With the continuous enhancement of the function of electronic products, the integration of printed circuit boards is getting higher and higher, and the unit power of devices is also increasing, especially in communications, automobiles, rail transit, photovoltaics, military, aerospace and other fields, high-power transistors, RF power supplies, LEDs, IGBTs, MOSFETs and other devices are more and more used, and the packaging forms of these components are usually BGA, QFN, LGA, CSP, TO The common characteristics of packaging are high power consumption and high requirements for heat dissipation performance, and the void rate of heat dissipation pads will directly affect the reliability of the product. First of all, let's understand what are the characteristics of the furnace temperature curve of SMT vacuum reflow soldering machine
What are the characteristics of the furnace temperature curve of SMT vacuum reflow soldering machine?
01. Furnace temperature curve measurement method.
In the actual soldering process of vacuum reflow oven, the PCB board needs to stay in the vacuum area for about 10-30 seconds, so the temperature measurement process of vacuum reflow is different from that of traditional reflow ovens. There is a special temperature measurement mode in the equipment software, when the mode is started, when the temperature measuring plate reaches the vacuum area, the chain stops running as a whole, the upper cover of the vacuum chamber will not fall (avoid pressing the thermometer and temperature measurement line), the vacuum pump will not start, and the chain will resume operation after the residence time of the temperature measuring plate reaches the cumulative time set by the vacuum parameters, so as to complete the simulation test reflux curve.
In order to carry out the furnace temperature test more accurately, a special fixture can also be used, at this time, the vacuum chamber can be closed without using the temperature measurement mode, and the vacuum pump can be started for the actual testAt this time, it is necessary to consider the matching of the overall length of the thermometer and the temperature plate with the length of the vacuum chamber.
02. The reflux time is extended.
The PCB board needs to stay in the vacuum area for vacuum soldering, and the cycle time is generally about 30 seconds, and then it can continue to the cooling section, so the overall reflow time will be longer than that of ordinary reflow soldering, and its TAL time will reach about 100 seconds, the above figure shows a typical vacuum reflow oven temperature curve. Some components that are sensitive to reflow time pose a certain risk that needs to be avoided in process design.