Parylene Coating Blog by Diamond-MT

Nano Coating and Conformal Coating:  A Functional Comparison

Posted by Sean Horn on Fri, Feb 03, 2017 @ 07:37 AM

The engineering of functional systems at the molecular scale, nanotechnology encompasses management of individual atoms, combined into effective working units, often complex as machines.   Yielding advantages like enhanced chemical reactivity and strength than larger-scale structures, they offer greater control of the light spectrum and weigh significantly less.  Incredibly small, one nanometer is a billionth of a meter (10-9 of a meter) -- one inch equals 25,400,000 nanometers; more illustratively, a sheet of newspaper is 100,000 nanometers thick.  

The Development of Nano Coatings

Already an interdisciplinary field, nanotechnology continues to cultivate an extensive range of applications.  In addition to building machines at the subatomic level, nanotechnology has been adapted for use as a protective conformal coating.  Nanowires and nanotubes are being developed for use in transistors for printed circuit boards (PCBs) and associated electronic assemblies.  The wires can have a diameter as small as 1 nanometer; tubes can be six times stronger than steel, with half the weight.  Liquid crystal displays (LCDs), bio-nanobatteries, capacitators and microprocessors (Intel) are several other items benefitting from nanotechnology.  Simply because of their size, nano coatings are the most appropriate protective covering for these devices.   Apple-Watch-Waterproof.jpg

Nano conformal films have already proven useful as scratch-resistant coatings, created by combining aluminum silicate nanoparticles to scratch-resistant polymer coatings.  The resultant product better resists surface chipping and scratching for an extensive list of current products, ranging from automobiles to eyeglass lenses.  In another case, a fabric coating has been developed (Nanorepel/First Choice Armor) for bullet-proof vests:  a thin layer of organic nanomolecules on the surface of each fiber freezes up upon impact, locking the sturdy strands in place, markedly limiting the projectile’s destructive effect.

Like traditional conformal coatings, nano coatings protect PCBs through their ultra hydrophobic properties, which repel liquid water and block moisture, preventing its capacity for transporting corrosive ions onto boards’ surfaces.  Some of nano’s specialized uses go beyond the normal applications attributed to conformal coatings for aerospace, automotive, consumer, defense and medical purposes, particularly those aligned with MEMS/nano products. 

          Examples of nano coatings’ utility include: 

  • Nanocarbon conformal coatings have shown efficacy for improving the depth and range of photoelectrochemical response and the long-term stability of zinc oxide (ZnO) quantum dots (QDs), nano-sized semiconductor particles with highly tunable properties. Photocurrent density may be enhanced by a factor of 600%, while producing better electrochemical stability that limits photocorrosion.   
  • Aluminum substrate coated with Ni-P-SiO2-Al2O3 nano-composites was tested to assess the coating’s corrosion behavior, implemented in 3.5%wt NaCl solution. Analytical techniques included electrochemical impedance spectroscopy (EIS), field emission scanning electron microscopy (FESEM) and polarization tests.  Energy dispersive analysis of X-ray (EDX) tests determined SiO2 quantities in the coating; X-ray diffractometer (XRD) evaluations assessed its crystalline structure.  Evidence indicated increasing total nanoparticle composition in the coating improved porosity and decreased CPEdl.  SiO2 concentration of 10 g/L combined with 14 g/L Al2O3 to produce the most positive Ecorr and maximum microhardness (537 μHV), and the lowest corrosion rate (icorr = 0.88 μA/cm2).  
  • Composite coatings of P/nano-WC were subjected to electric contact strengthening (ECS) reinforcement and used to cover a 40Cr substrate. Subsequent coating properties were examined by FESEM, XRD, energy dispersive spectrometry (EDS), and Vickers hardness testing.  ECS-reinforcement transformed the bonding between the nanocomposite and the substrate from mechanical to metallurgical bonding, reducing the film’s level of pores and cracks, while refining coating grain sizes.  Hardness increased from 637 to 885 HV0.1, enhancing overall coating wear performance, improved adhesion strength and densified coating structures, suggesting the efficacy of nano coatings and ECS-reinforcement to improve film wear and strength.

Nano Coatings vs Traditional Conformal Coatings

A conformal coating is applied to an assembly requiring protection; this coating covers and seals the device’s working components, delivering reliable protection against intrusive elements.  Nano coatings are emerging as viable alternatives to traditional conformal coatings for protecting PCBs.  This is especially true for mobile electronics, including biomedical devices.  In addition to hydrophobicity, nano coatings repel oils (oleophobicity), with low viscosity and solids’ content. 

Nano coatings are functional at far finer film layers than competing coatings. They respond well to biomedical concerns of personal safety and environmental protection because they are far more benign than such solvent based wet conformal coatings as acrylic, epoxy, silicone and urethane; curing is generally unnecessary, or minimal, even when applied with an atomized spray applicator. 

To the extent that nano coatings are applied by spray procedures, they resemble traditional wet conformal coatings -- acrylic, epoxy, silicone, urethane –which use this similar liquid application approach (as well as brushing, dipping, etc.).  However, nano coatings are increasingly applied via single-step plasma deposition techniques, without curing, closer to parylene’s chemical vapor deposition (CVD) methodology.  

Because they are nanotechnology-based, nano coverings are better suited for MEMS/nano applications than most conformal coatings.  They are stronger, lighter-weight, and far more amenable to the confined special requirements of microscopic technologies.  This makes them a better choice for much biomedical technology, particularly for devices implanted within the human body, which must operate continually, and in many case without fail, to assure the patient’s health.  Nano superiority for these many biomedical functions does not diminish their value as coating for agricultural, automotive, consumer goods/appliances, industrial metals, and marine coatings’ purposes, among many other applications.

 

 

 

Tags: parylene, conformal coating, nano coating