What Is Dry Film Lamination Process?

The process of dry film lamination involves applying pressure, along with heating, to firmly adhere a polymer dry film to a substrate or surface of a microstructure, resulting in a multilayer formation or the final encapsulation of the device. What follows is an in-depth overview covering the process principle, various application scenarios, benefits, and principal operational aspects:
Principle of Process: Typically, dry film is made up of three distinct layers: a polyester coating (PET, serving as the external protective layer), a photoresist coating (the central layer, the core substance, responsive to certain ultraviolet light wavelengths; areas not exposed dissolve in the developer, whereas those exposed experience a cross-linking reaction leading to insolubility), and a polyethylene safeguarding layer (PE, the innermost layer, touches the substrate during lamination, and is eliminated before or during lamination). During the lamination procedure, a dry film laminator, like a Roller Laminator, is employed. Initially, the protective polyethylene layer of the dry film, when rolled, is removed. Subsequently, in a vacuum environment, hot rollers apply the dry film to a pristine, finely etched, and textured copper base, employing precise temperatures (usually between 100-130°C to soften the adhesive), pressures (ranging from 0.4-0.8 MPa to prevent air bubbles), and velocities (1.5-3 m/min, with adjustments based on the equipment). Swift cooling subsequently enables the dry layer to solidify and adhere.
Application Scenarios: PCB (Printed Circuit Board) Production: Dry film lamination is most commonly used in this field. Within the realm of PCB production, this procedure plays a pivotal role in transferring patterns. Applying a photosensitive dry layer to a pristine copper foil base sets the stage for further exposure, development, and various patterning processes. Serving temporarily as a "protective layer," the dry film guarantees that etching or electroplating impacts only the regions needed for the design. As an illustration, this method finds application in creating high-density interconnect (HDI) boards for smartphone motherboards and 5G modules, and also in constructing multilayer boards and packaging materials (specifically ultra-fine circuits needed for chip packaging, where linewidths ≤10μm demand sophisticated techniques).
Production of Microfluidic chips: Abgrall and colleagues in 2005 crafted a production method for 3D microfluidic networks, entirely composed of SU-8 and incorporating electrodes. The outlined method facilitates the creation of unlinked SU-8 dry films on polyester (PET) sheets, followed by lamination to produce closed microstructures, showcasing the complete dry release of polymer microstructures and the creation of pliable microfluidic chips. The method employs basic instruments and eschews the use of wafer bonding devices, opting instead for a more focused lamination approach.
Benefits and Characteristics: Superior accuracy: The consistent thickness of dry films significantly influences the accuracy of etching; typical thicknesses range from 15-40μm, fulfilling the stringent precision demands of PCB production and various other uses.Additionally, through the fine-tuning of process parameters, it's possible to attain ultra-thin dry films (less than 10μm) for HDI fine lines.Concurrently, the integration of laser direct imaging (LDI) technology with dry film lamination diminishes errors in films, thereby enhancing the precision of pattern transfer.
Stable Quality: The dry film demonstrates robust attachment to the substrate under appropriate processing conditions, successfully clearing tape tests and averting peeling in its development phase.Additionally, the lamination procedure takes place in a vacuum setting, thereby averting the creation of bubbles, maintaining consistent lamination integrity, and mitigating issues like inadequate exposure due to bubbles.
Beneficial to the Environment: Dry film lamination, in contrast to wet film methods, obviates the necessity for extensive organic solvents in coating and drying, thereby lowering volatile organic compound (VOC) emissions and enhancing its environmental friendliness.
Essential Points of Operation:
Preparation of the Substrate: It necessitates thorough cleaning processes such as chemical cleansing, brushing, sandblasting, and more.and the process of micro-etching is employed to eliminate oxide layers, oil, and dust from the surface of copper foil, followed by proper roughening to markedly enhance the bond between the dry film and the copper foil.
Control of Parameters: It's crucial to precisely fine-tune process variables (like temperature, pressure, speed) to suit the size of the substrate and the type of dry film.High temperatures, for instance, can lead to wrinkling, bubble formation, thinning in certain regions, and diminished adhesion from over-drying of the dry film; conversely, very low temperatures can cause reduced adhesion and lower filling capacity.The bond between the dry film and substrate is impacted by fluctuating pressure, and the presence of gaps or scratches on the pressure rollers also influences the adhesion between the board surface and the dry film adhesive.
Specifications for the Environment: To prevent dust and impurities from impacting lamination quality, the operating area is required to adhere to cleanroom norms (Class 100K or lower).Concurrently, it's essential to keep the dry film in a cool and uncontaminated indoor setting, steering clear of chemical and radioactive storage.The conditions for storage encompass a zone bathed in yellow light, temperatures under 27°C (with 5-21°C being the ideal range), and humidity levels near 50%.The product's usability must be limited to a maximum of six months post-production; however, films that clear inspection post-production are still viable.