Conformal Coating Innovation: Tilt Function Brings More Coverage to Vertical Parts

Printed circuit boards (PCBs) are becoming ever more complex and assemblies are being packed with an ever-greater component density and surface mount technology (SMT) components that get exposed to harsh and rugged environments. Common coating methods aren’t equipped with the precision or speed to handle applying conformal coating to these kind of assemblies; coating machine equipment manufacturers are constantly establishing much better process control tools, software application, equipment and coating compounds in response to this need. Client needs and emerging innovation have led to the adaptation of archaic conformal coating equipment to automated fluid dispensing systems that can better address this need. Adaptations of dispensing valve applicators, fitting of a high-speed fluid dispenser to coating machines and developments in conformal coating compounds are just a few of the technology that has actually enabled the manufacture of advanced electronics.

Tilt Action

Fluid dispensing equipment that has the capability of flow coating and outlining the No-Zone or sensitive areas are helped by pneumatic tilt action throughout the process of coating machines. In the past, conformal coating machine could not coat the bottom or sides of components on PCBs, but that restriction was lifted off with the advent of four-axis tilting capabilities. They are now equipped with a tilt accessory on the arms to coat all four sides of the component and areas that formerly could not be reached with the traditional vertical approach.

The vertical angle of the dispenser can now be tilted to about 35° maximum in majority of the machines and hit the right, left, back, or front of difficult-to-reach locations and components. Four Position Tilt capabilities enable the machine to coat all the sides of a component with accuracy.

Four-Axis (X,Y,Z U) + Tilt Action

Some coating machines have a four-axis + tilt application that permits further functionality for the fluid dispenser and has tilt and rotation (±180°) activities for dispensing conformal coating on vertical services and underneath the components. The dispensing action can gain access to tight and hard to reach areas that are impossible to coat with a basic downwards spray pattern.

Coating Specifications and More Functionality

Conformal coating for PCB advancements has allowed for numerous desirable specifications. The spray coating patterns of automated fluid dispensing systems usually vary from about 0.125” (3.175 millimeters) to about 2” (50.8 millimeters) and the variation is attributable to the height of the dispenser from the substrate. You can easily achieve thicknesses of 0.002" (0.051 millimeters) and beyond with a single pass of the dispenser. The thickness of the coating is managed by the machine speed and the flow regulator situated on the spray valves.

This repeatability and accuracy aspect provides the advantage of eliminating much if not all of the manual masking of the PCB. However, success or failure doesn’t simply depend on the application method but on the capabilities of the machine. There are now conformal coating machines that have the capability to access almost all required coating areas on the PCB while avoiding keep-out areas. Often, when spray valves alone can’t gain access to an area or coverage is too much in an area, a separate needle is used in the dispensing valve that also has optional tilt capabilities. This setup can then be incorporated into the coating machine’s fluid dispensing system for added functionality.

Conformal coating machines have evolved to be able to coat vertical parts and hard to reach areas by using innovative tilt functions and optional needle systems as required for conformal coating PCB assemblies. When procuring a fluid dispenser system for your facility, it is essential that all facets of the required access of motion are thought through, evaluated, and matched toward what you are trying to achieve for your business requirements. It is also essential to explore the necessary axes of motion required to meet your objectives in order to have a successful result.

This article is brought to you by Anda Automation – the conformal coating and fluid dispenser specialist.

Acrylic Coating Thickness - How to Achieve The “Sweet Spot”

You have the hardware and software. You have got the conformal coating machine. You have got the software that controls the spray of the board. With the right mix and amount of spray, the high speed fluid dispenser applies a pattern of coating to your PCBs. Now your conformal coating PCB is ready for review. The inspection shows that while the quality of coating was good, the thickness was unevenly applied.

This is a situation you want to avoid. As a technician or engineer, you have to ensure that the coating machine program apply the conformal coating thickness evenly on the circuit card assemblies. This article will show you how to ensure the coating program give you the right thickness when applying acrylic coating to your machine, and how to test if the product is compliant to the specification.

Standards for Conformal Coat Thickness

The most popular conformal coatings used in industry today are Humiseal 1B31 and MG Chemicals 419C The material is relatively cheap, easy to use and provide excellent moisture protection. There are industry standards for conformal coat thickness for acrylics and when adhering to IPC-610, type AR conformal coatings, and the thickness should be in between . 002” and . 005. ” MIL-I-46058C indicates that the thickness should be . 002” +/- . 001. ” Most manufacturers aim between about . 002” to . 003,” and meeting that guideline will ensure that you stay within the two major thresholds of the two major specifications called out in the standard.

The standard is in the company's product specification sheet. Everyone who is involved in the process should know what the standard is. When calibrating the conformal coating machine, the right thickness must be applied to the finished substrate. If the standard thickness is not achieved, then the coating fails to protect the final PCB from moisture ingress.

With the correct coating machine that match the PCB requirement, the standard can be met. Now it is up to the programmer to set the right pattern and amount of passes in the software to ensure the correct thickness is achieved. Too many or too few passes results in improper conformal coating.

All it takes is for the programmer to adjust the software setting to achieve the desired range. There are ways to measure the thickness of the conformal coating - either using a manual process or testing equipment.

Coating Thickness Measuring Techniques

It is important to achieve the standard of the desired thickness, regardless of the conformal coating equipment used. This can be achieved by measuring the coating and calibrating the process. There are two categories of measuring tools - dry and wet film measurements.

Dry Coating Thickness Measurement

Conformal coating for PCB dry film measurements are made after the coating dries enough for any contact made with the coating, so that any contact made during the process won’t damage the coating. For this method, measurements are taken on unencumbered, flat and cured surface of a PCB, or on a coupon processed with the part.

Test coupons are normally used to measure the coating as it is easy and affordable.. The coupons also provide a record for the quality assurance department to look over to make sure the coating characteristics and parameters are up to par with the specifications and can be sprayed the same time that the PCBs are.

One way to spray coating to test involves procuring some coupons made up of nonporous material, such as glass or metal. Glass slides that are like the ones you used in biology or chemistry work really well for this. Test coupons made out of the same material that the PCB you are spraying usually work the best. The “sticky dot” method works really well, too. Identify the areas you want to take a measurement and measure it with micrometers or an indicator that’s accurate to 12. 5+_2. 5µm on, and begin the test by spraying it with the acrylic material.

Dry the area. Then measure the area once more. The difference between the beginning and end measurements will be your record for thickness. Write these measurements down in a standardized record that shows proof that thickness was calibrated before beginning a run of production. Run other tests periodically to ensure the process remains correct.

Another dry method that is used frequently is testing equipment that utilizes eddy currents to test conformal coat thickness. It is a little more expensive, but involves a non-contact technique. The measurements involve lightly placing a test probe head on the surface of the coating to get an almost instantaneous readout. If the production amount of PCBs on conformal coating printed circuit boards is high, you might want to invest in this method. The measurement devices are extremely accurate, up to thin films of 25-50 um and ±1 um for a device such as the Positestor 6000. This is recommended for high volume because they are very quick to display measurement readings.

Wet Film Conformal Coating Measurement

This method involves using a wet film gauge to measure the coating while it’s still wet. This allows operators to test and help accomplish quality assurance before the coating dries.

There are advantages to using this method. For one thing, applying to much conformal coating costs your business a lot of money, and it’s also useful for conformal coating processes where dry coating thickness can only be measured by using destructive methods.

How to do it: the wet film gauge is placed into the wet conformal coating after application until the teeth of it contacts the substrate or surface of the components measured. There are measurements on the gauge that indicate how thick the coating is. Count the measurement line that the conformal coating has risen to. You will be able to tell the dry film coating thickness by calculating it from measurement s derived from the solid resin content of the coating on the PCB.

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