Thermoplastic rework

The thermoplastic or thermoset nature of the resin in the colorant—resin matrix is also important. For thermoplastics, the polymerisation reaction is completed, the materials are processed at or close to their melting points, and scrap may be reground and remolded, eg, polyethylene, propjiene, poly(vinyl chloride), acetal resins (qv), acryhcs, ABS, nylons, ceUulosics, and polystyrene (see Olefin polymers Vinyl polymers Acrylic ester polymers Polyamides Cellulose ESTERS Styrene polymers). In the case of thermoset resins, the chemical reaction is only partially complete when the colorants are added and is concluded when the resin is molded. The result is a nonmeltable cross-linked resin that caimot be reworked, eg, epoxy resins (qv), urea—formaldehyde, melamine—formaldehyde, phenoHcs, and thermoset polyesters (qv) (see Amino resins and plastics Phenolic resins). 

Polyurethanes for their thermoplastic properties, ease of rework, flexibility, vibration damping, and stress dissipation. 

Polyurethane adhesives are used primarily in the assembly of printed-wiring boards to attach large components such as capacitors, magnetics, heat sinks, and connectors. Their key benefits include flexibility, absorption of stresses, vibration damping, and thermal transfer. Being thermoplastic, polyurethanes are also easier to rework than epoxies. 

Hybrid microcircuits and MCMs MIL-STD-883, Method 5011-compliant, low outgassing, high-purity, reworkability Silver-filled or insulative epoxies, thermoset or thermoplastic pastes or films... 

Thermoplastic hot melt adhesives have also found use in flat-panel displays (FPDs) because of their rapid bonding and ease of reworking. 

The basic difference between thermoset and thermoplastic resins is the reaction heat. A thermoset resin is cured by the application of heat and often by the addition chemicals called curing agents. Once cured, the material is infusible, unsoluble and can softened or reworked with the addition of heat. 

Reworked material n. A thermoplastic from a processor s own production that has been reground, pelletized, or solvated, after having been previously processed by molding, extrusion, etc. Note—In many specifications... 

Both thermoplastic and thermoset resins can be used for ICA formulations. The main thermoplastic resin used for ICA formulations is polsrimide resin. An attractive advantage of thermoplastic ICAs is that they are reworkable, eg, can... 

Thermoplastic materials have curing temperatures that are lower and time durations that are shorter than thermosetting materials. Some compositions will cure at room temperature, making them suitable for temperature-sensitive components or when thermal expansion mismatch, residual stresses are of concern. Another advantage of thermoplastic adhesives is that because they readily soften at elevated temperatures, they can be easily removed to allow for the rework of components. 

Reworked Material n A thermoplastic from a processor s own production that has been reground, pelletized, or solvated, after having been previously processed by molding, extrusion, etc. NOTE — In many specifications the use of reworked material is limited to clean plastic that meets the requirements specified for the virgin material, and yields a product essentially equal in quality to one made from only virgin material (ASTM D 883). See also Regrind. 

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