Thermoset molding compound

The term amino resin is usually appHed to the broad class of materials regardless of appHcation, whereas the term aminoplast or sometimes amino plastic is more commonly appHed to thermosetting molding compounds based on amino resins. Amino plastics and resins have been in use since the 1920s. Compared to other segments of the plastics industry, they are mature products, and their growth rate is only about half of that of the plastics industry as a whole. They account for about 3% of the United States plastics and resins production. 

This paper reports the results of a molecular-level investigation of the effects of flame retardant additives on the thermal dedompositlon of thermoset molding compounds used for encapsulation of IC devices, and their implications to the reliability of devices in molded plastic packages. In particular, semiconductor grade novolac epoxy and silicone-epoxy based resins and an electrical grade novolac epoxy formulation are compared. This work is an extension of a previous study of an epoxy encapsulant to flame retarded and non-flame retarded sample pairs of novolac epoxy and silicone-epoxy compounds. The results of this work are correlated with separate studies on device aglng2>3, where appropriate. 

The most common and widely used thermoset molding compounds are classified as follows (a) alkyd, (b) allylic (diallyl phthalate), (c) amino (melamine and urea), (d) epoxy, (e) phenolic, (f) polyester, and (g) silicone. There may be other specialty thermoset resin materials used on specific applications. 

Being man-made, thermoset molding compounds may be processed, using various fillers, to give most any property desired in an end product. The basic resin itself will impart certain desirable results when compounded with fillers, which will produce an end product that may have superior electrical, physical, and heat resistant characteristics, etc. 

As stated, the basic resin system makes it possible to process a recommended molding compound for a specific end use or application. The general physical, electrical, specific properties, and their applications, may more clearly be understood if each type thermoset molding compound is examined. 

Thermoset molding compounds, when contained within a hardened steel mold, require heat and pressure to be polymerized into a solid mass. Molds may be heated by steam, electricity, or hot oil to temperatures of 280° to 425°F, depending entirely on the type of material and method of molding. Molding pressures may vary from a low of 50 p.s.i. to 15,000 p.s.i. Epoxy materials will mold at 50 p.s.i. whereas, phenolic fabric-filled material may require excessive pressures. Again, the method of molding dictates molding pressures. 

The time required to cure the materials is dependent entirely on the method of molding, mold temperature, and material temperature when introduced into the mold cavity. There are now four basic methods of molding thermoset molding compounds (1) Compression, (2) Transfer, (3) Injection, and (4) Extrusion—with the method most commonly used as rated. Very small quantities are processed by extrusion. All methods of molding may be done automatically or semi-automatically. In most cases, the injection method is practically all done automatically. 

ASTMD3123, Thermosetting Molding Compounds, Spiral Flow, Low Pressure, Vol. 8.02, ASTM, Philadelphia, Pa., 1994. 

ALLYL ESTER RESINS. The allyl radical (CH2CH=CH2) is the basis of the allyl family of resins. Allyl esters arc based on monobasic and dibasic acids and are available as low-viscosity monomers and thermoplastic prepolymers. They are used as crosslinking agents for unsaluraied polyester resins and in the preparation of reinforced thermoset molding compounds and high-performance transparent articles. All modem thermoset techniques may be used for processing allyl resins. 

The most widely used allyls are the monomers and prepolymers of diallyl phlhalate and diallyl isophlhalate. These are readily converted into thermoset molding compounds and into preimpregnated glass cloths and papers. 

Chemical resistance of thermoset-molded compounds used in the manufacture of molded fittings... 

On the other heind, the linear unsaturated polyester resins find use in memy commercial applications, such as in producing solventless lacquers, and thermosetting molding compounds. The resin is normally prepcured by the reaction of a saturated diol with a mixture of an unsaturated dibasic acid and a modifying dibasic acid or its corresponding anhydride. It is commonly referred to as... 

Materials now known as WPCs first appeared as thermosetting molding compounds in the 1960s. Other thermosetting wood composites had appeared much earlier (see below). This section provides a brief look at the development of WPC for the last 40 years or so, not pretending to quote all relevant patents and publications. I would restrict the consideration only by U.S. (and occasionally other) patents, citing the most significant (to my personal viewpoint) developments. 

The hrst WPC—in the 1960s—were thermosetting molding compounds containing cellulose hber as hller. 

ASTM D5224-93, Practice for compression molding test specimens of thermosetting molding compounds, American Society for Testing Materials Publication, Philadelphia, 1992. 

ASTM D3123-94. Spiral flow of low-pressure thermosetting molding compounds. 

Thermosetting Molding Compounds Semiflexible high-bond diixoh opic 78.7 6... 

Thermosetting molding compounds contain fillers or fibrous reinforcements, often as high in content as 50-75% of the total compound weight. These materials... 

Adherent Technologies Inc. [8] has developed a process for the reclamation of carbon fibers from carbon/epoxy composites. It has studied the depolymerization of thermoset carbon fiber reinforced epoxy matrix composites using a low temperature (20 min at 325°Q catalytic tertiary recycling reclamation process and has been able to obtain a product with 99.8% carbon and 0.2% residual resin, with only a loss of about 8.6% in fiber tensile strength. The process can be economically viable, provided sufficient scrap feedstock is available. Possible applications for the recovered fiber include thermoplastic and thermoset molding compounds. 

Calcium silicate (1888) (wollastonite) n. CaSiOs. A naturally occurring mineral found in metamorphic rocks, used as a reinforcing filler in low-density polyethylene, polyester, and other thermosetting molding compounds. It imparts smooth molded surfaces and low water absorption. 

Brabender plasticorder. The plasticorder is a small mixer capable of measuring the viscosity and the gel time of thermosetting molding compounds with results that can be correlated to the performance of a compound during molding conditions. 

Flow specifications. Generally identified as stiff, medium, or soft or by a designated cure rate or flow time. All thermosetting molding compounds possess flow characteristics that are both measurable and controllable with the important characteristics being the rate of curing, speed of the flow, distance of the flow, and finally the amount of compound used during the flow time. 

Figure 6.10 Schematic diagram of screw preplasticizer for preheating thermosetting molding compounds before molding. Preplasticizer may be integrated with molding press for fiilly automatic molding.

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