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Selectivity in Conformal Coating

Utilize selectivity and start coloring inside the lines

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As consumers, we expect our electronic devices and vehicle electronic systems to work reliably, regardless of environmental conditions or rugged handling. In today’s vehicle market, more electronics are used than ever before, driving the potential for a higher volume of failures. Moisture, for example is one of the biggest “enemies” of electronics, which is why manufacturers use conformal coating processes to protect and improve board yield and reliability. Coating polymer materials onto a PCB assembly can dramatically improve electronics reliability and protect them against moisture. The coating area must be selectively chosen to avoid proper functional areas, such as connector leads. Use of selective, automatic coating equipment can help improve cost reduction by mitigating strayed and drifted coating material. An automated conformal coating process ultimately leads to yield improvement by ensuring coating material is placed only where needed within tight tolerances.

In the electronics assembly industry, keep-out zones (KOZ) commonly define the areas where coating material should not be applied to achieve proper functionality. For KOZ, some manufacturers rely on extensive labor-intensive masking and operator rework, an expensive undertaking in terms of personnel, throughput loss, and material cost. Processes that don’t incorporate automatic equipment can add extra costs to the manufacturing process. 

The use of properly characterized, automated selective coating equipment is a reliable way to increase yield, increase throughput and reduce rework and process costs.

Selectivity Factors and Solutions

Edge definition – Maintaining clear edge definition ensures coating materials are applied only where needed – with less overspray and avoiding keep-out zones. Nordson ASYMTEK’s SC-350 Select Spray Applicator is designed with improved atomization to deliver exceptional edge definition, thinner and more uniform coating thicknesses at increased speeds, and to significantly reduce the effects of overspray and cobwebbing (Figure 1). The left image in Figure 1 illustrates the Pass Width, the dimension of complete coverage with a single coating pass. The middle image defines Edge Definition as the spread of material beyond the pass width with a single coating pass. The image on the right illustrates overspray or material splash extending beyond the main coating pass and edge definition.

Edge Definition Diagram 

Customized, flexible solutions- Choosing the right applicator is not a “one size fits all” decision. Applicator tools are designed to either provide broad coverage or perform finesse detail work. Often, pairing applicators is required to provide both broad coverage and precise coating on the same product.  Nordson Asymtek specializes in customized configurations that offer a comprehensive solution for every application.

While the SC-350 applicator atomizes materials that are high in viscosity and solvent-less, Nordson ASYMTEK’s Select Coat® SC-280 non-atomized film coater is an ideal choice for low viscosity, solvent-based materials. The SC-280 applicator provides high speed, superior edge definition for selectively applying conformal coating materials with viscosities less than 100 centipoise. Even at this high speed, edge definition remains sharp for greater control in avoiding Keep Out Zones.

Nordson ASYMTEK’s SC-400 PreciseCoat® Jet is the optimal choice for reaching locations not accessible by other applicators by using a needle to jet discrete dots. The SC-400 jet is compatible with low viscosity materials that are typically less than 400 centipoise. When using solvent-based materials, film thicknesses of 15 micrometers can be achieved, depending on the material.

Visual programming capability – A software tool specifically designed for conformal coating, together with an integrated camera system, reduces programming time and ensures coating material is applied only where needed. Inferior systems that rely on manual alignment of the applicator tip, or those with distorted optics, are prone to programming misalignment around connectors and devices on the edge of the PCB. This misalignment can lower yield when coating materials end up in keep-out zones. 

Nordson ASYMTEK’s EasyCoat® 6 software generates an accurate image of the product and enables drag-and-drop programming to ensure coating is applied exactly where it’s needed.

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