072
ELECTRONICS
Micro dispensing systems for the electronics industry Micro dispensing enables state-of-the-art manufacturing processes in the electronics industry and increases the service life of individual components. Adhesives, sealants, potting compounds or heat conductive pastes are processed in various applications. In consumer electronics in particular, the prerequisites for performance are increasing with ever- smaller components and simultaneously falling manufacturing costs. Fully automatic and process-reliable micro dispensing systems make this possible. For example, in the manufacture of smartphones, components are bonded, potted, and sealed in fully automated micro dispensing systems. A camera in a smartphone has up to 40 different bonding and dispensing applications. Micro dispensing comprises various processes: • In Bonding applications, dispensing systems must be able to provide absolute stable dispensing. On the one hand, the bond must withstand external environmental influences such as high temperature fluctuations, vibrations, or moisture. On the other hand, adhesive residues on the edges or overflowing adhesives between two assembled parts are not acceptable. It is important not to apply too much or too little adhesive: in most applications, a precisely defined amount of material is required without pulling the thread of the material. Adhesive residues can otherwise cause great damage, for instance, due to contamination during production. Moreover, a quantity too small would impair the adhesive strength. • In Dam & Fill applications, a highly viscous barrier, the socalled “dam” in the form of a closed outer contour, is first applied to the surface to be sealed. The internal area is then filled with a low-viscosity sealing compound. Both materials are then cured together. The area to be protected is thus sealed and optimally shielded against external influences. The primary goal is to protect the highly complex and sensitive assemblies. • Glob Top potting protects sensitive components, usually semiconductor chips, from mechanical stress such as vibrations or temperature fluctuations. And it also protects them from external environmental influences such as moisture or corrosion. Simultaneously to Dam & Fill, a liquid resin matrix usually based on epoxy resin is applied, whereby the dam can be eliminated. • Classic Underfill applications are primarily used to mechanically stabilise various components on printed circuit boards while at the same time compensating for different thermal expansions. In this way, damage due to stress is avoided. As a rule, the adhesives used in this process display a very high capillary flow behaviour and thus completely fill the gap between the chip and the printed circuit board (PCB), though the adhesive is only dosed along the outer contour of the chip. • Micro dispensing means that the dosing volume is in the range of 0.001ml. Whether bead dosing, sealing, point dosing, potting or two-component applications, precision, repeatability and reliability are essential. ViscoTec dosing systems, for example, process low- to high-viscosity liquids and pastes with a repeat accuracy of higher than 99 %. The repeat accuracy depends both on the dosing process and the material properties. • Encapsulation means that an electronic potting compound is applied to a predetermined surface. It protects the component during transport and against external influences such as vibrations, shocks, moisture, dust, and extreme temperatures. The joint not only protects, but also improves electrical insulation, protection against damage and chemical resistance.
AMT JUN/JUL 2021
• Optical Bonding eliminates the gap between the glass and display of smartphones and tablets, reducing the effect of different refraction and reflection. In addition, the stability and damage resistance of the display is increased. The main goal is to improve readability of the displays outdoors. • Conformal Coating, for example, protects PCBs from moisture, contamination with dust or chemicals or temperature fluctuations. In addition, reliability and electrical properties can also be improved. The automated application of various viscous materials is intended to offer maximum flexibility in the selection of the suitable dosing material on the one hand and to enable uncomplicated processing through maximum reliability on the other. There are several important parameters that determine the dosing process. Short cycle times, cyclical application, or continuous operation, low to highly viscous, structure-sensitive, solids-laden liquids, tribological losses such as friction, leaks, wear, aging, fracture mechanics. The suitable dosing pump takes all variables into account and is adapted to the material. In addition, chemical reactions can occur that lead to wear, such as plastic deformation, abrasion, static friction, and fracture mechanics. For the optimal design of the dosing components for abrasive or chemically aggressive liquids, special know-how is required. In addition, it is often necessary to carry out preliminary or long-term testing. How should the dosing system be designed so that highly viscous, abrasive and shear-sensitive liquids can be reliably processed? And at the same time changes in the flow behaviour of these liquids be tolerated? The progressive cavity pump technology combines both: long maintenance intervals due to optimum pump assembly, and absolute low-shear and viscosity-independent conveying of the material. Metering pumps based on this principle, the so-called endless piston principle, achieve a long service life and very high energy efficiency.
