TABLE OF CONTENTS Adhesive dispensing methods consist of either mass-transfer or selective dispensing. Stencil printing, screen printing, pin transfer, daub transfer, and stamping are examples of mass-transfer types. They are also referred to as tooling-related processes since hard tooling such as stencils and screens are required. In comparison, selective-dispensing methods are computer data driven, such as automated syringe or needle dispensing and jetting processes. Automated dispensing, currently used in over 80% of all production processes,[28] is a continuous process where individual adhesive dots, lines, or patterns are deposited in selected areas of an interconnect substrate using pressurized syringes or pumps. The main advantage of the data-driven processes is flexibility, accommodating a large variety of printed-circuit board types, configurations, and design changes. Selective dispensing is also the only method that can be used once components have been assembled onto a board since it does not require a flat surface as does screen or stencil printing.
Screen printing of conductive and insulative adhesives has been used for decades in the assembly of hybrid microcircuit and multichip modules. Since screen-printing processes are also used to deposit thick-film conductors, resistors, and dielectrics, the processes are fully compatible and cost effective in the production of hybrid microcircuits. Screen printing and stencil printing are both batch processes that are usually less expensive and faster than selective dispensing for large production runs where few changeovers are expected. As an example, 1,000 dots can be stencil printed in 30 seconds compared to 1.5 minutes for a selective dispenser...
