Electronic equipment coating cannot be judged by appearance alone

An attractive appearance is also important when coating electronic and communications equipment.

A surface free of dirt. An even finish. Consistent color and gloss. An appearance that fits naturally when the components are assembled.

These are, of course, important aspects of quality.

However, in electronic equipment coating, it can be risky to judge a product as acceptable based on appearance alone.

This is because coating films on electronic equipment may need to provide functions beyond appearance.

These include the following:

• Shield electromagnetic waves
• Provide conductivity
• Provide insulation
• Dissipate static electricity
• Protect component surfaces
• Maintain dimensional accuracy with a thin film
• Prevent foreign matter and pinholes
• Give plastic surfaces functional properties

In electronic equipment coating, the coating film must therefore be understood as a functional surface layer, rather than simply a colored film.

Why are thin films important for electronic equipment?

Electronic and communications equipment are becoming smaller, lighter, and more capable.

Components are smaller, structures are more complex, and assembly requires greater precision. An excessively thick coating film can therefore affect dimensions and assembly.

Examples include the following problems:

• Components do not fit together
• Insufficient clearance
• Coating film builds up around screws or terminals
• Poor contact at connectors
• Covers or housings become difficult to close
• Cracking or peeling occurs in thick-film areas

A coating film that is too thin also causes problems.

• Failure to provide the required functions
• Insufficient hiding power
• Insufficient moisture protection
• Unstable conductivity or shielding performance
• Greater susceptibility to pinholes
• Insufficient durability

In electronic equipment coating, a thicker film does not automatically provide greater assurance.

What matters is consistently forming a thin, uniform film at a thickness that delivers the required functions.

What is electromagnetic shielding paint?

Electromagnetic waves can cause problems in electronic and communications equipment.

Waves from outside may affect the equipment’s operation. Waves generated inside the equipment may also affect nearby devices.

Electromagnetic shielding may be needed to reduce these problems.

Electromagnetic shielding blocks electromagnetic waves and reduces their effects.

A metal housing itself may serve to block electromagnetic waves. However, when plastic housings are used for low weight or moldability, the plastic itself may not provide sufficient shielding.

A conductive coating film can therefore be formed on the plastic surface to provide electromagnetic shielding.

This is the basic principle of electromagnetic shielding paint.

For electromagnetic shielding paint, controlling function matters more than appearance

For electromagnetic shielding paint, an attractive-looking surface alone is insufficient.

What matters is whether the coating film provides the required conductivity and shielding performance.

The checks therefore differ somewhat from those for ordinary appearance coatings.

Examples include the following:

• Is the film thickness correct?
• Is conductivity stable?
• Is the coating film uniform?
• Are there any uncoated areas?
• Are there any pinholes?
• Does it adhere to the plastic substrate?
• Is there any poor contact after assembly?
• Does it meet the required performance tests?

For electromagnetic shielding paint, electrical performance must be checked as well as coating appearance.

Visual inspection alone therefore cannot assure quality.

Film thickness and uniformity matter for conductive coating films

Film thickness and uniformity are very important for coating films intended to provide conductivity.

Insufficient film thickness may make conductivity unstable. Areas where the film is locally thin can fail to provide the required function. Uncoated areas or pinholes can reduce shielding performance.

Applying an excessively thick film creates other problems.

• Poor drying
• Sagging
• Cracking
• Poor adhesion
• Increased costs
• Dimensional defects
• Assembly defects

For conductive coating films, the thickness range needed to meet the required performance must be clearly defined and achieved consistently.

Rather than assuming that a slightly thicker film will be safer, it is important to control precisely the film thickness required for the function.

Adhesion and substrate identification matter for plastic housings

Plastic housings are widely used in electronic and communications equipment.

Plastics are lightweight, easy to mold, and offer considerable design freedom. From a coating perspective, however, they present different difficulties from metals.

The following points must be checked when coating plastics:

• What type of plastic is it?
• Is any release agent left on the surface?
• Is there any oil or dirt?
• Is the surface energy sufficient?
• Is a primer required?
• Could the solvent cause cracking?
• Could the drying temperature cause deformation?
• Can the coating film achieve the required hardness?

Identifying the specific plastic material is particularly important.

Even within “plastics,” materials such as ABS, PC, PP, PBT, and PA differ in coatability. Treating them like metals can cause poor adhesion, cracking, deformation, or peeling.

In electronic equipment coating, always identify the plastic substrate and check its surface condition before selecting paint.

Watch for solvent cracking

Solvent cracking is one of the defects that requires attention when coating plastics.

Solvent cracking occurs when solvents in paint or thinner affect the plastic substrate and cause cracking.

It may look as though the coating film has cracked. However, the cause may lie in compatibility between the solvent and plastic substrate, rather than in the coating film alone.

The following checks are needed to prevent solvent cracking:

• Identify the specific plastic material
• Check the solvent composition of the paint being used
• Check whether an excessively aggressive thinner is being used
• Check the drying conditions
• Check whether coating is being applied to areas under stress
• Check for cracking in preliminary tests

Plastic components may be more susceptible to solvents than metals. Whenever paint or thinner is changed, compatibility with the substrate must be checked.

Why pinholes and craters can become serious defects

In electronic equipment coating and thin-film coating, small defects can create major problems.

Pinholes and craters are typical examples.

Pinholes are small hole-like defects in the coating film. Craters are small depressions in the coating film surface.

In ordinary thick-film coating, minor defects may not immediately cause functional failure. In electronic equipment and functional coating films, however, even small defects can affect performance.

Examples of the risks include the following:

• Unstable conductivity
• Reduced electromagnetic shielding performance
• Insufficient moisture protection
• Reduced insulation performance
• Starting points for corrosion
• Appearance-related complaints
• Peeling in subsequent processes

In thin-film coating, additional thickness cannot conceal film defects. Foreign matter control, degreasing, paint filtration, booth cleanliness, and stable application conditions are therefore important.

Foreign matter control is fundamental to electronic equipment coating

Foreign matter control is very important when coating electronic equipment or precision components.

Even small dirt particles or dust can affect product function or appearance.

Paint is not the only source of foreign matter.

Foreign matter can enter from the following locations:

• Paint cans
• Mixing containers
• Filters
• Spray guns
• Air lines
• The booth interior
• Work clothing
• Gloves
• Product storage areas
• Preceding processes
• Transport fixtures
• Packaging materials

For electronic equipment coating, foreign matter control must cover preceding and subsequent processes as well as the coating room.

In thin-film coating in particular, foreign matter can disturb local film thickness or cause pinholes and craters.

Foreign matter control affects functional quality as well as appearance quality.

Inspection methods for functional coating films must be defined at the outset

Visual inspection alone is insufficient for functional coating films.

For example, electromagnetic shielding paint must be checked for the required shielding performance. Conductive paint requires measurements such as surface resistance. Insulating coating films require checks of insulation performance.

Inspection methods must therefore be defined at the same time as the coating specification.

Check the following items.

• Which functions will be guaranteed?
• Which numerical values will be controlled?
• Which measurement methods will be used?
• Which locations will be measured?
• How many units will be produced between measurements?
• What action will be taken when a result fails?
• Are criteria available for both appearance and functionality?

For functional coating films, the work does not end with application. Quality is assured only when the required function has been confirmed.

Thin films make variation in coating conditions more apparent

In thin-film coating, small variations in application conditions readily appear as differences in quality.

Examples include the following conditions:

• Spray distance
• Gun angle
• Paint flow rate
• Air pressure
• Thinning ratio
• Paint viscosity
• Application speed
• Drying conditions
• Booth airflow
• Product temperature
• Humidity

Differences that were partly hidden in thick-film coating may appear directly on the surface in thin-film coating.

With a thin film, even a small shortfall in thickness may result in insufficient function. Conversely, locally thick areas can cause dimensional defects or poor drying.

Reducing differences in operator skills and standardizing conditions are therefore important in thin-film coating.

Points to watch in Vietnamese factories

Certain points require particular attention when coating electronic equipment in Vietnam.

First is humidity. High humidity can cause poor drying, blushing, poor adhesion, or blistering.

Next is dust. In electronic equipment coating and thin-film coating, small foreign particles can cause serious defects.

Insufficient identification of plastic substrates is another concern. Knowing a part only as “plastic” leads to inadequate checks of compatibility with paint and thinner.

For functional coating films, there is also a risk of judging acceptance through visual inspection alone. An attractive-looking finish may still have insufficient conductivity or shielding performance.

The following controls are important in Vietnamese factories:

• Identification of the specific plastic material
• Compatibility checks with paint and thinner
• Foreign matter control
• Prevention of recontamination after surface preparation
• Film thickness control
• Functional inspection
• Operator training
• Booth environment control
• Drying condition control

The 4M perspectives CoatureVietnam checks

When improving electronic equipment coating, CoatureVietnam checks the 4M perspectives.

Material: materials

• Is electromagnetic shielding paint required?
• Is conductive paint required?
• Is an insulating coating film required?
• Is the paint suited to the plastic substrate?
• Is a primer required?
• Could the thinner adversely affect the plastic?
• Can a thin film still provide the required functions?
• Are the functional ingredients in the paint dispersed consistently?

Method: methods

• Are film thickness criteria clear?
• Are spray distance, gun angle, and air pressure standardized?
• Are foreign matter control procedures in place?
• Is waiting time after surface preparation controlled?
• Have functional inspection methods been defined?
• Are acceptance criteria available for pinholes and craters?
• Do repair methods preserve functionality?

Machine: equipment

• Is booth cleanliness sufficient?
• Is the paint filtration equipment appropriate?
• Is the coating equipment suitable for thin-film application?
• Can the equipment keep drying conditions stable?
• Is a film thickness gauge available?
• Is inspection equipment available to measure conductivity or surface resistance?
• Could foreign matter or scratches be introduced during transport?

Man: people

• Do operators understand the purpose of functional coating films?
• Do they understand that a good appearance can still conceal a functional failure?
• Do they understand the precautions for each plastic material?
• Do they understand the importance of foreign matter control?
• Do they understand the purpose of film thickness control?
• Do managers provide separate guidance on appearance criteria and functional criteria?

From the Management perspective, customer requirements, the scope of functional guarantees, inspection criteria, process capability, and change control must be clearly defined.

Questions for customer visits

For electronic equipment coating projects, sales and technical team members can use the following questions:

• Does this coating film have functional requirements beyond appearance?
• Are electromagnetic shielding, conductivity, or insulation required?
• Has the specific plastic material been identified?
• Has cracking ever occurred with the paint or thinner being used?
• Are film thickness criteria available?
• Where is film thickness measured?
• Are functional inspections carried out?
• Are control criteria available for surface resistance or similar properties?
• Have pinhole or crater defects occurred in the past?
• In which process does foreign matter occur most often?
• Does assembly after coating reveal poor contact or dimensional defects?
• Is functionality maintained after repair coating?

These questions help identify risks that appearance alone cannot reveal.

Conclusion: electronic equipment coating must deliver functionality in a thin, uniform film

In electronic equipment coating, the coating film cannot be viewed simply as an appearance finish.

As products become smaller, lighter, and more capable, coating films must be thinner and provide functionality.

Electromagnetic shielding. Conductivity. Insulation. Moisture protection. Dimensional accuracy. Foreign matter control. Pinhole prevention. Adhesion to plastic substrates.

To meet these requirements consistently, consideration must extend beyond paint to the substrate, surface preparation, film thickness, application conditions, equipment, and inspection methods.

An attractive-looking product cannot be considered acceptable if it lacks the required functionality.

CoatureVietnam views electronic equipment coating as a process that combines appearance quality with functional quality.

Coating the Future with Science and Care.

Putting this into practice, we will support process improvements for thin-film and functional coatings suited to the applications of electronic and communications equipment.