John we paced through the same question recently.
Both automatic dispensers and printers can be used to deposit SMT adhesive or solder paste on substrates with a relatively high component density. Dispensers are superior to printers in terms of exact positioning and precise deposit volume control. New generation automatic dispensers can be re-programmed for a new product much faster than a printer can be setup. Dispensers do not require the lost time in developing a stencil for new or changed products. If the purchase decision is strictly based on capital, buyers generally choose printers over dispensers. A further comparison of dispensers and printers follows.
Factor|Dispenser|Printer || Solder paste waste (%)|4|30 Operator concerns|Very clean, no mess|Paste is messy |Straight forward machine clean-up|Stencil cleaning capability required ||Waste disposal requirements similar to other activities Deposition control|High control over amount paste|Difficult to control amount of paste ||Stepped stencils can be a nightmare ||Stencil apertures clog with paste |Coplaniarilty issues controllable|Coplaniarity issues make printing difficult |Paste rheology does not play a large role in dispensing|Rheology requires constant working of paste |Requires process control to prevent missing dots|Requires process control to prevent misprints, clogged apertures Flexibility|Allows frequent design changes|Stencil(s) required for each production stage Material handling|Nozzles require cleaning|Stencil cleaning capability required ||Stencils must be stored, maintained, and controlled Change-over time between products |Quick as loading another program|Stencil, vision system, printer, and substrate must be aligned Change over time between materials |Quick as loading another program|Stencil, vision system, printer, and substrate must be aligned |Change syringe and purge|Requires cleaned-up of previous material Solder paste cost|Expensive -400 to +500 mesh, negated somewhat by less waste|Less expensive New or revised product start-up|Couple of hours for programming|Hour plus to reduce and adjust apertures, create Gerbers, liaise with suppliers, write purchase orders la di da etc etc ||Stencil foils required for each side and version of product Specialized knowledge|Requires special knowledge to program machine|Operators without special skills can setup machine Speed|Slower, may loose 70% of tact on fast chip shooters|Can be put in front of and use fast chip shooters effectively
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