ENCAPSULATING COMPOSITIONS

Abstract: Encapsulating compositions are prepared from reinforced polyaromatic cyanates compositions comprising (A) one or more polyaromatic cyanates at least one of which is a hydrocarbon polyaromatic cyanate resin such as a phenol-dicyclopentadiene novolac polycyanate and (B) one or more curing agents such as cobalt naphthenate. These compositions are particularly suitable for use in electrical applications such as the encapsulation and subsequent protection of electrical and micro electronic devices and circuitry.

Description: ENCAPSU ATING COMPOSITIONS Encapsulating compositions have previously been prepared from epoxy resins such as phenol-aldehyde epoxy resins, cresol-aldehyde epoxy resins, bisphenol A epoxy resins, and the like. Encapsulating compositions have likewise been prepared from bisphenol A cyanates. However, while these epoxy resins and bisphenol A cyanates result in encapsulating compositions suitable for use in encapsulating electrical and electronic components, it would be desirable if such compositions had an improvement in one or more of its properties. It has now been discovered that the present invention provides an improvement in one or more of the following: moisture resistance, thermal cycling character¬ istics and resistance to thermal shock, elevated tempera- ture electrical properties, retention of physical thermal electrical and chemical resistant properties after moisture exposure. The present invention concerns encapsu¬ lating compositions comprising (A) at least one polyaromatic cyanate; and optionally (B) one or more catalysts to aid in the curing of component (A); characterized by employing as at least a part of com¬ ponent (A) at least one hydrocarbon polyaromatic cyanate resin in an amount such that at least 40, preferably from 90 to 100 percent of the cyanate groups present in component (A) are contributed by said hydrocarbon polyaromatic cyanate novolac resin. In the preferred embodiment the present invention concerns an encapsulating composition which comprises in addition to components (A) and (B), a filler material (C) wherein (i) component (A) is the product resulting from cyanating (1) a hydrocarbon novolac resin, (2) a halogenated hydrocarbon novolac resin, (3) a combination of (1) and (2) or (4) a combination of (1), (2) or (3) and a phenol-aldehyde cyanate resin, a bisphenol A cyanate resin, a halogenated phenol-aldehyde cyanate resin, a halogenated bisphenol A cyanate resin or a combination thereof; (ii) component (B) is a cobalt salt; (iii) component (C) is present in an amount of from 50 to 80 percent by weight of the combined weigh of components (A),. (B) and (C); and (iv) said hydrocarbon polyaromatic cyanate resin or halogenated hydrocarbon poly¬ aromatic cyanate resin is present in an amount such that from 90 to 100 percent of the cyanate groups present in com¬ ponent (A) are contributed by said hydrocarbon polyaromatic cyanate or halogenated hydrocarbon polyaromatic cyanate resins or a combination of such resins. In another preferred embodiment this inven¬ tion concerns an encapsulating composition wherein (i) component (A) contains the product resulting from cyanating the product resulting from reacting phenol, cresol or a combination thereof with an unsat- urated hydrocarbon containing an average of from 6 to 55 carbon atoms per molecule or halogenated derivatives of such reaction products, or mixture of such hydrocarbons or halogenated derivatives thereof; (ii) component (B) is cobalt naphthenate, cobalt acetylacetonate or cobalt octo- ate; and (iii) component (C) is silica flour. In still another preferred embodiment this invention concerns an encapsulating composition wherein (i) component (A) contains (a) the product resulting from cya¬ nating the reaction product of phenol, cresol or a combination thereof with a composition com¬ prising from 70 to 100 percent by weight of dicyclopentadiene, from zero to 30 percent by weight of C 9 -C 12 dimers of C -C 6 dienes, from zero to 7 percent by weight of oligomers of C -C 6 unsaturated hydrocarbons and the balance, if any, to provide 100 percent by weight of C 4 -C 6 alkanes, alkenes or dienes; (b) halogenated derivatives of the product of component (a); or (c) combinations of components (a) and (b); (ii) component (B) is cobalt naphthenate; and (iii) component (C) is silica flour. In another aspect, this invention concerns an electrical and/or electronic component encapsulated with the above encapsulating composition. The hydrocarbon polyaromatic cyanate resins employed in the present invention can be prepared by reacting cyanogen chloride or cyanogen bromide in a suitable solvent such as a chlorinated hydrocarbon with a hydrocarbon novolac resin dissolved in a suitable solvent in the presence of a tertiary araine at a tem¬ perature of 0°C or below. If desired, the cyanogen chloride can be prepared insit by reacting a solution of chlorine in a chlorinated hydrocarbon with an aqueous solution of an alkali metal cyanate at a temperature of 0°C or below, separating the chlorinated hydrocarbon in which the cyanogen chloride is dissolved from the aqueous layer in which the alkali metal chloride is dissolved. The cyanogen chloride containing chlori- nated hydrocarbon can then be employed in the above reaction. Suitable hydrocarbon polyphenolic resins which can be reacted with cyanogen chloride or cyanogen bromide to form the hydrocarbon polyaromatic cyanate resins employed herein include those disclosed by -Vegter et al in U.S. Patent 3,536,734, by Nelson in - U.S. Patent 4,390,680 and Nelson et al in U.S. Patent 4,394,497. Particularly suitable hydrocarbon novolac resins include the reaction product of an aromatic hydroxyl-containing compound with an unsaturated hydro¬ carbon having from 4 to 55 carbon atoms. Suitable aromatic hydroxyl-containing com¬ pounds which can be employed include any such compounds which contain one or two aromatic rings, at least one phenolic hydroxyl group and at least one ortho or para ring position with respect to a hydroxyl group available for alkylation. They may also contain substituent hydrocarbon or halogen groups if desired. Particularly suitable aromatic hydroxyl- -containing compounds which can be employed include, for example, phenol, chlorophenol, bromophenol, methyl- phenol, hydroquinone, catechol, resorcinol, guaiacol, pyrogallol, phloroglucinol, isopropylphenol, ethyl- .. phenol, propylphenol, t-butylphenol, isobutylphenol, octylphenol, ' nonylphenol, cumylphenol, p-phenylphenol, o-phenylphenol, m-phenylphenol, bisphenol A, tetra- bromobisphenol A, dihydroxydiphenyl sulfone, and mix¬ tures thereof. Suitable unsaturated hydrocarbons which, either in a crude or purified state, can be employed include, for example, butadiene, isoprene, piperylene, cyclopentadiene, cyclopentene, 2-methylbutene-2, cyclo- hexene, cyclohexadiene, methyl cyclopentadiene, dicyclo¬ pentadiene, limonene, dipentene, linear and cyclic dimers of piperylene, methyl dicyclopentadiene, dimethyl dicyclopentadiene, norbornene, norbornadiene, ethylidine norbornene, and mixtures thereof. Also suitable unsat¬ urated hydrocarbons include the other dimers, codimers, oligomers and cooligomers of the aforementioned unsat- urated hydrocarbons. Particularly suitable unsaturated hydrocarbons which can be employed herein include, for example, a dicyclopentadiene concentrate containing from 70 to 100 percent by weight of dicyclopentadiene; from 0 to 30 percent by weight of C 9 -C 12 dimers or codimers of C 4 -C 6 dienes such as, for example, cyclo- pentadiene-isoprene, cyclopentadienepiperylene, cyclo- pentadiene-methyl cyclopentadiene, and/or dimers of isoprene, piperylene, methyl cyclopentadiene and the like; from zero to 7 percent by weight of C 14 -C 18 trimers of C 4 -C 6 dienes and from zero to 10 percent by weight of aliphatic diolefins such as, for example, piperylene, isoprene, 1,5-hexadiene and cyclic olefins such as cyclopentadiene, methyl cyclopentadiene, and cyclopentene. Methods of preparation for these dicyclopentadiene concentrates and more detailed descriptions thereof can be found collectively in U.S. Patent No. 3,557,239 issued to Gebhart et al and U.S. Patent No. 4,167,542 issued to Nelson. Also, particularly suitable unsaturated hydrocarbons which can be employed include a crude dicyclopentadiene stream containing from about 20 to 99 percent by weight dicyclopentadiene, from zero to 10 percent codimers and dimers of C 4 -C 6 hydrocarbons (described above), from zero to 10 percent oligomers of C 4 -C 6 dienes and the balance to provide 100 percent C 4 -C 6 alkanes, alkenes and dienes. Also, particularly suitable unsaturated hydrocarbons which can be employed herein include a crude piperylene or isoprene stream containing from -30 to 70 percent by weight piperylene or isoprene, zero to ten percent by weight C 9 -C 12 dimers and codimers of C 4 -C 6 dienes, and the balance to provide 100 percent C 4 -C 6 alkanes, alkenes and dienes. Also, particularly suitable are hydrocarbon oligomers prepared by polymerization of the reactive components in the above hydrocarbon streams e.g., dicyclopentadiene concentrate, crude dicyclopentadiene, crude piperylene or isoprene, individually or in com¬ bination with one another or in combination with high purity diene streams. Suitable aromatic polycyanate resins which can be employed herein in combination with the hydro- carbon polyaromatic cyanate resins include, the cyanate derivatives of di- or polyhydroxyl compounds such as, for example, resorcinol, catechol, hydroquinone, bis¬ phenol A, bisphenol F, bisphenol S, phenol or substi¬ tuted phenol/aldehyde resins, tetrabromobisphenol A, and other halogenated phenolic compounds, and com¬ binations thereof. Suitable catalysts which can be employed to cure the polycyanate resins include acids, bases, salts, nitrogen and phosphorus compounds. Particularly suitable catalysts include, for example, Lewis acids such as A1C1 3 , BF 3 , FeCl 3 , TiCl 4 , ZnCl 2 , SnCl 4 ; proton acids such as HC1, H 3 P0 4 ; aromatic hydroxy compounds such as phenol, p-nitrophenol, pyrocatechol, dihydroxy naphthalene, sodium hydroxide, sodium methylate, sodium phenolate, trimethylamine, triethylamine, tributyl- amine, diazobicyclo(2,2,2)octane, quinoline, isoquino- line, tetrahydroisoquinoline, tetraethyl ammonium chloride, pyridine-N-oxide, tributylphosphine, phos- pholine-Δ 3 -l-oxa-l-phenyl, zinc octoate, tin octoate, zinc naphthenate and mixtures thereof. Particularly suitable catalysts include, for example, cobalt naphthenate, cobalt acetylace onate, cobalt octoate, cobalt chloride, 1,4-diazobicyclo- (2,2,2)octane, and combinations thereof. Usually it is desirable to employ one or more filler materials in the encapsulating compositions of the present invention. Suitable filler materials which can be employed herein include, for example, finely divided silica flour, quartz, calcium silicate, barium sulfate, hydrated alumina. Filler selection will have varying effects on moisture permeation through the molded or encapsulated piece since they make up between 50 and 80 percent by weight of the complete composition. If desired, mold release agents can be . employed in the transfer molding compositions of the present invention. Suitable such mold release agents include, for example, stearates such as glycerol mono- stearate, calcium stearate or waxes such as Montan wax or carnauba wax, and combinations thereof. The encapsulating compositions of the present invention are suitable for use in encapsulating elec¬ trical and electronic devices and the like. They are particularly suitable for use in encapsulation of micro circuitry typically found in discrete device and inte- grated circuits. If desired, the composition of the present invention can also contain fire retardant additives and coupling agents. The following examples are illustrative of the invention, but are not to be construed as to limit¬ ing the scope thereof in any manner. Example 1 A. Preparation of Hydrocarbon Polyaromatic Cyanate Resin Into a 1-liter, 3-necked flask with a thermo- well equipped with a mechanical stirrer, metered drop¬ ping funnel, gas dispersion tube and N 2 inlets was added 400 ml CH 2 C1 2 . This was cooled down to -10°C via a dry ice/ethylene glycol/H 2 0 bath. Cl 2 (42.6 g, 0.6 mole) was then added through a dispersion tube to the slowly stirring solution. While the Cl 2 addition was taking place a solution of sodium cyanide (NaCN) (29.4 g, 0.6 mole) in 75 ml H 2 0 was prepared. When the , Cl 2 addition was complete, the dropwise addition of aqueous NaCN was begun at a rate to maintain a temperature of -10°C (approximate rate of addition 1.8 ml/min., 0.03 ml/s). The pH of the aqueous phase was monitored, and NaCN added until slightly alkaline (pH 8,9). The aqueous phase was then separated and discarded. 5 . A solution of hydrocarbon novolac (93.0 g, 0.56 equivalent) in 250 ml CH 2 C1 2 was cobled to ~0°C. This was then added to the CNC1/CH 2 C1 2 previously prepared. Dropwise addition of triethylamine (60.6 g, 0.6 mole) to the stirring (~500 rpm) CNCl/Novolac/- 0 CH 2 C1 2 solution was begun. Addition was at a rate to maintain a temperature of below -10°C (rate ~1.2 ml/- min., 0.02 ml/s). When addition was completed the cooling bath was removed and the contents stirred for 1 hour (3600 s). Then 250 ml H 2 0 were added and the 5 mixture stirred for 5 minutes (300 s). The mixture was transferred to a separatory funnel. The aqueous phase was removed and the organic phase was washed with one 250 ml portion of 0.2N HCl and two 250 ml portions of H 2 0 prior to drying over MgS0 4 . After filtering, the 0 CH 2 C1 2 was removed on a rotating evaporator. B. Preparation of Unfilled Molding Composition To 350 g of the hydrocarbon polyaromatic cyanate resin prepared in A above in the molten state (80°C) was added 0.025 percent by weight of cobalt 5 naphthenate as a 6 percent by weight solution in mineral spirits. The resultant mixture was poured into a 1/8 inch (3.175 mm) thick mold and cured at 175°C for 1 hour (3600 s) and at 225°C for an additional 2 hours (7200 s). The results are given in Tables I, II,. Ill 0 and IV. Comparative Experiment A For comparative purposes, an unfilled molding composition was prepared by blending 400 g of a cresol epoxy novolac resin having an epoxide equivalent weight of 216 and an average functionality of 5.5 with 92.6 g of methylene dianiline. This mixture was poured into a mold as described in Example 1-B and cured for 16 hours (57,600 s) at 55°C, 2 hours (7200 s) at 125°C and 2 hours (7200 s) at 175°C. The results are given in the following Tables I, II, III and IV. ' Comparative Experiment B Also for comparative purposes, a diglycidyl ether of bisphenol A having an epoxide equivalent weight of 189 (400 g) was blended with methylene dianiline (105.8 g) and cured at 55°C for 16 hours (57,600 s) and at 125°C for 2 hours (7200 s) and at 175°C for 2 hours (7200 s). The results are given in Table IV. Ccomparative Experiment C Also for comparative purposes, a polyglycidyl ether of a novolac resin having an epoxide equivalent weight of 179 and an average functionality of 3.6 (400 g) was blended with methylene dianiline (111.7 g) and cured at 55°C for 16 hours (57,600 s) and at 125°C for 2 hours (7200 s) and at 175°C for 2 hours (7200 s). The results are given in Table IV. TABLE I THERMAL PROPERTIES DEGRADATION RESIN Tg a , °C ONSET 13 , °C Example 1 228 423 Comp. Expt. A 227 378 a Tg measured by differential scanning calorimetry (DSC). Ή Samples were heated at 10°C/minute. Degradation onset is defined as temperature at which initial rapid weight loss occurs. TABLE II ELECTRICAL PROPERTIES EXAMPLE COMP. 1 EXPT. A Dissipation Factor, 1000 cps (1 Pa « s) 21 β C 0.0020 0.0125 150°C 0.0047 0.0040 Dielectric constant, 1000 cps (1 Pa*s) 21°C 2.83 4.31 150°C 2.84 4.30 Volume Resistivity (ohm-cm), 500V 21°C >10 16 >10 16 150°C >10 16 1.61 X 10 11 TABLE III MOISTURE WEIGHT GAIN* EXPOSURE TIME % WEIGHT GAIN HOURS/SECONDS EXAMPLE 1 COMP. EXPT. A 25/90,000 0.71 1.85 50/180,000 0.76 2.25 75/270,000 0.83 2.39 100/360,000 0.85 2.51 200/720,000 0.98 2.72 300/1,080,000 1.12 2.88 400/1,440,000 1.25 3.00 500/1,800,000 1.40 3.08 *1 in. x 3 in. x 1/8 in. (25.4 mm x 76.2 mm x 3.175 mm) coupons were exposed for 500 hours (1,800,000 s) to 250°F (121.1°C) and 15 psig (103.4 kPa) steam. TABLE IV EQUILIBRIUM MOISTURE WEIGHT GAIN* WEIGHT GAIN, % Example 1 1.26 Comp. Expt. A 2.73 Corap. Expt. B 1.90 Comp. Expt. C 2.81 *Samples were exposed by submersion in water at 80°C. The exposure times were in excess of 1000 hours (3,600,000 s) allowing all samples to reach an equi¬ librium moisture gain.

Claims: 1. An encapsulating composition comprising (A) at least one polyaromatic cyanate resin; characterized by employing as at least a part of com¬ ponent (A) at least one hydrocarbon polyaromatic cya-. nate resin, halogenated hydrocarbon polyaromatic cya¬ nate resin or a combination thereof in an amount such that 40 percent of the cyanate groups present in com¬ ponent (A) are contributed by said hydrocarbon poly¬ aromatic cyanate resin. 2. An encapsulating composition of Claim 1 comprising in addition to component (A), (B) at least one catalyst to aid in curing component (A); characterized by employing as at least a part of component (A) at least one hydrocarbon polyaro- matic cyanate resin, halogenated hydrocarbon polyaro¬ matic cyanate resin or a combination thereof in an amount such that 40 percent of the cyanate groups present in component (A) are contributed by said hydrocarbon polyaromatic cyanate resin. 3. An encapsulating composition of Claim 2 which comprises in addition to components (A) and. (B), a filler material (C) wherein (i) component (A) is the product resulting from cyanating (1) a hydrocarbon novolac resin, (2) a halogenated hydrocarbon novolac resin, (3) a combination of (1) and (2) or (4) a combination of (1), (2) or (3) and a phenol-aldehyde cyanate resin, a bisphenol A cyanate resin, a halogenated phenol-aldehyde cyanate resin, a halogenated bisphenol A cyanate resin or a combination thereof; (ii) component (B) is a cobalt salt; (iii) component (C) is present in an amount of from 50 to 80 percent by weight of the combined weight of components (A), (B) and (C); and (iv) said hydrocarbon polyaromatic cyanate resin or halogenated hydrocarbon poly¬ aromatic cyanate resin is present in an amount such that from 90 to 100 percent of the cyanate groups present in com¬ ponent (A) are contributed by said hydrocarbon polyaromatic cyanate or halogenated hydrocarbon polyaromatic cyanate resins or a combination of such resins. 4. An encapsulating composition of Claim 3 wherein (i) component (A) contains the product resulting from cyanating the product resulting from reacting phenol, cresol or a combination thereof with an unsat¬ urated hydrocarbon containing an average of from 6 to 55 carbon atoms per mole¬ cule or halogenated derivatives of such reaction products, or mixture of such hydrocarbons or halogenated derivatives thereof; (ii) ' component (B) is cobalt naphthenate, cobalt acetylacetonate or cobalt octo¬ ate; and (iii) component (C) is silica flour. 5. An encapsulating composition of Claim 3 wherein (i) component (A) contains (a) the product resulting from cya- nating the reaction product of - phenol, cresol or a combination thereof with a composition com¬ prising from 70 to 100 percent by weight of dicyclopentadiene, from zero to 30 percent by weight of C 9 -C 12 dimers of C 4 -C 6 dienes, from zero to 7 percent by weight of oligomers of C 4 -C 6 unsaturated hydrocarbons and the balance, if any, to provide 100 percent by weight of C 4 -C 6 alkanes, alkenes or dienes; (b) halogenated derivatives of the product of component (a); or (c) combinations of components (a) and (b); (ii) component (B) is cobalt naphthenate; and (iii) component (C) is silica flour. 6. An electrical component encapsulated with a composition of any one of Claims 1 to 5. 7. An electronic component encapsulated with a composition of any one of Claims 1 to 5.

Inventors: BOGAN GARY W, LUCAS PETER A, BOGAN, GARY, W., LUCAS, PETER, A.
Applicants: DOW CHEMICAL CO, THE DOW CHEMICAL COMPANY
Application year: 1986
Main classification: C08K3
IPC codes: C08G8, C08G61, C08G73, C08K3, C08K5, C08L65, H01B3