How Nano Coatings Affect Stencil Performance in SMT Printing

The undersides and edges of solder paste stencils are treated with a thin layer of nano coating, which is oleophobic (oil repellent) and hydrophobic (water resistant). This makes the surface non-stick, which lowers the number of cleaning cycles needed for the printing process using solder paste. The less than 5 nanometer coating does not alter the stencil's size or shape upon application; instead, it forms a tiny bond with the stencil foil.JLCPCB offers nano-coated stencils that leverage this technology to enhance printing efficiency and reliability.

Because there isn't any paste on the bottom of the stencil to transfer to the PCB during the subsequent print, bridging is decreased and the subsequent print will be just as good as the first one. Because now there is less solder paste to remove, which also decrease the frequency of underside cleaning. I've observed clients go from cleaning after each print to cleaning after every 20 prints in certain instances. This article examines the definition, varieties, and print quality, dependability, and return on investment of nano-coating in comparison to conventional SMT stencils. Visit the page and order your nano-coated stencil now from JLCPCB with no any extra cost.

Problem with Traditional Stencil Processes:

Solder paste must stick to the above layer of stencil while applying, but it should not remain at the lower portion of the stencil. If it sticks to the aperture walls and bottom side may cause problems such as solder paste smearing and solder missing.

In order to overcome this intractable manufacturing limitation, more sophisticated boards must frequently have their bottom sides cleaned after each print! This misstep has the unintended consequence of slowing down the entire SMD production line and failing to address the root cause of the issue of rising cleaning material costs.

Smart Solution with Nano-coated Stencils:

The stencil's bottom and aperture walls are permanently coated with an anti-adhesion effect, while the top side remains untreated. Because this nanocoating is only a few nanometers thick, the old stencil's dimensions remain unchanged.

An industry-proven technique that produces noticeable and instantaneous improvements from the first print is nano coating. The qualities of nanomaterials that can be used with stencils are the subject of numerous ongoing studies. By lowering the stencil material's surface energy, nano-coatings stop solder paste from adhering to undesirable regions. The printed solder paste depositions are therefore more consistent, clean, and repeatable.

The Science Behind Nano Coating

These are sometimes referred to as nanotechnology coating or nanocoating. It is basically liquid polymer that contains nanoparticles. Usually made of silica or titanium dioxide, these nanoparticles produce an incredibly thin and transparent protective covering. At the nanoscale level, which is normally 125 um it forms bond with stencil materail and make it nano stencil.

The precision and longevity of nano coatings are distinguished by their extremely uniform and smooth surface, which makes them perfect for intricate stencil designs. Additionally, they provide resistance to abrasion, wear, and chemical exposure.

Cost Drivers in Stencil Printing:

The main cost areas in solder paste printing include:

• Regular cleaning of the underbelly
• Waste from solder paste
• Defective yield loss
• Time spent on rework and reprinting
• Cleaning supplies and equipment

Over time, these ongoing expenses mount up, particularly in settings with large volume. It is frequently necessary to clean standard uncoated stencils after each print, particularly when dealing with fine-pitch components (SAR < 0.55). Cleaning frequency is decreased to once per 20 prints when using stencils coated with nanoparticles.

• One board is produced every minute using an uncoated stencil.
• Two boards are printed each minute using a nano-coated stencil.

For PCB assembly processes that produce large quantities, this productivity doubling is revolutionary.

Types of Nano-Coatings:

There are mainly two types of nano-coatings:

1. Self-Assembled Monolayer (SAM) Coatings:

• Thin coating (2–4 nanometers)
• Applied by wiping onto the stencil surface
• Usually invisible and transparent
• Users of stencils can easily reapply
• Minimizes bridging and underside cleaning
• Less resilient; gradually fades with abrasion or washing

2. Ceramic Nano-Coatings:

• Thicker coating (2–4 microns)
• Sprayed on and dried with specialized tools
• Includes a UV indicator or coloured dye for visibility
• Strong and resistant to abrasion
• Improves transfer efficiency, particularly for area ratios < 0.66
• Cannot be reapplied by users

In comparison to uncoated stencils, experimental research has demonstrated that ceramic nano-coated stencils can increase solder paste transfer efficiency by as much as 22%, particularly for small component footprints as 01005 and 0.4 mm BGA. Conversely, SAM coatings produced inconsistent outcomes, occasionally reducing transfer efficiency for low surface area ratios.

Choosing Between SAM and Ceramic:

Choose SAM if:

• You're producing prototypes or short runs
• You need a quick and affordable coating
• Your stencil has large apertures

Choose Ceramic if:

• You're doing high-volume production
• Your board includes fine-pitch QFNs, BGAs, or 01005s
• Long-term durability and efficiency matter most

Conclusion:

In conclusion, compared to conventional SMT stencils, nano-coating technology offers a notable performance improvement. Future articles on the same subject will address factors like ROI and soldering testing. Because they increase overall yield and decrease the frequency of cleaning, nanocoating's are beneficial. The return on investment, particularly with ceramic coatings, is rapidly realized within a few hundred boards, despite the initial cost being higher. Nano-coated stencils are a clever, cutting-edge option for electronics designers and SMT process engineers seeking great precision and dependability.

Electronics are introducing smaller components and tighter pitches as SMT designs advance. Larger SMD pads can be used with traditional stencil services, but as technology advances, nano-coated stencils are becoming available.  Water, oil, and solder paste flux are all repelled by nano coatings because they are oleophobic and hydrophobic. Improved transfer efficiency, less need (or frequency) for underside cleaning, and less bridging after printing are some advantages of employing these coatings.

Nano-coatings on SMT stencils come in two varieties. The Self Assembled Monolayer (SAM) coating is the first. The underside or board side of the stencil, where the foil meets the printed circuit board (PCB), is where SAM coatings are manually applied. These coatings are usually undetectable and range in thickness from 2 to 4 nanometres. SAM coatings can be renewed after they finally wear off. These coatings' main advantages are less bridging and less underneath cleaning. Let's take a closer look at both of them. The other one is ceramic based.JLCPCB offers nano-coated stencils, and your first order can be made free of charge.