With the continuous innovation and advancement of semiconductor technology, the die bonding process of NTC thermistor chip is also constantly developing. At present, in order to meet the development needs of the industry, the die bonding process is gradually moving towards the direction of high integration, low power consumption and high reliability. EXSENSE Electronics Technology Co., Ltd. introduces some common die bonding process of thermistor chip so that everyone can fully understand it:
First, reflow soldering
The solder of this soldering process is generally solder paste, which is mainly soldered to NTC thermistor chip and substrate by reflow temperature curve. Generally, solder paste contains soldering flux, and some customers will apply additional soldering flux to help soldering according to the actual situation. The reflow soldering process can be soldered in air, nitrogen, and even in reducing atmospheres such as hydrogen, formic acid, etc. Since the part of the NTC chip including the semiconductor ceramic is composed of oxide, it is necessary to pay attention to the degree of damage to the NTC chip when soldering in a reducing atmosphere.
The reflow soldering process has high production efficiency and simple process, which is widely used in the electronic integration industry. Especially in the IGBT industry, it is still the mainstream die bonding process. Different customers have different reflow soldering processes, but the overall is still divided into three stages: preheating - soldering - cooling. When using the reflow soldering process, the following points need to be noted:
1. If the reflow soldering time is too long, it will easily lead to the electrode precipitation of the NTC thermistor chip, and its adverse performance is that the resistance value increases;
2. When the temperature rising/falling rate of the reflow soldering temperature curve is too fast, the strong temperature shock formed will cause the thermistor chip to crack, and its adverse performance is that the resistance value increases;
3. Too much solder paste will cause a bypass on the side of the NTC chip, and its adverse performance is that the resistance value decreases.
Second, silver glue/silver paste curing
This soldering process mainly combines the two main components inside the conductive silver glue/silver paste, the conductive filler (conductive particles) and the matrix resin, to form a conductive path to realize the conductive connection between the NTC thermistor chip and the substrate. Due to the conductive silver glue/silver paste mainly relies on the internal matrix resin for curing, its curing temperature will not be too high, and the common temperature is 100℃ and 150℃. When using the silver glue/silver paste curing process, the following points need to be noted:
1. Conductive silver glue/silver paste overflows too much on the side semiconductor ceramic of the thermistor chip will cause the resistance value decreases;
2. The epoxy resin in conductive silver glue/silver paste is a polymer material, high temperature will denature and deteriorate the NTC chip, resulting in increased resistance value drift.
Third, silver sintering
This soldering process mainly makes silver particles nanoscale and pressurizes them so that they are sintered at a lower temperature into a highly conductive solid. To ensure sintering compactness, a certain temperature and pressure are required, the general pressure is 15~20MPa, the temperature is generally 250~300℃, and the sintering atmosphere is mostly vacuum or nitrogen. Due to silver sintering requires greater pressure, the flatness and pressure resistance requirements of NTC thermistor chip is high.