Jet Dispensing Non-Contact Type

Jet dispensing, also known as jetting, is a direct-dispensing process whereby the adhesive paste is forced through afine nozzle and programmed to flow onto selected areas controlled fi om a computer database. It is an automated method that differs fi om syringe/needle dispensing in that contact with the surface is not required to produce the dots, lines, or patterns. 

Adhesives for jet dispensing must have relatively low viscosities of approximately 120,000 cps at 5 rpm, or20,000-40,000 cps at 10 rpm, and last recovery of thixotropic properties after dispensing (narrow hysteresis in viscosity loop). Examples of SMT adhesives that are jet dispensible are Loctite s Chipbonder 3621, Epoxy Technology s Epo-Tek H70E, and Emerson Cuming s Amicon E-1330.1 1 

Preforms, tape, or film adhesives, unlike the paste or liquid adhesives, are already in the solid state. They may be thermoplastic or thermosetting but, in both cases, may be purchased as sheets of various thicknesses and cut to size to accommodate specific device or part sizes. In using preforms, the electronics assembler avoids problems associated with the storage, handling, and dispensing of liquid adhesives. Parts such as leadframes, lids, and substrates may also be purchased with pre-attached preforms, a convenience to the user, who then avoids having to cut and handle individual preforms. Most parts can also be stored for up to one year in ambient conditions without affecting their properties. 

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