Context:
Many conformal coatings have a little wettability and a low adhesion due to reasons such as the structure of the conformal coating itself, the coated surface properties, or residues that end up being present on components in consequence of manufacturing methods.
Problem:
This phenomenon qualified as « dewetting » generates quality defaults that are to be repaired in line or offline, affecting the global conformal coating line’s quality and productivity performances.
EXELSIUS’ solution:
In response to this problem, EXELSIUS has developed a process solution based on blown air plasma at atmospheric pressure integrated in a specific patented architecture with its automatic programming feature. Thereby, a selective surface activation is achieved, enhancing the wettability of the surface that is to be coated.
As for the embedded technology, blown air plasma at atmospheric pressure consists of generating an electrical arc in air between two electrodes, and blowing this air charged with polar chemical functions linked to Oxygen and Nitrogen molecular structures; these polar functions are grafted in this way to modify the chemical structure of the first 15 nanometers of the treated surface. As a result, Van der Walls forces are generated that improve the surface’s wettability.
Currently on PCBAs, the measured surface tension can be significantly lower than 38mN/m, which is considered as insufficient (measurements are sometimes below 34mN/m). EXELSIUS’ solution typically enables to raise the surface tension from 34mN/m to 46mN/m, above the 38mN/m standard. This is obtained risk free with regards to components’ alteration, thanks to the proprietary algorithm allowing automatic programming of the plasma torch’s 3D trajectory.
The XPS analysis demonstrate the wettability improvement just like the chemical adhesion.
The broad array of conducted trials enable to conclude that the blown air plasma at atmospheric pressure used in combination with, and only with, EXELSIUS’ process integration:
- Increases significantly the wettability of the activated product and the conformal coating’s adhesion.
- Does not degrade the electrical characteristics and specifications of any active or passive components within the component’s specifications.
- Does not degrade the optical specifications of photosensitive components within the component’s specifications.
- Does not cause abrasion or alteration to the PCBAs’ or components’ surfaces.
- Does not generate any ESD problem.
- Still enables manual PCBA’s repairs.
Context:
Coating material commonly use 365nm UV tracer to enable automated and visual inspection of the conformal coating. Some material and especially FLUORINATED POLYMER are applied in very thin layers and tracers used can be photo illuminated only under 254nm UV-C wavelength source.
Problem:
With a small thickness and a poor level of tracers, the inspection station required a high intensity UV light. However, using a UV-C source on a visual inspection equipment can seriously injured operators’ eyes. Also, the low amount of tracers required a low quantity of the visible light to enable enough contrast and therefor clearly see the coating on the PCBA.
EXELSIUS’ solution:
EXELSIUS solution was to modify its standard visual inspection equipment the XVIEW. The equipment is using 365nm LED as standard to control and inspect common coating material. In order to be able to see the FLUORINATED POLYMER (3M™ Novec™ 2704), some upgrades were required:
- Integrate an UV-C 254nm source
- Reduce to minimum the visible light inside the equipment
- Avoid any UV-C light to escape from the XVIEW
In addition, inlet and outlet shutters were added to prevent any UV-C contact with the operator.
The tests performed with wet and dry conformal coating are positive and allowed any operator to inspect the board and clearly identify coating material on the board.
As a solution provider EXELSIUS has adapted and customized its standard equipment to meet specific customer requirement in order to fully satisfy their needs.
UV CURING : WHAT IS IT ?
Curing or polymerization involves changing the state of matter, meaning a product applied in liquid or paste form becomes solid after irradiation.
UV cross-linking is a specialized field. It requires to determine the power, the time, and more specificaly the UV exposure for the curing process to operate properly.
There are two types of cross-linking:
- Radicals are released by UV radiation and trigger polymerization. Cross-linking can be controlled and executed in several steps.
- Cationic cross-linking releases acids that initiate polymerization. Once the reaction is triggered, it cannot be stopped.
UV curing is the polymerization of a material when exposed to ultraviolet light.
UV ranges from 100nm to 400nm. There are various compositions of UV deposition and protection products, requiring different UV wavelengths to cure.
Either over a spectrum covering a complete range from UV-A to UV-C rays, referred to as a « UV Arc lamp »; or over a specific UV-A wavelength, known as a LED source (typically 365nm or 395nm).
A majority of UV conformal coatings are deeply cured through UV-A and on the surface through UV-C.
The combination of time and intensity defines the exposure dose, which is independent of focusing. Here, the gray and orange curves have undergone the same dose but with a different focus.
Materials have an intensity threshold to initiate curing, which must be maintained for a given time to complete the process (free radicals). Any dose below this threshold does not allow for complete curing and may have a negative effect, hence the importance of controlling all these parameters.
WHY UV CURING?
Productivity is a key focus in today’s and tomorrow’s industry development.
UV technology addresses this need by offering minimal floor space requirements, reduced electrical consumption and short production cycles compared to other existing processes.
Equally important is the environmental impact. It is reduced thanks to the absence of solvents in the used coatings. As a result, not only do curing lines require no solvent reprocessing, but the energy impact is also greatly reduced.
With the will to excel in the above key points: EXELSIUS offers a range of UV curing ovens and supports you in improving your production processes.
EXELSIUS UV TECHNOLOGIES
EXELSIUS has developed a range of UV ovens with a unique design that ensures real-time process control.
The principles are focused on managing key curing parameters, namely intensity, dose, time, and temperature. Closed-loop regulation allows to set the dose and maintain the necessary intensity over time.
Our equipment enables the control and adjustment of the process eliminating any drift throughout production.
Regardless of the used module, EXELSIUS’ patented regulation ensures process reliability and compensates the potential UV source aging by measuring and correcting UV power in continuous production.
The required UV exposure profile is thus maintained and monitored over time. This proprietary function enables to measure, adjust and ensure the appropriate insulation (intensity and dose). In addition, this feature is central for sending process data to the MES and granting production traceability. Else said, a key factor for qualitative production monitoring.
EXELSIUS OFFERS TWO UV TECHNOLOGIES:
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Broad Spectrum, UV-C, UV-B, and UV-A
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Spectrum centered around a defined wavelength in the UV-A range (here, 395nm).
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WANT TO KNOW MORE?
We’ll be delighted to provide you with further information and support for your future project!
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