Chapter 3 of our comprehensive guide to stencils discusses when to use nanocoating, what options there are and the benefits they bring to your application.

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3.0 Nanocoatings

With a thickness of no more than 1-100 nanometers, nanocoatings are ultra-thin layers or chemical structures
that are applied to surfaces by a variety of methods and applied to a wide range of substrates and chemically
bond with non-porous surfaces. To put this in perspective, consider the thickness of paint used in the automotive
industry of which is typically 125 microns or 125,000 nanometers.

While they can be one molecule thick, multiple molecular layers can be built up to deliver a particular chemical or
physical property to a surface such as water-resistance (hydrophobic) and oil-resistance (oleophobic).

3.1 Nanocoating SMT stencils

The underside of solder paste stencils can be nanocoated at a typical thickness of ~5 nanometers to provide a
non-stick surface which:

• reduces the number of cleaning cycles required during the paste printing process
• improves paste transfer efficiency for fine pitch apertures

Nanocoating SMT stencils delivers immediate and measurably improved results from the first print and can
also be applied on the production line to previously used stencils.

3.2 When to use nanocoatings

There are a number of factors to take into account when considering whether to nanocoat a stencil:

1. What is the smallest aperture and pitch on the stencil and what is its thickness?

In the case of a large board with large appertures, the benefit of nanocoating is insignificant. On the other
hand, stencil performance can be considerably improved in the case of a dense image with fine pitches and
small apertures.

2. How many prints are you using the stencil for?

If you’re simply printing a prototype, nanocoating is not necessary but where volume runs are concerned,
nanocoating significantly reduces the frequency of cleaning cycles.

3. What paste are you using?

In the case of SMT stencils, the denser the paste you are using, the greater the benefit of nanocoating.

3.3 Nanocoating benefits

3.3.1 Better quality printing

Because the flux is repelled from the aperture walls by nanocoating, there is a reduction in bridging, resulting in
better results. Figure 3.1 below shows the print definition improvements that can be achieved with a nanocoated
stencil, highlighting QFN and 0201 devices after ten prints with no wipe using the same board, same stencil design
and same print stroke.

nanocoating stencils

3.3.2 Improved productivity, reduced costs

Flux-resistant nanocoating applied to the underside of the stencil and stencil aperture walls can boost
productivity and reduce costs for volume runs:
• less underwiping is required
• less downtime for paper changes
• there is less damage to stencil mountings, particularly for meshed stencils, from exposure to aggressive
cleaning solvents.
• lower paper and solvent consumption

nanoclear treated stencil

3.4 SMT nanocoatings available from Tecan

A choice of nanocoatings are available for all Tecan stencils both of which create a robust, abrasion resistant
surface that stands up to repeated cleaning.

• MicroShield is a two-part coating that is applied by Tecan prior to stencil dispatch
• NanoClear® coating from Aculon is supplied in a pouch containing both the primer and nanocoating to be
applied on the production line.

3.4.1 MicroShield

This on-contact coating has a unique chemistry. Upon contact, it forms a self-assembling monolayer that is highly
hydrophobic and oleophobic. It is applied to Tecan’s solder paste stencils after they are cut and prior to dispatch.
MicroShield demonstrates both the printing and cleaning benefits of nanocoating.

MicroShield does not “cure” like a traditional polymer coating but instantly transforms the surface on-contact.
Performance typically improves with time.

MicroShield test results

3.4.2 NanoClear®

NanoClear is a SAMP Coating (Self-Assembling Monolayer Phosphonate) supplied in a two-part pouch and
can be applied by SMT operators to a new stencil on the production line or to an existing stencil to improve
performance.

Aculon NanoClear repels flux which improves print quality, increases efficiency, lowers total costs and enhances
printing with small apertures.

NanoClear SMT Stencil Nanocoating

Application of NanoClear® is very simple. With a
NanoClear® dual wipe, a water source, and just five
minutes of time you can have an SMT stencil that has
been properly treated with a robust and high performing
coating.

3.4.2.1 Applying NanoClear

Step one (unprimed stencil)
Take the clean stencil and hold under running water for a few seconds, if the water
does not wet out evenly onto the stencil (see figure 3.6), then the stencil still has
surface contaminants and needs to be primed with Aculon Primer (Part A).

Uneven wetting

Step two (primed stencil):
After using Aculon Part A rinse the stencil under running distilled or deionised water for at least 60 seconds.
Please note a primed stencil will have an unbroken film of water that should remain on the surface without
beading up for 30 seconds. If the stencil looks like this, then completely dry with a cleanroom wipe and proceed
to the application of Part B.

Step three (treated stencil):
Upon opening, immediately apply Aculon Nanoclear Part B by wiping it on the
stencil for one minute. Wipe off excess coating with a cleanroom wipe. You can
test a stencil’s performance by evaluating if water droplets bead tightly on the
surface (as shown in figure 3.7) and shed from the stencil easily when tilted.

Tight beading on stencil surface

3.5 How long does a nanocoating last?

Aculon states that users typically report 25K print cycles, although durability depends on many factors,
including:
• Abrasiveness of wiper paper/fabric
• Wipe frequency
• Solvent or dry wipe
• pH of under wipe and off-line cleaning solvents
• Solder paste chemistry

In order to maximise durability, Aculon suggests:
• Use soft, non-abrasive understencil wiper paper such as Eco Roll SCER360 or Hyperclean PP4200
• Use a solvent wipe rather than a dry wipe – engineered solvents are best for lead-free no-clean pastes
• Use pH neutral cleaners
• Reduce understencil wipe frequency