Why is the high-temperature sintering silver paste not bright enough for the sintered film?

Firstly, the organic matter in the sintered slurry is divided into two forms, one is organic solvents and various additives, which are discharged at a sintering temperature of 150 ℃~250 ℃. Another type is resin, which is discharged within 300 ℃~400 ℃, concentrated around 350 ℃, and completely discharged from the film layer within 400 ℃.

Slurry sintering furnaces are mainly divided into two categories: chain sintering furnaces and box type furnaces. General furnaces are more prone to problems. Mainly because the chain sintering furnace has a large space, generally at least four or five temperature zones, and some furnaces even have more than 10 temperature zones. This allows for better staged temperature setting, ensuring small temperature differences and good uniformity and stability of temperature. In addition, the feeding and discharging ports of the chain furnace are ventilated at both ends, and there is a dedicated exhaust pipe in the front temperature zone. Organic matter can be smoothly discharged at low temperatures, ensuring a clean atmosphere inside the furnace. But for box type furnaces, the conditions will be worse. The furnace cavity is relatively small, and some do not have exhaust holes, which can cause organic matter in the slurry to be discharged and remain in the furnace during sintering. As the temperature increases, these organic matter will carbonize and adhere to the surface of the sintered film, forming a carbonized film that is not bright enough and turns dark yellow.

In terms of heating, some are pre embedded heating wires, while others are rod-shaped heating wires such as silicon carbide. This can cause the temperature around the heating rod to be much higher than the temperature in the middle of the furnace, usually several tens of degrees higher, and even up to about Baidu. When the heating wire temperature is highest, the temperature inside the furnace will be higher in the deepest part, and the temperature at the furnace entrance will be lower. Only the temperature in the middle part of the furnace is relatively uniform and close to the set value. The difference in temperature between different parts of the furnace body results in significant color differences for some products from the same batch after firing. For silver paste, there may be a yin-yang face, and even some parts of the same film layer may be overheated and melted into silver beads, while others may not be fully sintered. For resistors, it is manifested in the lack of consistency in resistance values (due to inconsistent resistance paste, fine printing processes, and equipment accuracy factors).

How should a box furnace be sintered?

Firstly, according to the emission pattern of organic matter, bake in the oven at 150-200 ℃ for 10-20 minutes before putting it into the furnace, allowing the organic matter to be discharged once.

Secondly, when placing the baked sintered pieces in the furnace, ① they should be placed at a suitable distance from the heating wire ② they should be placed at a suitable distance from the inside of the furnace body ③ they should not be too close to the furnace door, and should be placed slightly inward. ④ Do not place too many items inside the sintering furnace at once.

Thirdly, after baking, put it into the furnace and heat it up with the furnace. At the stage of 300-350 ℃, open the furnace door slightly to allow organic matter to be smoothly discharged from the furnace. Afterwards, close the furnace door, heat up to the peak with the furnace, keep it warm, and then cool down with the furnace.