Screen Printing Of Ceramic Substrate
Screen printing is a way to produce a desire pattern that material deposition onto a surface by forcing ink via a fine mesh screen. It is suitable for printing on different types of surfaces. In screen printing equipment, ink is spread across a patterned mask using a screen print squeegee and transferred onto the substrate to create the required pattern. According to purpose, the substrate and screen mesh consist of metal, plastic, cloth and any other material. Screen printing (SP) process excellent properties of cost effectiveness and simplicity. The electronic circuit board use SP technology for massive production. Screen printing apply in thick film measurement and electronic circuitry widely. In integrated circuit industry, thin film deposition is one of the main methods used to produce a wide range of devices. By this way, SMD are attach on ceramic PCB.
Screen Printing Process
Screen printing is a technique used to print patterns on surfaces. This is done by forcing material through a mesh screen onto the surface using a squeegee. The quality of the print is affected by things like the pressure and speed of the squeegee. The screen is stretched on a frame so it does not move or get damaged. The screen is first coated with an ink that can be cured with light. A pattern is then applied to the screen and cured. This makes some areas of the screen open and others closed[1]. The screen is then put over the surface and ink is applied. The squeegee is used to push the ink through the areas of the screen and onto the surface. This makes the pattern on the surface. The squeegee is very important. Must be handled carefully. The surface must also be smooth so the pattern sticks well. After printing the screen must be cleaned so it does not get damaged.
Materials Used in Screen Printing
Ceramic PCB screen printing process begins with blank substrate preparation, which used a CO₂laser to realize. Then, the screen-printing process is ready to build the layered structure. First, the bottom electrode is printed, dried, and fired using a standard thick-film gold conductor. A multi layer insulation deposited over the electrode to provide protection to against chemical etching. Next, a sacrificial layer is applied via a thick-film gold material. Finally, the top dielectric and top electrode layers are printed on the substrate and undergo a die cutting process. The film thickness measurement is restricted to about 20 μm [2]. Metal based thermal paste are widely applied in conductive printing components for sensors and electronics. For glass substrate, lower densification temperatures are required. Although low-melting glass frite binders are used. Subtractive patterning techniques can be applied to materials in ceramics. Which include alumina (Al₂O₃), beryllia (BeO), aluminum nitride (AlN), sapphire, and fused silica. However, due to their inherent limitations, these methods are not well suited for fabricating microstructures[3].
Key Parameters Affecting Print Quality
Screen printing is a way to produce a desire pattern that material deposition onto a surface by forcing ink via a fine mesh screen. It is suitable for printing on different types of surfaces. In screen printing equipment, ink is spread across a patterned mask using a screen print squeegee and transferred onto the substrate to create the required pattern. According to purpose, the substrate and screen mesh consist of metal, plastic, cloth and any other material. Screen printing (SP) process excellent properties of cost effectiveness and simplicity. The electronic circuit board use SP technology for massive production. Screen printing apply in thick film measurement and electronic circuitry widely. In integrated circuit industry, thin film deposition is one of the main methods used to produce a wide range of devices. By this way, SMD are attach on ceramic PCB. while conductive layers and connections can also support applications such as metal bonding in power electronic modules.
Process
The desire print quality need to realize by process parameters. During screen printing, a wedge of paste between the squeegee and screen generates hydrodynamic pressure. The volume of paste passing through the screen depends on the generated pressure, which is affected by squeegee angle, pressure zone length, squeegee speed, paste viscosity, and screen pore radius. In addition, screen specifications and ink system ingredients also have influence on print quality. The ink film thickness is the main element. , since thin coatings may reduce pattern visibility and conductivity for subsequent solder connection. When a constant volume of ink is distributed over a larger area, the resulting film thickness decreases compared to deposition over a smaller area. Thus, expect ink amount transferred on the substrate, the integrity of deposited ink is also crucial. Mesh count is an important parameter affecting the thickness of printed films. Mesh count is the number of threads or openings per inc, which can further affect later manufacturing steps such as etching pattern formation and circuit fabrication. Another key factor affecting print quality is the open area percentage, which can be expressed as:
Open area (%) = (1 − mesh count × wire diameter)² × 100%, where both parameters are in inches. For example, a 325-mesh screen with a wire diameter of 0.0011 inches (0.028 mm) has an open area of about 41%. A higher open area generally leads to better resolution. In addition, the weave type of the screen—such as plain, twill, or other patterns involving warp and weft—also influences the printed thickness. Screen tension and wire alignment are further critical parameters. Screen tension, measured in N/cm, indicates how tightly the mesh is stretched and plays an important role in ink release. Proper tension improves printing performance, while excessive tension makes it difficult to maintain the snap-off distance and may cause permanent damage if the yield point is exceeded. On the other hand, insufficient tension can lead to poor ink transfer and separation issues.
Squeegee selection is crucial for achieving fine-line printing. Rough or uneven surfaces, as well as low screen printing mesh count, typically require softer squeegees with a durometer of 60–70 Shore A. Softer squeegees are also suitable for depositing thicker ink layers, especially when printing at lower speeds and with reduced pressure. Choosing the right squeegee durometer depends on both the printing conditions and properties of surface tension. Certain printing application decide squeegee profiles[4]. The round edge profile is suit for precision textile. Beveled edge profiles are optimized for high-resolution printing on curved surface and are particularly effective in high-speed processes. For printed batteries, square edge profiles are preferred due to their ability to achieve a good balance between film thickness, adhesion, and overall print quality.
Advantages of Screen Printing
Screen printing has numerous merits, including cost effectiveness, disposability, reproducibility. For large scale and rapid production of printed microelectronics, forming competitive solution for economical sensors. By enabling printing on substrates like ceramics, plastics, and paper, this technique offers versatile material compatibility and adaptable electrode design. Screen printing can form for sequential film deposition. It can be used to fabricate all layers, or integrated with other processing methods to deposit selected layers in a multilayer structure. This method is used for solar cell production.
Limitations of Screen Printing
Screen clogging
Clogging can occur due to high paste viscosity, poor squeegee design, insufficient cleaning, or residue buildup on the screen. Frequent interruptions during printing can also contribute to this problem.
Air bubbles in printed films
Air bubbles often result from high-viscosity inks or excessive mixing speed. Allowing time for bubbles to settle and adjusting mixing conditions can help reduce them. High printing speeds may also introduce bubbles, which can be minimized by lowering the squeegee speed.
Contamination
Foreign particles in the ink or on the screen can lead to defects such as blank spots or uneven ink deposition. Dust and lint may also cause excessive ink buildup. Maintaining a clean working environment and properly cleaning the screen are essential to avoid contamination.
Leakage, bleeding, and pinholes
Surface contamination of the substrate can cause ink smearing or pinholes, especially in non-image areas. These issues can be reduced by cleaning the substrate, avoiding direct handling, and sealing non-printing regions. Ink bleeding around patterns may also occur due to contamination beneath the stencil.
Ink spreading
Excessive pressure during the flood or printing stage can cause the ink to spread beyond the desired pattern, leading to thicker prints and irregular edges. Proper control of squeegee pressure and maintaining an appropriate edge profile can help limit this effect.
Blurred or ghosted edges
Electrostatic forces between the screen, squeegee, and substrate may cause double edge or blurred pattern. This can be mitigated by grounding the equipment and using anti-static additives in the ink.
