Tungsten Wire For Vacuum Metallizing

Tungsten wires or filaments are commonly used in vacuum coating as evaporation source materials. Due to their high melting point, low vapor pressure and good thermal stability, they are widely used in thermal evaporation coating technology (such as resistance heating evaporation).

The tungsten boats, baskets and filaments are manufactured from high grade tungsten. Of all metals in pure form, tungsten has the highest melting point (3422°C / 6192°F), the lowest vapor pressure at temperatures above 1650°C (3000°F) and has the highest tensile strength. Tungsten also has the lowest coefficient of thermal expansion of any pure metal. This combination of properties makes tungsten the ideal material for evaporation sources. During evaporation, it can alloy with some materials such as Al or Au. In this case, another evaporation source material should be used such as alumina coated boats or baskets. Other materials useful for evaporation sources are molybdenum and tantalum. 

Tungsten filament is an economical and reliable evaporation source in vacuum coating, especially suitable for small and medium-scale metal coating. When using it, it is necessary to optimize the parameters according to the characteristics of the evaporation material, and pay attention to maintenance to improve the coating quality and tungsten filament life. For high-demand scenarios, it can be combined with technologies such as electron beam evaporation or ion plating to improve performance.

1. High melting point (3422°C): suitable for high-melting-point materials (such as aluminum, gold, silver and other metals) at high temperatures.

2. Low vapor pressure: not easy to volatilize at high temperatures, reducing the pollution of the film layer.

3. Strong creep resistance: not easy to deform after long-term high-temperature operation.

4. Chemical inertness: does not react with most evaporation materials.

1.Resistance heating evaporation: Wrap the tungsten wire into a spiral shape, place the material to be plated (such as aluminum wire), and heat it with electricity to melt and evaporate the material, and deposit it on the substrate.

2.Support material: used to fix the evaporated material (such as granular or sheet material).

3.Special coating: used in conjunction with electron beam evaporation or induction heating as an auxiliary component.

FAQ 

1. Why choose tungsten wire as the evaporation source?
Tungsten wire has a high melting point (3422°C), low vapor pressure and good high temperature stability. It is suitable for evaporating metals such as aluminum, gold, and silver. It is not easy to contaminate the film layer and has a low cost.

2. Does the tungsten wire need to be pretreated before coating?
Yes! The surface of the tungsten wire may adsorb gas or pollutants. Before use, it should be pre-degassed at high temperature (heated to red for several minutes) to reduce outgassing pollution during coating.

3. How to choose the appropriate tungsten wire diameter?
Thin wire (0.3~0.5mm): suitable for low power and small amount evaporation.

Thick wire (0.5~1.0mm): carries higher current and is suitable for high power or continuous coating.

Spiral wire: increases the contact area of ​​the evaporation material and improves the evaporation efficiency.

4. Can tungsten wire be reused?
Yes, but the tungsten wire will become brittle after high temperature use and may break after repeated use. It is recommended to check whether it is oxidized, deformed or thinned, and replace it if necessary.

5. Why does the tungsten wire burn out easily?
Possible reasons:

The current is too large (instantaneous overload or improper adjustment).

The evaporation material is short-circuited (such as aluminum wire contacting the tungsten wire causing local overheating).

Aging of the tungsten wire (embrittlement after long-term high-temperature use).

6. What should I do if the film layer is uneven during tungsten wire evaporation coating?
Check the uniformity of tungsten wire heating (whether the spiral wire winding is symmetrical).

Adjust the distribution of evaporation materials (avoid accumulation on one side).

Optimize substrate rotation/movement (improve deposition uniformity).

7. Will tungsten wire contaminate the coating?
High-purity tungsten wire (≥99.95%) has very little contamination.

If the evaporation material reacts with tungsten (such as titanium), an alloy may be generated to contaminate the film layer, and tantalum (Ta) or electron beam evaporation must be used instead.

8. What is the difference between tungsten wire and molybdenum (Mo) wire?

Selection suggestion: Use tungsten wire to evaporate extremely high melting point materials (such as aluminum), and molybdenum wire can be used to reduce costs for general metals.

9. What materials are suitable for tungsten wire coating?
Suitable for evaporating medium and low melting point metals such as aluminum (Al), gold (Au), silver (Ag), and copper (Cu). It is not recommended to evaporate oxides or highly reactive materials (such as titanium).

10. How to extend the life of tungsten wire?
Slowly increase and decrease the temperature to avoid thermal shock.

Avoid overload and operate according to the recommended current.

Check regularly and replace aging and thinning tungsten wire.

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