1. Applicability of Parylene in Flexible Electronic Packaging

Advantages

- Flexibility and Thinness:

Parylene (especially Parylene F) has excellent flexibility and can withstand repeated bending (such as thousands of folding of folding screens), and the coating is extremely thin (micrometer level), which is suitable for flexible devices that are sensitive to thickness.

- Chemical inertness and protection:

It has excellent barrier properties against water vapor, acid, alkali, and salt spray (water vapor transmission rate WVTR is as low as 0.1 g/m²/day), which can effectively protect flexible circuits from environmental corrosion.

- Stress-free film formation:

The vapor deposition process can form a uniform, pinhole-free film on a complex structure to avoid mechanical stress damage to sensitive components.

Limitations

- Low mechanical strength:

When used alone, it has poor wear resistance and may need to be reinforced with polyimide (PI) or elastomer.

- Thermal stability limitation:

Standard types (such as Parylene C) usually have a long-term operating temperature of ≤80°C. For high-temperature scenarios, Parylene AF4 (resistant to 350°C) should be selected.

2. Impact on dielectric loss of high-frequency 5G signals

Key parameters

- Dielectric constant (Dk) and loss tangent (Df):

- Parylene C: Dk≈3.1, Df≈0.020 @10 GHz

- Parylene F: Dk≈2.4, Df≈0.0008 @10 GHz

- Parylene AF4: Dk≈2.3, Df≈0.001 @10 GHz

5G frequency band adaptability

- Sub-6GHz (3-6 GHz):

All Parylene types have low losses (Df<0.02), and the impact can be ignored.

- Millimeter wave (24-100 GHz):

- Parylene F/AF4 performs better (Df<0.001), and the signal attenuation is significantly lower than Parylene C.

- For example, at 28 GHz, the loss of Parylene AF4 is one order of magnitude lower than that of Parylene C, which is suitable for high-frequency antenna packaging.

Design suggestions

- Low-loss models are preferred for high-frequency circuits:

Parylene F or AF4 is preferred, especially for millimeter wave applications.

- Coating thickness control:

The skin effect of high-frequency signals is significant, and too thick a coating will increase the loss. The recommended thickness is ≤10μm.

3. Comprehensive application suggestions

- Wearable devices:

Applicable to Parylene C/F (balance between cost and performance), but it should be noted that long-term contact with sweat may reduce adhesion.

- Folding screen packaging:

Parylene AF4 (bending resistance + low dielectric loss + low friction coefficient) is recommended, and it needs to be matched with a flexible substrate (such as PET/CPI).

- 5G antenna module:

Parylene F/AF4 must be used in the millimeter wave band, and the coating uniformity must be optimized to avoid signal phase distortion.