Parylene Coating Blog by Diamond-MT

Parylene C vs Parylene N

Posted by Sean Horn on Tue, Feb 17, 2015 @ 11:07 AM

Parylene and It's Uses

Depending on the specific use, parylene conformal coatings can be effective in the range of 0.1 - 76 microns' thickness, far finer than competing coating materials.  Parylene's other beneficial qualities include these multiple capabilities:

  • entirely covering any substrate to shield it from potential environmental damage,
  • pinhole-free coverage/protection at thickness levels finer than other materials,
  • a completely homogeneous surface, providing a reliable barrier against caustic solutions, acids and water vapor,
  • electrical insulation with low dielectric constancy and high tension strain,
  • thermal stability between -200 °C to +125°C, and
  • adaptability to highly complex coating problems, including surfaces with crevices, points, sharp edges, or exposed internal surfaces.   

In addition to consumer and industrial products, conformal coatings have a wide range of military, aerospace, medical biocompatible and implantable material uses.  The two most common, commercially available members of the parylene family are Parylene N and Parylene C.  Although Type N is the most fundamental of the parylenes, Type C is more widely applied as a product/component coating. 

Comparing Parylene N with Parylene C

Parylene N is an entirely linear poly(para-xylylene) material with exceptional crystalline properties, the most basic of the parylene series.  It has a higher dielectric strength than Parylene C; its dielectric constant value measured in volts/mil at 1 mil, is 7000 and is independent of frequency, remaining relatively constant through frequency changes.  N's higher level molecular activity during deposition generates greater crevice penetration than Type C, making it superior for coating complex topographies.  

The second commercially available member of the Parylene series, Type C parylene is also the most widely used.  It is produced from the same raw material (dimer) as Parylene N.  However, unlike Type N, it is classified as a poly-monochoro(para-xylylene).  As a conformal coating, Type C offers a valuable alliance of electrical and physical properties that distinguish it from Parylene N.  These result from a different chemistry, characterized by a chlorine atom on Type C's benzene ring, replacing one of Type N's aromatic hydrogen atoms.  The result is low chemical, moisture, and vapor permeability, making it particularly useful where protection is needed from corrosive gases.  In comparison to Type N, Parylene C demonstrates a lesser throw-capability, generating a lower reduction in crevice penetration-activity.  At the same time, Type C has a faster rate of deposits on substrates, in comparison to Type N.  

Further Distinguishing Properties and Characteristics                

Additional differences between Types N and C parylene are displayed in Table 1.  

Table 1:  Electrical, Mechanical and Thermal Differences 

Properties Under Analysis

Parylene N

Parylene C

Electrical

 

 

Dielectrical strength/limited duration (Volts/mil @ 1 mil)

7,000

6,800

Dielectrical constant: 60 Hz

2.65

3.15

1,000 Hz

2.65

3.10

1,000,000 Hz

2.65

2.95

Dissipation factor:  60 Hz

0.0002

0.020

1,000 Hz

0.0002

0.019

1,000,000 Hz

0.0006

0.013

Mechanical/Physical Properties

 

 

Tensile strength, psi

6,500

10,000

Tensile strength, MPa

45

69

Yield strength, psi 

6,300

8,000

Tensile Modulus, MPa

2,400

3,200

Water absorption

0.01%/24 hour

0.06%/24 hour 

Gas permeability  

 

 

Nitrogen

7.7

0.95

Oxygen

30

7.1

Carbon dioxide

214

7.7

Sulfur dioxide

1,890

11

Chlorine

74

0.35

Transmission, Moisture Vapor

1.50

0.14

Thermal Properties

7.7

0.95

Melting temperature

410'C

290'C  

Thermal conductivity

3 cal/sec

2 cal/sec

Both Parylene N and C are exceptionally impervious to the effects of corrosive chemicals and exhibit low levels of trace metal contamination.  The faster deposition rates for Types C and N make them highly applicable for a more extensive range of uses than other parylene types.  As the evidence suggests, both N and C have their own recommended applications.  

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Tags: parylene, parylene C, parylene n