Ningbo electronic processing chip processing _PCB bonding _ _ Midland SMT SMT Rework for success helps when two of the most critical processes, but also two of the most prone to ignore the problem: Because these two fundamental processes often rework staff ignored, in fact, sometimes worse than the situation after the repair before the repair. Although some "repair" defects can sometimes be after the procedure inspector found, but in most cases do not always see it, but immediately after the circuit tests will be exposed. Preheat - Successful repair of the premise is true, PCB long period of time at a high temperature (315-426 ℃) under the process will bring a lot of potential problems. Heat damage, such as pads and leads warping, board delamination, raw white or blistering, discoloration. Alice and burned board usually cause inspectors attention. However, it is because it would not "burn out board" does not mean to say "board is not damaged." High temperature on the PCB's "invisible" damage is even more serious than the issues listed above. For decades, numerous tests repeatedly proved PCB and its components can "pass" reworked inspection and test, the decay rate is higher than normal PCB boards. This substrate warpage and its internal circuit elements decay and other "invisible" issue from different materials with different coefficients of expansion. Obviously, these problems do not self-exposure, even at the start of the circuit test went undetected, but still lurking in the PCB assembly. Although the "rework" looked after very well, but as is often said of the sentence: "The operation was successful, can be patient unfortunately died." When heat causes tremendous stress, room temperature (21 ℃) of PCB assemblies sudden contact with heat to about 370 ℃ of the soldering iron, desoldering tools or heat limelight local heating of the board and its components is about 349 ℃ of temperature difference changes, resulting in "popcorn" phenomenon. "Popcorn" phenomenon is present in an integrated circuit or SMD in the device's internal moisture rapidly heated in the repair process, the moisture expansion of micro-burst or rupture occurs phenomenon. Therefore, the semiconductor industry and circuit board manufacturing requires production personnel prior to reflow, to shorten the warm-up time, the rapid rise reflow temperature. In fact PCB assembly reflow process has been included in the preheating stage before the reflow. Whether PCB assembly plants is the use of wave soldering, vapor phase or infrared convection reflow soldering, each method generally is preheated or the heat treatment temperature is generally in the 140-160 ℃. Before the implementation of reflow, using a simple short-term preheat PCB rework many of the problems can be solved when. This reflow process for several years of successful history. Therefore, the benefits of PCB components before reflow preheating is multifaceted. Information Reference: www.mdlsmt.com/qydt.html