Vacuum brazing of electronic components

Vacuum Brazing of Electronic Components

Vacuum brazing of electronic components is a typical vacuum heat treatment application. For example, electronic components in satellites and aircraft must withstand extreme environments such as vacuum and extremely high temperatures. Manufacturing such reliable electronic components requires welding dissimilar materials together. Vacuum brazing joins different materials together, welding metal to metal and insulator to metal. The flux must be heat-resistant, suitable for the vacuum environment, and not allowed to vaporize. The main purpose of using flux is to remove residual oxides, reduce surface tension, and improve the wettability of the solder joint. However, exposure to vacuum or high temperatures can adversely affect the flux of electronic components. Flux materials containing acids and salts are prone to vaporization under high vapor pressure.

The production of components that withstand extreme environments requires specially designed furnaces that ensure the heat treatment process is carried out in a completely sealed vacuum environment. Depending on the sample materials and solder requirements, the furnace temperature needs to be adjusted to around 1200°C, requiring good temperature uniformity and stability. Data recording is also an important factor. For example, in the welding of dissimilar materials, an accurate temperature must be maintained before the filler transforms into a liquid state. Therefore, the furnace needs a controllable and repeatable data recording system.

Advantages of Vacuum Brazing

Because vacuum brazing materials have lower vapor pressures and are welded under vacuum conditions, it not only ensures higher weld quality but also expands the application range of vacuum brazing. It can weld highly oxidizing active metals (such as titanium and zirconium), light metals (such as aluminum), and refractory metals (such as tungsten, molybdenum, and tantalum). This is because these metals can completely avoid violent reactions with oxygen, water vapor, and nitrogen during welding under vacuum conditions, thus ensuring high-quality welds.

To meet the requirements of vacuum sealing and obtain leak-proof brazed welds, the following points should be followed:

(1) Use as little brazing alloy as possible. This results in a smaller, cleaner weld, which is better than a weld obtained with a large amount of brazing alloy.

(2) The gap between the weldments should not be wide or irregular.

(3) The minimum overlap between weldments must be at least 3 mm to allow capillary force to penetrate the brazing alloy.

(4) If brazing metals with different coefficients of thermal expansion, the brazing alloy must be compressed during the cooling process of the component.

(5) The weld structure controls the flow of the brazing alloy; the gaps at the corners determine how the brazing alloy will flow through those corners.

(6) To prevent the brazing alloy from flowing on the surface, a carbon or chromium coating must be applied to the surface.

(7) In brazing for vacuum sealing, lap joints and ladder joints are preferred.

Brazing Characteristics in Vacuum Furnaces

1. Operating Temperature: 300-1250℃ (depending on the brazing filler metal);

2. Vacuum Degree: 10⁻³~10⁻⁵ Pa;

3. Advantages: Oxidation-free brazing, can weld nickel-based high-temperature alloys, joint strength reaches over 90% of the base metal;

4. Typical Applications: Aero-engine blades, spacecraft heat pipes.