|This can be critical so important to know due to the length of the machine required and the imaging technology used in the conformal coating AOI.
The first question to ask is are the PCBs 3D in nature or are very flat? This helps determine whether we use camera or parallax free scanning technology?
Parallax is defined as a displacement or difference in the apparent position of an object viewed along two different lines of sight, and is measured by the angle or semi-angle of inclination between those two lines.
How this relates to conformal coating AOI is that with a fixed camera or a standard scanner the camera is at a fixed point and the circuit board with its 3D components may have “shadows” where the camera cannot see down the side of the components. This can be seen in the two photos below.
Take a look at our Conformal coating AOI Parallax link here to understand the issues more.
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First, in standards a critical distinction needs to be made between the user of a conformal coating and the manufacturer of coating. The Interconnections & Packaging Conference (IPC) standards are very good for both these areas and their details can be found on http://www.ipc.org.
For manufacturing you need IPC-CC-830B which details all the hoops a manufacturer has to jump through to self-certify the quality of their product.
For production purposes you would need either the IPC A -610 standard or the IPC –HDBK-830. The first gives some minor references which are of limited help except for specifying acceptance criteria. However, the handbook is a compilation of the conformal coating industry’s practical knowledge and will help designers & users of conformal coatings to understand the practical implications of selection, application and inspection, explaining in detail how to achieve the best results.
You should also be aware that right now the IPC standards on Conformal Coating Inspection are being reviewed and you can join the debate on the IPC techlink.
Another good resource on topics like conformal coating defects are the Technical Bulletins from SCH Technologies.They covered the full range of conformal coating defects and this will help in the inspection stages.
Click Conformal Coating Inspection FAQs to find out more about this and other issues relating to the process.
The ideal environment for inspection of conformally coated PCAs is within an inspection booth of some description.
The work station should be designed to be comfortable as the operator needs to concentrate on the operation at hand. If you provide the perfect conditions where an operator can easily inspect conformally coated circuit boards without fatigue to body or eyes then this will provide the highest quality results for the conformal coating process.
The booth will provide a darkened area with a UV light fitted inside to allow the fluorescing coating to be examined. Also, the UV light used should be screened from the operators eyes since this could have health issues.
Finally, the environment needs to be safe to use. It should be possible that extraction can be fitted if required to take away any solvent fumes produced due to solvent based coating being used within the confines of the booth.
SCH Technologies have designed, manufactured and use a range of purpose-built, compact UV inspection & finishing booths for conformal coating inspection that have been optimised to offer the best inspection environment without compromise to health & safety, coupled with ergonomic design to minimise operator fatigue.
Anyone who uses a selective robot system for applying conformal coating knows that the system can go wrong. The robot dispenses a liquid. This automatically introduces variables that can go wrong in a variety of ways including
- The coating drying out in the valve leading to a blockage or misdirected coating onto the board
- The material running out and not enough deposited
- The PCB put in the wrong way or the wrong PCB for the program put in the machine
- A component out of alignment leading to a collision of the valve with the board
- The wrong viscosity put in the machine or the viscosity changing with temperature
- The material curing in the machine causing a blockage
It is possible to engineer many of these problems out with options purchased at the time for the selective robot. But, ultimately, no manufacturer of material or equipment will guarantee no problems with their process. So, a conformal coating inspector is needed to check the quality of the process.
Yet, why is this the last part of the coating line that is generally not automated. The rest of the line is and the majority of an assembly line is. But, in conformal coating the general industry still relies on an operator visually inspecting a circuit board by eye under UV light. However, it is well known that operator fatigue leads to errors in inspection. Therefore, PCBs that are coated incorrectly will get past the inspectors.
Hence, an Automated Conformal Coating Inspection System can be used to remove the operator error in the line and improve the process.
What is the best wavelength range for optimal stimulation of the fluorescent effect in the conformal coating?
The optical brightener within the conformal coating will glow at a wavelength range between 300-400nm. That is what most of the manufacturer of UV lights are specifying in their tubes and is classed as UVA light. However its maximum peaks are at 365nm and 450nm.
The single & double inspection booths can be used in ambient light and have UV tube lights built in. the system was designed for inspecting PCB’s with a UV trace present in the coating and as such is black inside. However, additional light shielding may be advisable if the ambient light is very bright as it works better in the dark.
Click Conformal Coating Inspection Equipment FAQs to find out more about this and other issues relating to the process.
Conformal coating inspection is the final and one of the most important stages of the conformal coating application process. But it is still to this day a process that 99% of companies complete manually.
So, why is this the case? In general automated conformal coating inspection is a difficult process. Inspecting a UV fluorescent, transparent coating on top of a complex 3D PCB is not the simplest process for an Automated Optical Inspection (AOI) system.
Until now. Modus now offer automated conformal coating inspection systems which work and operate to the IPC criteria in an effective manner. It is has took a lot of development for them working in conjunction with coating companies but the result is a range of systems which successfully inspect PCBs, is practical to use and is realistic in pricing. Now, SCH is working in conjunction with Modus to offer these systems globally.
So, if you want to remove the final manual process from the conformal coating line you should contact us directly click Modus Automated Conformal Coating Inspection to read further information on these systems.