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.
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 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.
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.
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.
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.