate the flux and avoid any defect due to rapid heating when component is soldered. Profiles’ general technical requirements for each stage,In general, profile can be divided into three stages: Preheating, reflow soldering and cooling. Two - Reflow profiles’ general technical requirements and main formsġ. Therefore, appropriate design of profile can result in higher yield and reliability and reasonable control of profile has a pivotal role in soldering process. Defects caused by inappropriate profile mainly include cracks, warped components, tin sweats, bridging, Pseudo soldering, cold soldering, PCB delamination or blister, etc. Thus, profile is an important factor to decide soldering defects. The form of reflow soldering process mainly is the profile, referring to the curve of temperature change over time which is tested on SMT component. If there is no reasonable and feasible reflow soldering process, any process control before said makes no sense. The purposes of all process controls during surface mounting are to realize high soldering quality. Defects caused by improper design of surface-mount PCBs, solder paste printing and component mounting will eventually find expression in soldered products. Reflow soldering is a main method to form solder joints on SMT base-panels and so is a core technology in SMT process. One - Profile’s importance in reflow soldering
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