The reliability of electronic components and circuit boards depends greatly on the quality of the insulation film, which protects internal circuits from external environments. Among the available coating methods, dip coating is widely used in insulation film formation because it enables uniform thin film coverage on both sides of substrates, even those with complex geometries.
However, despite the simplicity of the basic principle, consistently achieving a high-precision film requires strict control of conditions at every process stage. This article outlines the essential process parameters, as well as solution and environmental conditions, that are critical for successful insulation film formation using dip coating.
Withdrawal Process Conditions and Their Impact on Film Uniformity
The majority of dip coating quality is influenced by the physical behavior that occurs when the substrate is withdrawn from the solution.
Withdrawal Speed: Key Determinant of Film Thickness
Film thickness in dip coating is primarily governed by withdrawal speed. Physically, thickness is proportional to a power of the withdrawal speed, meaning faster speeds result in thicker films. Therefore, the withdrawal speed must be set precisely according to the target thickness and kept constant.
When controlling film thickness at the micrometer level, even slight variations in motor rotation or mechanical vibration can directly cause coating unevenness. Selecting a highly stable and precise withdrawal system is therefore the first requirement for high-quality coating.
Process Design for Dipping and Withdrawal to Ensure Coating Quality
Achieving uniform coating requires careful attention not only during withdrawal but also before and after this stage.
During immersion, the substrate should enter the solution vertically and at a low speed to avoid air entrapment. Air bubbles adhering to the surface cause defects such as pinholes.
Before starting withdrawal, allow a dwell period where the substrate remains fully submerged. This helps ensure proper wetting and prevents film breaks or repulsion during withdrawal.
Environmental vibration or airflow may cause ripples on the liquid surface, leading to waviness or pooling during drainage. A stable and disturbance-free environment is essential.
Substrate Pre-Treatment and Its Impact on Final Film Quality
Even the best equipment and coating solution cannot yield a good film if the substrate surface is improperly prepared. Contaminants such as fingerprints or fine dust significantly impair adhesion and wetting. Cleaning with alcohol or similar agents immediately before coating is fundamental.
Some substrates, particularly certain plastics or metals, naturally exhibit poor affinity with the coating liquid. For these low-adhesion materials, surface modification technologies such as plasma treatment or UV-ozone processing can be applied to increase surface energy and improve wetting.
Optimizing Solution and Environmental Conditions for Stable Insulation Performance
In addition to process conditions, the coating solution itself and the surrounding environment must also be controlled. These factors are essential for maintaining final insulation performance and ensuring stable production.
Selecting Materials Based on Required Properties and Adjusting Viscosity
The required characteristics of insulation films span a wide range, including heat resistance, moisture resistance, flexibility, and chemical resistance. Depending on these requirements, the primary resin must be appropriately selected from epoxy, urethane, silicone and similar types.
The selected material is then diluted with a solvent and adjusted to an optimal viscosity range to control film thickness. Viscosity is one of the most critical parameters alongside withdrawal speed. If it is too high, liquid does not flow off sufficiently and thicker films are likely to form. If it is too low, the target thickness cannot be achieved.
The drying rate of the solvent, determined by its boiling point, also affects potential defects such as cracking during the later drying stage. Therefore, the final viscosity should be set by considering overall balance.
Designing the Drying and Curing Profile to Prevent Film Defects
The drying and curing stage following dipping is critical, as it converts the liquid film into a functional solid layer. It is important to avoid rapid drying. Sudden heating causes only the surface layer to solidify quickly, and solvent remaining inside may break through the film during evaporation. This may lead to pinholes. Additionally, shrinkage stress can cause cracks or whitening.
To prevent these issues, it is standard practice to design a gradual temperature profile, such as pre-drying at a low temperature followed by final curing. Filter management and clean working conditions are also essential, as fine contaminants mixed into the solution can cause pinholes. For heat-curing systems, the specified temperature and duration must be followed to ensure complete curing and maximize the material’s dielectric breakdown strength.
Solution Control and Environmental Management to Improve Productivity
Unlike the development stage, mass production requires long-term continuous operation. During operation, the coating solution is kept in an open tank where solvent evaporation gradually increases viscosity. Since viscosity variation directly causes thickness fluctuation, it is important to install an automatic viscosity control unit and use a chiller to maintain constant liquid temperature. External temperature and humidity also affect solvent evaporation speed and may lead to quality variation.
To consistently supply high-precision insulation films, it is ideal to perform the entire process in a cleanroom controlled at constant temperature and humidity.
Summary
Dip coating for insulation film formation is a process in which multiple factors, such as withdrawal speed, solution viscosity, and drying conditions, interact in complex ways. Optimizing only one parameter is insufficient. It is essential to understand how these parameters influence each other and maintain overall balance.
The most reliable approach to achieving stable production and high reliability is to precisely record and manage each condition and establish the optimal parameters for your products through repeated PDCA cycles of prototyping and evaluation.
We develop, rent, and provide contract dip coating services using equipment designed with safety in mind. Please feel free to contact us for further consultation.