UV LED Conformal Coating: Top Considerations for Upgrading from Mercury Arc to UV LED Curing

Many electronics manufacturers, PCB assemblers, and electronics manufacturing service (EMS) providers are using UV curing for conformal coating printed circuit boards (PCBs). As a result these manufacturers reduced their VOC emissions, increased production rates, and improved first time quality rates. Now with advancements in UV LED curing technology, these manufacturers have the opportunity to further improve their conformal coating processes to be more competitive.

Read on to learn more about the benefits of UV LED curing technology and the top factors to consider when replacing traditional mercury arc lamp UV curing with UV LED curing for conformal coating PCB applications.

Benefits of UV LED compared to mercury arc UV curing of conformal coatings

The top benefits of UV LED curing compared to traditional mercury arc lamp UV curing include:

  • More consistent and reliable curing process
  • Higher production rates
  • Less downtime - reduced maintenance, longer operating life
  • Energy cost savings
  • Environmentally friendly – no VOCs, no mercury or ozone
  • Even less heat – no damage to heat sensitive components
  • Less space required
  • More process flexibility - instant on/off, adjustable width of cure

This chart provides comparisons of medium pressure arc lamp and UV LED UV curing system technology characteristics.

Mercury lamp and UV LED

Med. Pressure Arc UV LED NOTES
Useful Life (hours) 500 - 3,000* 10,000 + All UV lamps degrade over time, so it's important to understand "useful life", which is the expected operating hours where adequate curing can still be achieved for your process. *Arc lamp life is significantly reduced if the lamp is not kept within a narrow operating temperature range and by the number of on/off cycles. Additive arc lamps have a shorter useful life than mercury arc lamps.
Cooling Needs External Fans - complicated and critical Internal Fans - simple Water cooling sometimes used for all types. In general, UV LED systems require about 10 times less cooling than traditional UV systems and dynamic cooling, like that used in Semray UV LED systems, ensures longevity and optimal operation.
Energy Use High Low UV LED curing systems use 30 to 70% less energy than traditional UV curing systems.
Power Class 200 - 800 W/inch 8 - 22 W/cm2 This is a general indication of the class of curing system, but does not indicate UV energy reaching a substrate. For arc systems this is actually the input power. For UV LEDs their rating is typically the peak irradiance at the emission window. Since there is no standard for energy density ratings of UV curing systems, users need to run tests or obtain data from individual manufacturers.
Wavelength Output Broad - short and long; additive lamps Narrow, nearly monochromatic; 365, 385, or 395nm Wavelength output needs to be a best match for the chemistry formulation being cured. This is normally available from your chemistry supplier. The longer wavelengths of UV LEDs are ideal for gasketing, encapsulating and conformal coating applications where through cure is needed, but surface curing for thin hard coats is challenging.
Lamp Length Up to 110 inches,
Spot cure 		Custom array lengths or modular segments to span across flat conveyor, spot cure Modular UV LED curing platforms like Semray enable quick changes to different wavelengths and less costly upgrades as UV LED technology advances.
Dimming 38 - 100%, step or continuous 40 - 100% continuous Controls typically tied into overall manufacturing line controls to improve process flexibility and consistency. Power supply technology is advancing rapidly to include smart, self-monitoring dynamic controls like that found in Semray UV LED systems.
Warm-up Time ~ 5 min. 0 The instant on/off capability of UV LEDs offer a significant advantage over arc lamps resulting in higher line/machine utilization and production rates.
Restrike Time long, must use shutters 0 The instant on/off capability of UV LEDs offer a significant advantage over arc lamps resulting in higher line/machine utilization and production rates.
Mercury Yes No UV LED offers a safer work environment, more sustainable production process.
Ozone Yes No Short wavelength UV energy generates ozone. Since UV LED does not emit short wavelengths, there is no ozone - you get a safer work environment and more sustainable production process.
Weight Heavy Light UV LED units weight much less, but also the mounting and UV light shielding is significantly less weight.
Form Factor Large, Bulky Compact UV LED is so compact that it is easy to retrofit on existing lines and even use in combination with existing arc lamps for applications that need surface curing. With UV LED there are no bulky cooling/exhaust ducts and external fans.

UV LED curing technology has advanced rapidly with energy output increasing 12% annually. In addition, the use of improved cooling and optics have enabled UV LED curing system manufacturers to develop reliable systems that deliver more UV energy onto the substrate where it is needed. Recently, conformal coating formulators have taken advantage of these UV LED technology improvements to develop UV LED curable materials.

Top factors to consider for upgrading a conformal coating process from mercury arc to UV LED curing

All UV curing processes require the best match between the spectral absorption of the chemistry formulation and the wavelength output of the UV curing system. Additional process parameters such as part dimensions, handling, and production rates, and UV LED system features impact the costs and return on investment (ROI). Finally, it’s important to work with process development partners who can help you implement a successful UV LED curing process with minimal risk. Let’s discuss each of these factors in more detail.

UV LED curable conformal coating formulations

Existing UV conformal coatings are 100% solid, single component, non-flammable, and use dual-cure technology. After coating, the PCB is exposed to the UV energy to cure in seconds. However, a secondary cure, sometimes heat, but most commonly moisture, ensures curing of the coating in shadow areas where the UV energy cannot reach.

Commercially available UV-curable formulations include those designed for use with either broad spectrum arc lamps or UV LED curing systems, and some specially designed for use with UV LED curing only. The former offers the flexibility to use either curing technology, but formulations designed specifically for UV LED’s near monochromatic wavelength output will generally be more efficient with faster production rates. UV LED formulations can also cure thicker coatings providing better protection of the PCB. (From: https://globalsmtseasia.com/articles_&_papers/the-evolution-of-conformal-coating/ )

graphic

Sometimes no secondary cure is needed. For example, if the process uses selective coating, high-viscosity coatings, or low-offset, smaller surface-mount components (don’t allow coating to flow beneath), then the UV LED energy can reach all of the material via line-of-sight to provide complete cure. Your UV LED coatings supplier will specify what wavelength, 395nm is most common, but 365nm, 385nm, and 405nm are also possible, and whether a secondary cure is needed.

Typically, whatever application method you currently use for existing UV coating can be used for UV LED coatings such as automated selective spray, manual spray, jetting, or brushing. So this aspect of your process remains the same.

A few conformal coating suppliers have commercially available UV LED curable resins. More UV LED curable conformal coatings will become available in the future since most conformal coating formulators have R&D programs focused on development now.

UV LED Curing Process and Equipment Options

Production rates, board processing widths and variety/flexibility needed, dynamic versus static cure, wavelength, height adjustments, conveyor speed adjustment, dimming capability, UV energy output, controls integration with coating application line, and conveyor versus benchtop flood system are some of the UV LED curing process and equipment options to consider.

Your existing process and desired production rates are the best place to start designing requirements for a new conformal coating UV LED curing process. For example, if your existing process uses a static cure in a batch process, your desired production rates may dictate using a continuous process using a flat-line conveyor. Or, if you already have a continuous process, then it is likely you can retrofit the line with the UV LED curing equipment given its small form factor.

If you need flexibility to run a variety of products, be sure to consider UV LED systems that can easily adapt to your changing process needs . Typically a modular system offers more process flexibility such as width of cure and quick changeovers to different wavelength output. Other process flexibility features to look for include the ability to cure at a variety of working distances and dimming capability.

Additionally, evaluate the total cost of ownership of the UV LED system, not only the first cost. Compared to mercury arc lamp systems, UV LED systems require significantly less maintenance, energy and spare parts, so operating costs and downtime are much less. However, upgrades to take advantage of the latest UV LED chip technology which is advancing rapidly, can be costly. And your processing needs are likely to change to meet new customer demands. A custom UV LED curing system or systems for specific widths may be more costly to upgrade to the latest UV LED chip technology, both in terms of cost and downtime, because you’ll need to purchase an entirely new curing unit. Look for a system where it is possible to replace only the UV LED array while keeping everything else, i.e. the emission window, housing, cooling fans, power/controls, and mounting system.

Click here to watch the video about the "total cost of ownership" of Noblelight's UV LED curing systems

Low Risk/High Success Process Development & Qualification

The most important factor for ensuring success and meeting return on investment goals when switching to UV LED conformal coating is to find the right partners to guide and support your team. Even in the initial feasibility stage it’s a good idea to enlist help from both resin and UV LED curing system providers because you’ll get better, more realistic information for your specific situation. In addition, you can begin assessing and comparing providers and building relationships with those who are the best fit to help you through testing, trials, and production start-up.

Process Development and Qualification

Find partners experienced in conformal coating who can run tests in their labs or provide loaner UV LED curing equipment to run pilot testing or in-plant trials to prove out your process and production rates. Consider what training and other after sales support may be needed such as maintenance services, phone support, and consignment spare parts. If your operations are global, find partners who also have global operations.

Learn more about  Choosing a UV LED Equipment Provider.

Learn more about  Reducing Downtime with UV LED Curing.