Abstract:
A flame retardant epoxy molding compound comprises an epoxy, a hardener preferably of the novolac or anhydride type, a catalyst, a mold release agent, preferably a filler, preferably a colorant, preferably a coupling agent, an organic compound containing a higher percent of halogen (which can be part of the resin or the hardener), preferably the meta-brominated cresol epoxy novolac type, preferably containing at least about 0.5% of bromine by weight of the molding compound, a lower percent of sodium, preferably in the range of 0.03-0.06% by weight of the antimony peroxide, a lower percent of antimony pentoxide, preferably in the range of from less than about 0.8% by weight of the molding compound, and an amount of magnesium aluminum carbonate hydrate less than or about 4.0% by weight of the molding compound. The flame retardant epoxy compounds when used to encapsulate the semiconductor devices have improved high temperature stability and reliability compared to similar prior art molding compounds.

Description:
This is a continuation-in-part of application Ser. No. 418,757, filed Oct. 5, 1989, now U.S. Pat. No. 5,041,25, which is in turn a continuation-in-part of application Ser. No. 07/258,547, filed Oct. 17, 1988, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     Technical Field 
     The present invention relates to an improved method of encapsulating a semiconductor device by heat curing an encapsulating compound comprising an epoxy, a hardener, a catalyst, a mold release agent, optionally a filler, optionally a colorant, optionally a coupling agent and a flame retardant system around a semiconductor device. In the improvement, the flame retardant system comprises a lower percentage of antimony pentoxide, a lower percentage of sodium and an organic compound containing a higher percentage of halogen than prior art molding compounds. 
     In the improvement, molding compounds with an organic compound containing a higher percentage of halogen along with a lower percentage of antimony pentoxide and sodium and with a basic magnesium oxide compound has unexpected superior high temperature stability and reliability. 
     The present invention also relates to improved flame retardant thermo setting epoxy molding compounds of the type comprising an epoxy, a hardener, a catalyst, a mold release agent, optionally a filler, optionally a colorant, optionally a coupling agent and a flame retardant system wherein the flame retardant system comprises a lower percentage of antimony pentoxide, a lower percentage of sodium, an organic compound containing a higher percentage of halogen than prior art molding compounds and optionally a basic magnesium oxide compound to reduce corrosion of metal conductor lines and pads of the semiconductor device. 
     The present invention also, includes an improved encapsulated semiconductor device wherein the encapsulant is as described above, with as flame-retardant system comprising a lower percentage of antimony pentoxide, and sodium, an organic compound containing a higher percentage of halogen than prior art molding compounds and optionally a basic magnesium oxide compound to reduce corrosion of metal conductor lines and pads of the semiconductor device. 
     In all three instances the halogen-containing organic compound may be a separate ingredient, but is preferably a part of either the epoxy or the hardener. The halogen containing organic compounds can also be halogen-containing compounds which become chemically incorporated into the product of the epoxy resin and the hardener upon setting or part of other ingredients such as the lubricant or the colorant. 
     The terms &#34;epoxy molding compounds&#34; as used herein means epoxy molding compound conventionally known in the art including any material containing two or more reactive oxirane groups. For example, the epoxy molding compound may have two or more epoxy groups in one molecule, including glycidyl ether type such as, phenol novolac type, cresol novolac type and the like; glycidyl-ester type; alicyclic type; heterocylic type and halogenated epoxy resins, etc. The epoxy resins may be used either singly or as a mixture of two or more resins. 
     Similarly, the term &#34;epoxy novolac molding compound&#34; as used herein includes any phenol-derived and substituted phenol derived novolac hardener conventionally used as hardener for epoxy resins. For example, phenolic novolacs, and cresolic novolacs, are most suitable. The epoxy novolac molding compounds may be used either singly or as a mixture of two or more compounds. 
     The term &#34;catalyst&#34; as used herein means a catalyst appropriate to the hardener used to promote the curing of the present composition. Such catalysts include basic and acidic catalysts such as the metal halide Lewis acids, e.g., boron trifluoride, stannic chloride, zinc chloride and the like, metal carboxylate-salts such as stannous octoate and the like; and amines, e.g., triethylamine, imidazole derivatives and the like. The catalysts are used in conventional amounts such as from about 0.1 to 5.0% by weight of the combined weight of epoxy and hardener. 
     The term &#34;mold release agents&#34; as used herein means chemical agents commonly used to assist the release of the cured epoxy molding compounds from the mold. For example, carnauba wax; montanic acid ester wax; polyethylene wax; polytetrafluoroethylene wax; glyceral monostearate; metallic stearates; paraffin waxes and the like are suitable. 
     The term &#34;fillers&#34; as used herein means one or more of the conventional fillers such as silica, calcium carbonate, calcium silicate, aluminum oxide, glass fibers, clay, and the like. The preferred filler is silica or a mixture of predominantly silica with other filler(s). The fillers usually are used in at least 50 percent by weight of the molding compound. 
     The term &#34;colorant&#34; as used herein includes colorant commonly used in epoxy molding compound, such as carbon black, pigments, dyes and the like. 
     The term &#34;coupling agent,&#34; as used herein means a coupling agent known to improve dry electrical properties of the compound. The coupling agents may be of the silane type, characterized by the formula R&#39;Si(OR) 3  ; where R&#39; represents an organo-functional group such as amino, mercapto, vinyl, epoxy or methacryloxy, and OR represents a hydrolyzable alkoxy group attached to the silicon. Preferred coupling agents are described in U.S. Pat Nos. 4,042,550 and 3,849,187, of which the descriptions are incorporated herein by reference. 
     The term &#34;halogen-containing organic compound&#34; or &#34;organic compound containing halogen&#34;, as used herein, includes organic compound in which the halogen is present from any source including halogenation of a component or its precursor (such as a monomer) or by addition of halogen-containing monomers by reactions in which the halogen is not completely removed. 
     The halogen-containing organic compound used in a flame retardant system is preferably of the reactive type and further preferably has, as halogen, chlorine or bromine. Exemplary halogenated organic compounds are those types of polyglycidyl ether of bromophenol-formaldehyde novolac, commercially sold by Nippon Kayaku under the tradename &#34;BREN™,&#34; those described in U.S. Pat. Nos. 4,042,550 and 4,282,136, of which the descriptions are incorporated herein by reference and include halogenated bisphenol A and derivatives of bisphenol A such as tetrabromobisphenol A, and glycidyl ethers of halogenated resins such as the diglycidyl ether of tetrabromobisphenol A. 
     Preferred is meta-brominated cresol epoxy novolac available from the Dow Chemical Co. under the tradename &#34;Stable Bromine Cresol Epoxy Novolac&#34; (71842.00L type or 71970.00 type, production no. R0544-41091-21-1. These are described in U.S. Pat. Nos. 4,727,119 and 4,731,423). The 71842.00L type is of the general formula: ##STR1## The 71970.00 type contains the following ingredients: 
     
         ______________________________________Diglycidylether of Dibromotetramelthylbiphenol                      0-8%Diglycidylether of Tribromotetramethylbiphenol                      8-40%Cas No. 108935-90-6Diglycidylether of Tetrabromotetramethylbiphenol                      0-2%Cas No. 72436-58-9Reaction product of cresol, formaldehyde &amp;                      60-90%epichlorohydrinCas No. 064425-89-4______________________________________ 
    
     The halogen containing organic compound may be a separate additive or may be contained in one or more of the organic components of the molding compound, especially the epoxy or the hardener, or possibly other components such as the lubricant, or the colorant or the filler (if organic). 
     Exemplary of reactive halogen-containing organic compounds which are part of the epoxy resin are metabrominated phenolics such as meta-brominated cresol epoxy novolac. 
     The term &#34;antimony pentoxide&#34; as used herein means antimony pentoxide in any available form. Preferably, antimony pentoxide used is Nyacol A1590 commercially sold by the Nyacol Division of P.Q. Corporation which has a very low sodium content of 0.03 to 0.06% by weight of the antimony pentoxide as compared to that of 3 to 4% in prior art products such as Nyacol A1588LP. 
     The term &#34;magnesium oxide compound&#34; as used herein means any magnesium oxide in any available form capable of neutralizing the acidity of the antimony pentoxide and thereby reducing the corrosion of the metal semiconductor device lines and pads, especially in regions where two different metals are in contact with each other. Preferably, the magnesium oxide compound is magnesium aluminum carbonate hydrate commercially sold by Kyowa Chemical Industry Co. under the trade name &#34;DHT-4A.&#34; 
     Description of Background Art 
     Epoxy resin compounds have often been used for encapsulation of semiconductor or device such as integrated circuits (IC), large scale integrated circuits (LSI), transistors and diodes, etc., or other electronic components. Such encapsulants generally comprise an epoxy, a hardener, a catalyst, a mold release agent, optionally a filler, optionally a colorant and sometimes a coupling agent. 
     Exemplary formulations of these ingredients are described in U.S. Pat. No. 4,710,796 to Ikeya et al., 4,282,136 to Hunt et al., U.S. Pat. No. 4,042,550 and references cited therein and in Raymond, T, Avoiding Bond Pad Failure Mechanisms in Au-Al Systems Semiconductor Int&#39;l. p. 152-158, September 1989. Recently, the electronic industries require these epoxy molding compounds be flame retardant. Additives including halogenated compounds, transition metal oxides and hydrated alumina to improve the flame retardancy, as measured for example by Underwriters Laboratory Test 94V-0 of 1/16&#34; bar have been reported. However, at high temperatures, these flame retardant additives detract from the compatibility of the encapsulated with semiconductor devices. 
     U.S. Pat. No. 4,710,796 to Ikeya et al. teaches a resin for encapsulating semiconductor device comprising an epoxy resin, curing agent, organic phosphine compound and at least one antimony oxide. 
     U.S. Pat. No. 4,042,550 teaches epoxyanhydride molding compounds with secondary fillers including antimony trioxide or antimony tetraoxide and halogenated compounds in flame retardant systems. 
     Similarly, U.S. Pat. No. 4,282,136 to Hunt et al. describes the use of synergistic flame retardants consisting of halogen-containing organic compounds and antimony pentoxide. The reference teaches that an encapsulant employing such a flame retardant system, when used to encapsulate a semiconductor device, has improved high temperature compatibility compared to similar molding compounds with antimony trioxide or antimony tetraoxide. However, the prior art epoxy molding compounds contains a high percent of sodium which is known to cause poor performance in semiconductor devices due to current leakage. See Moltzan et al., The Evolution of Epoxy Encapsulation Compounds For Integrated Circuits: A User&#39;s Perspective, Polymer for High Technology Electronics and Protronics, ACS Sym. Series No. 346, p.521, Sept. 7-12, 1986. 
     Raymond describes the necessity of IC manufacturers keeping Br in molding compounds at a low level (around 0.6-0.8%.) based on poor dry heat reliability results with a high Br compound (1.0%). 
     While the prior art flame retardant combinations provides reasonable flame retardance and satisfactory compatibility on electronic devices, a need clearly exists for flame retardant epoxy molding compounds of all types with improved compatibility, performance, cost and lower toxicity. 
     Accordingly, it is an object of the present invention to provide an improved flame retardant thermo setting epoxy molding compound. 
     It is yet another object of the present invention to provide an improved method of encapsulating a semiconductor device. 
     It is yet another object of the present invention to provide an improved encapsulated semiconductor device. 
     These and other objects of the invention, as well as a fuller understanding of the advantage thereof, can be had by reference to the following descriptions and claims. 
     SUMMARY OF THE INVENTION 
     The foregoing objects are achieved according to the present invention by an improved epoxy molding compound comprising: 
     (a) about 5-25 percent by weight of compound of an epoxy; 
     (b) about 4-20 percent by weight of compound of a phenol-derived or a substituted phenol derived resin hardener; 
     (c) an effective amount of a catalyst for the reaction between said epoxy resin and said hardener in an amount of from about 0.1 to 10% by weight of the combined weight of epoxy and hardener; 
     (d) an effective amount of a mold release agent for the release of the cured molding compound from a mold in an amount of between about 0.01 and about 2 percent by weight of composition; 
     (e) between about 50 and 85 percent by weight of composition of a filler; and 
     (f) a flame retardant system of: 
     (1) &lt;about 0.8% antimony pentoxide by weight of molding compound; 
     (2) from about 0.01-1% sodium by weight of antimony pentoxide; and 
     (3) a reactive organic compound containing at least about 0.5% of bromine by weight of molding compound which may include one or more of the other components; and 
     (4) ≦about 4.0% by weight of molding compound of a magnesium oxide compound which is most preferably magnesium aluminum carbonate hydrate. 
     Accordingly, Table 1 below summarizes the improved epoxy molding compounds. 
     
                       TABLE 1______________________________________                         PreferredDescription        Range      RangeFormulation (1):   (%)        (%)______________________________________Brominated epoxy resin              5-25       10-17bromine content of at least   1.0-1.8molding compound   about 0.5(preferred reactiveorganic compound isStable Bromide Cresolepoxy novolac)sodium (present in the              0.01-1     0.03-0.06antimony pentoxide)antimony pentoxide &lt;0.80      0.40-0.80Magnesium aluminum ≦4.0                         .02-3.20carbonate hydrateCarbon black colorant              0.05-0.5   0.1-0.5Phenol Novolac Hardener              4-20       4-12Fused Silica (SiO2) filler              50-85      60-80silanes            0.05-2.0   0.1-1.5catalysts          0.01-10.0  0.5-2.0wax lubricants     0.01-2     0.02-1.0______________________________________ 
    
     The improved epoxy molding compounds of the present invention are suitable for use in encapsulating a semiconductor device. 
     According to the present invention, the said improved epoxy molding compounds may be prepared by any conventional method. For example, the ingredients may be finely ground, dry blended and then densified on a hot differential roll mill, followed by granulation. Generally, the ingredients (or any portion of them) may be prepared as a fine powder, fed directly into a compounding device such as an extruder prepared as a premix of raw materials. If less than all of the ingredients are present in the initial form, the remainder of the ingredients can be added prior to or during densification. 
     Densification can be by mechanical compacting using a performer or a combining mill in the case of a fine powder, or by an extruder or differential roll mill in the case of the fine powders, direct feed or premix. Premixes or densified forms (such as preforms and granular forms), containing less than all of the ingredients can also be fed to the ultimate mold in the system with the remaining ingredients in a similar or different form. 
     The present invention includes flame retardant molding compounds in any physical form or even as systems of two or more components. Where two or more components are used, one should contain the epoxy, the other the hardener. Preferably, the catalyst is in the hardener component to avoid catalyzed homopolymerization of the epoxy. 
     In a preferred embodiment, in the laboratory, the dry ingredients of the formula are preground to a fine powder and then mixed in a large plastic bag. The liquid ingredients (i.e., the silane coupling agents) are added to dry ingredients and the mixture is mixed again by hand. The mixture is then treated on a large two-roll mill (one roll heated to about 90 C. and the other cooled with tap water) until a uniform sheet (about 6&#34; wide by 24&#34; long) is obtained. The sheet is allowed to cool and then ground to a fine powder. 
     In another preferred embodiment, in the pilot plant and during large scale production, the dry ingredients are mixed in a large hopper, the liquid ingredients are added in a homogeneous manner to ensure blending, and mixing continues. This mixture is then extruded (with heating) to give a continuous sheet which is cooled and grounded. The final ground powder can be used as is, or compacted (densified) in a preformer to give tablets (preforms) of desired shape and size. 
     These compounds may be molded into various articles by application of the appropriate temperature and pressure. For example, molding conditions for the encapsulated semiconductor of the present invention may range from about 300° to 400° F., (about 149° -204° C.), preferably about 350° to about 375° F., (about 177°-191° C.), at 400 to 1,500 psi, (about 28 -105 kg/cm 2 ), for a time ranging from about 30 to 120 seconds, preferably 60 to 90 seconds. 
     Any suitable molding apparatus may be employed, such as a transfer press equipped with a multi-cavity mold. 
     The ratio between the various ingredients may vary widely. In general, the epoxy will be in proportion to a novolac hardener so as to give a mole ratio of oxirane: reactive hydroxy between about 0.8 and 1.25. Similarly, the epoxy will be in proportion to an anhydride hardener so as to give a ratio of oxirane: anhydride equivalent between about 1.0 and 1.7, preferably between about 1.11 and 1.25. 
     The catalyst employed is generally applied at levels sufficient to harden the epoxy molding compound under anticipated molding conditions. Amounts between about 0.1 and 5 weight percent (by combined weight of epoxy and hardener) are sufficient. 
     The mold release agent will be employed in amounts sufficient to give good release from the mold and also to improve the dry electrical properties of the encapsulated semiconductor device. Amounts between about 0.01 and 2 percent by weight of total compound, preferably between about 0.02 and 1 percent by weight of total compound can be used. 
     The total amount of filler may range from 0 up to about 85 percent of the total compound. Preferably, the filler comprises a total of more than 50 weight percent of the total compound and more preferably between about 60 and about 85 weight percent of the total compound. Also, preferably, between about 60 and about 80 weight percent of the total compound is a silica filler. 
     Colorants, if employed, are generally in amounts sufficient to give encapsulated devices the desired color preferably black. Amounts between about 0.1-0.5% by weight of total compound can be employed. 
     Coupling agents, and in particular silane coupling agents, are provided in amounts sufficient to give the desired dry electrical properties and preferably between about 0.05 and 2 weight percent by total weight of compound, more preferably between about 0.1 and 1.5 weight percent by total weight of compound. 
     The epoxy molding compound obtained may be used to encapsulate semiconductor devices by any conventional method. For example, the preferred improved epoxy molding formulations comprising 0.4-0.8% percentage of antimony pentoxide; 0.03-0.06% sodium content (by weight of antimony pentoxide) and an organic compound containing about 1.0-1.8% . of bromine when molded on test devices have unexpected superior high temperature stability and reliability compared to prior art formulations as disclosed in U.S. Pat. No. 4,282,136 to Hunt et al. 
     The use of a lower percentage of antimony pentoxide in the present invention is preferred because antimony pentoxide is expensive and toxic. 
     Improved epoxy molding formulations comprising 0.4-0.8  percent of antimony pentoxide, 0.03-0.06 percent of sodium (by weight of antimony pentoxide) and an organic compound containing about 1.0-1.8 percent of bromine in high temperature storage life tests produce superior test results. The high temperature storage life test is routinely performed by semiconductor manufacturers to assess electrical reliability of the devices. In the high temperature storage life test, parametric shifts in voltage output levels are monitored. The temperature at which the semiconductor is stored may be varied. The voltage output levels reflect increased resistance across the ball-bonds of the devices. 
     The improved epoxy molding formulations are uniquely effective in delaying or eliminating the failure due to parameter shifts in voltage output levels of previous semiconductor devices. In the high temperature storage life test, Motorola SN 7420 devices were encapsulated in the improved epoxy molding compound. The improved epoxy molding compound shows no failure (greater than or equal to 400 mV at a constant 16 mA current) at 200° C. out to 880 hours and no failure (greater than or equal to 250 mV at a constant 16 mA current) at 200° C. out to 418 hours while comparable samples with BREN™ with or without DHT-4A shows at least 27% failure (greater than or equal to 400 mV and a constant 16 mA current) at 200° C. in 880 hours and at least 27% failure (greater than or equal to 250 mV at constant 16 mA current) at 200° C. in 418 hours. 
     Further, the improved epoxy molding compounds gave superior high temperature storage life test results than other combination containing BREN™ with or without DHT-4A when the temperature at which the semiconductors stored was varied at a constant voltage output level. In the high temperature storage life test, Advanced Micro Devices, Inc. 7400 Type TTL devices were encapsulated in the improved epoxy molding compound. At 185° C., the improved epoxy molding shows only 3% failure after 1800 hours while comparable samples with BREN™ with or without DHT-4A shows at least 98% failure after 1800 hours. At 200° C., the improved epoxy molding shows only 1% failure after 404 hours while comparable samples with BREN™ with or without DHT-4A show at least 76% failure after 404 hours. 
     Further, the improved epoxy molding compounds contain ≦0.8% antimony pentoxide. This is especially surprising in view of the prior art teaching that a higher percent antimony pentoxide (≧1%) will give formulation with better synergistic performance. One skilled in the art of molding compound systems would not be led to use about ≦0.8% antimony pentoxide because prior art teaches use of a halogen containing organic compound with ≧1% of pentoxide is expected to give reduced parametric failures. 
     In the present invention, the improved epoxy compound obtains superior results with either ≦1.0% or ≧1.0% bromine content. This result is unexpected based on the prior art teachings that high levels of antimony pentoxide are beneficial to high temperature reliability and high levels of bromine are detrimental. One skilled in the art would not be led to use about ≧1.0% bromine content with ≦0.8% antimony pentoxide because prior art teaches the use of ≧1.0% bromine content is expected to give poor dry heat reliability results. 
     The improved epoxy molding compounds gave superior results to compounds containing no basic aluminum carbonate hydrate and antimony trioxide when the voltage levels were monitored. In the high temperature storage life test performed at 175° C., Motorola SN 7420 devices were encapsulated in the epoxy molding compound. The compound containing DHT-4A showed no failure after 1342 hours at both 250 mV and 400 mV while the compound containing no DHT-4A showed at least 90% failure after 1342 hours at 250 mV and over 70% failure after 1342 hours at 400 mV. 
     The improved epoxy molding compound contains basic magnesium aluminum carbonate hydrate instead of other bismuth-containing materials (bismuth trioxide or IXE-600, a mixture of hydrated antimony pentoxide and basic nitrate, from Toagosei Chemical Industry Co., Ltd.). DHT-4A systems are superior to other bismuth-containing material systems in maintaining the electrical reliability of certain types of logic devices. 
     The present invention is not restricted to the above ingredients but may include other ingredients which do not detract from flame retardant properties of the flame retardant agent. Accordingly, other organic or inorganic materials may be added under the above conditions, including antimony trioxide and antimony tetraoxide in total amounts less than the amount of antimony pentoxide. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     The following nonlimiting examples further illustrate the present invention relating to an improved epoxy molding compound, method and encapsulated device. All parts are by weight unless indicated otherwise. 
     EXAMPLES A-D 
     Epoxy encapsulants are prepared from the modified formulation A indicated in Table 2. The four groups of formulation differ in the presence/absence of antimony trioxide or antimony pentoxide and/or brominated resin of the following type: ##STR2## or brominated resin of the following type: ##STR3## 
     
                       TABLE 2______________________________________         ExamplesDescription     A      B        C     Dmolding compound           %      %        %     %______________________________________Fused silica    73.64  73.64    73.64 73.45fillerCarbon black    0.23   0.23     0.23  0.23coloringPhenol Novolac  7.43   7.54     7.48  7.47HardenerEpoxy Cresol    12.77  2.87     2.60  2.60Novolac resinFlexibilizers   1.96   1.96     1.96  1.96Silane coupling 0.70   0.70     0.70  0.70agentcatalyst        0.17   0.17     0.17  0.17wax lubricants  0.50   0.50     0.50  0.50Brominated bis-A*           1.74   --       --    --type resinStable Bromine  --     11.53*   --    --Cresol epoxynovolac (71482.OOL type)Stable Bromine  --     --       11.86*                                 11.86*Cresol epoxy novolac(RO544-41091-21-1 type)antimony trioxide           0.86   0.86     0.86  --antimony pentoxide           --     --       --    1.06______________________________________ *Br Content = 0.85 All examples pass a UL94V0 flammability rating at 1/8&#34; bar. 
    
     EXAMPLES E-I 
     Five more samples are prepared with antimony pentoxide. The five groups of formulation differ in the presence/absence of basic magnesium aluminum carbonate hydrate and in the presence/absence of various bromine-containing organic compounds 
     
                                           TABLE 3__________________________________________________________________________         Examples         E   F     G    H    I__________________________________________________________________________Fused silica filler         75.21             73.82 75.21                        75.18                             75.18Carbon black coloring         0.19             0.19  0.19 0.19 0.19Phenol Novolac hardener         7.21             7.54  7.21 7.25 7.25Epoxy Cresol Novolac Resin         12.06             2.87  12.53                        13.23                             4.06Flexibilizers 1.00             1.96  1.00 1.00 1.00Silane coupling agent         0.70             0.70  0.70 0.70 0.70Catalyst      0.17             0.17  0.17 0.17 0.17Wax lubricants         0.35             0.35  0.35 0.35 0.35Brominated epoxy resin         2.35*             --    1.89**                        --   --(BREN ™)Stable Bromine Cresol         --  11.55***                   --   --   10.33.sup.4 *epoxy novolac(71842.OOL type)Tetrabromo bisphenol-A         --  --    --   1.18.sup.5 *Basic magnesium aluminum         0.01             --    --   --   0.02carbonate hydrateSb.sub.2 O.sub.5         0.75             0.85  0.75 0.75 0.75__________________________________________________________________________ *% Br Content = 0.84 **% Br Content = 0.68 ***% Br Content = 0.85 .sup.4 *% Br Content = 0.76 .sup.5 *% Br Content = 0.69 All examples pass a UL 94V0 flammability rating at 1/8&#34; bar. 
    
     EXAMPLE J 
     The four compounds as described in Examples A-D are subjected to a high temperature storage life test performed in dry conditions. The test results measuring parametric shifts in voltage output levels in which a failure was a voltage output level &gt;500 mV at 24 mA, are summarized in Table 3. The test was performed in Examples A-D and on commercially available competitive molding compounds S-2, S-1 and N-1. 
     
                                           TABLE 4__________________________________________________________________________HIGH TEMPERATURE STORAGE LIFE TEST (HTSL)7400 Type TTL Devices__________________________________________________________________________       HTSL/175 C           HTSL/185 C       500 596 740  884 1238                            168 238 310  382 472 640 880Molding Compound       HRS HRS HRS  HRS HRS HRS HRS HRS  HRS HRS HRS HRS__________________________________________________________________________Competitive Cmpd. S-2       0/52           0/52               0/52 0/52                        0/52                            0/52                                0/52                                    0/52 0/52                                             0/52                                                 0/52                                                     0/52Competitive Cmpd. S-1       0/43           0/43               0/43 0/43                        0/43                            0/42                                0/42                                    0/42 0/42                                             0/42                                                 N/A+                                                     --Competitive Cmpd. N-1       0/32           0/32               0/32 0/32                        0/32                            0/41                                0/41                                    0/41 0/41                                             0/41                                                 6/41                                                     25/41ExampleA           1/53           1/53               1/53 1/53                        11/53                            0/53                                0/53                                    0/53 1/53                                             4/53                                                 46/53                                                     53/53B           5/55           5/55               6/55 6/55                        7/55                            2/55                                2/55                                    7/55 8/55                                             9/55                                                 17/55                                                     47/55C           2/54           2/54               3/54 7/54                        9/54                            2/55                                5/55                                    5/55 5/55                                             5/55                                                 8/55                                                     21/55D           0/48           0/48               0/48 0/48                        0/48                            0/48                                0/48                                    0/48 0/48                                             0/48                                                 0/48                                                     0/48__________________________________________________________________________           HTSL/200 C           92 108 124 141 158 189 205 221 254 297 362 402Molding Compound           HRS              HRS HRS HRS HRS HRS HRS HRS HRS HRS HRS HRS__________________________________________________________________________Competitive Cmpd. S-2           0/52              0/52                  0/52                      0/52                          0/52                              0/52                                  0/52                                      0/52                                          0/52                                              26/52                                                  43/52                                                      44/52Competitive Cmpd. S-1           0/42              5/42                  14/42                      37/42                          41/42                              42/42                                  --  --  --  --  --  --Competitive Cmpd. N-1           0/41              0/41                  0/41                      0/41                          0/41                              1/41                                  1/41                                      4/41                                          4/41                                              4/41                                                  4/41                                                      4/41ExampleA               1/53              18/53                  40/53                      53/53                          --  --  --  --  --  --  --  --B               2/53              4/53                  4/53                      6/53                          6/53                              34/53                                  34/53                                      40/53                                          N/A*                                              --  --  --C               0/55              4/55                  4/55                      4/55                          4/55                              18/55                                  31/55                                      33/55                                          33/55                                              36/55                                                  37/55                                                      44/55D               1/46              1/46                  1/46                      1/46                          1/46                              2/46                                  2/46                                      2/46                                          2/46                                              2/46                                                  2/46                                                      18/46__________________________________________________________________________ Parametric shifts in voltage output levels (VOL) were monitored. A failure was VOL &gt; 500 mV at 24 mA. 
    
     A review of the data shows that the antimony pentoxide sample (Example D) was far superior to the antimony trioxide samples (Examples A, B and C) in prolonging high temperature storage life. Example D was also far superior to the competitive compounds S-2, S-1 and N-1. 
     EXAMPLE K 
     The five compounds as described in Examples E-I are subjected to a high temperature storage life test under dry conditions along with competitive compounds S-2 and N-2. The test results measuring parametric shifts of voltage output levels in which a failure was a voltage output level &gt;500 mV at 24 mA are summarized in Table 5. 
     
                       TABLE 5______________________________________HIGH TEMPERATURE STORAGE TEST (HTS)7400 Type TTL Device     HTS     200 C       96      120     168   404   478Molding Compound       HRS     HRS     HRS   HRS   HRS______________________________________Competitive 0/100   2/100   6/100 80/100                                   100/100Compound S-2Competitive 0/100   0/100   0/100 5/100 100/100Compound N-2ExampleE                           0/93  76/93 93/93F           0/100   0/100   0/100 73/100                                   100/100G           1/100   1/100   1/100 89/100                                   100/100H           0/100   0/100   0/100 36/100                                   100/100I           0/100   0/100   0/100 1/100 100/100______________________________________ 
    
     EXAMPLE L 
     The five compounds as described in Examples E-I are subjected to a high temperature storage test under dry conditions along with competitive compounds S-2 and N-2 following baking at 185° C. and 175° C. The results are summarized below. 
     
                                           TABLE 6__________________________________________________________________________HIGH TEMPERATURE STORAGE (HTS) DATA FROM 185° C. &amp; 175° C.BAKE__________________________________________________________________________       HTS       185 C       638 974 1310                   1500                       1600 1700 1800 1900 2000 2150 2250Molding Compound       HRS HRS HRS HRS HRS  HRS  HRS  HRS  HRS  HRS  HRS__________________________________________________________________________Competitive Cmpd. S-2       0/100           2/100               7/100                   13/100                       18/100                            23/100                                 30/100                                      48/100                                           54/100                                                58/100                                                     75/100Competitive Cmpd. N-2       0/100           0/100               3/100                   15/100                       17/100                            23/100                                 24/100                                      26/100                                           26/100                                                29/100                                                     29/100ExampleE           0/100           0/100               6/100                   44/100                       94/100                            100/100                                 --   --   --   --   --F           0/100           0/100               4/100                   23/100                       87/100                            100/100                                 --   --   --   --   --G           0/100           0/100               20/100                   54/100                       83/100                            96/100                                 100/100                                      --   --   --   --H           0/100           2/100               81/100                   91/100                       96/100                            97/100                                 98/100                                      100/100                                           --   --   --I           0/100           0/100               0/100                   0/100                       0/100                            1/100                                 3/100                                      16/100                                           25/100                                                25/100                                                     69/100__________________________________________________________________________                          HTS                          185 C   175 C                          2300                              2380                                  500 1031                                          1500                                              2000                                                  2500                                                      3000              Molding Compound                          HRS HRS HRS HRS HRS HRS HRS HRS__________________________________________________________________________              Competitive Cmpd. S-2                          87/100                              90/100                                  1/100                                      4/100                                          7/100                                              8/100                                                  8/100                                                      8/100              Competitive Cmpd. N-2                          30/100                              30/100                                  0/100                                      0/100                                          0/100                                              0/100                                                  0/100                                                      8/100              Example              E           --  --  0/100                                      0/100                                          0/100                                              0/100                                                  0/100                                                      2/100              F           --  --  1/100                                      1/100                                          1/100                                              1/100                                                  1/100                                                      1/100              G           --  --  0/100                                      0/100                                          0/100                                              0/100                                                  0/100                                                      0/100              H           --  --  0/100                                      0/100                                          1/100                                              1/100                                                  1/100                                                      1/100              I           91/100                              96/100                                  0/100                                      0/100                                          0/100                                              0/100                                                  0/100                                                      0/100__________________________________________________________________________ 
    
     A review of the test data enumerated in Table 5 and Table 6 show that only when the three ingredients (Stable Bromine cresol epoxy novolac, antimony pentoxide and basic magnesium aluminum carbonate hydrate) are used together are the best results obtained. 
     In particular, while high temperature storage tests performed at 175° C. show no substantial difference in parameteric shifts of voltage output levels, tests performed at 185° C. and 200° C. indicate that the devices molded with an epoxy molding compound having the stable bromine cresol epoxy novolac, antimony pentoxide and basic magnesium aluminum carbonate hydrate (Example I) exhibited superior storage life. Example I also proved to be far superior to competitive compounds S-2 and N-2. 
     EXAMPLE M 
     Example I underwent reliability tests wherein the devices were subjected to high temperatures (i.e. 85° C. to 125° C.) in both dry and wet environments while being continuously operated or biased. Additionally, the devices were cycled between -65° C. to +150° C. for up to 2000 cycles. No apparent device failures were noted in any of the tests. 
     It is believed that the superior performance of Example I is due both to the partial neutralization of the acidic character of antimony pentoxide and to reduced levels of halide ions by basic ion-exchange capable magnesium aluminum carbonate hydrate, thereby preventing undesireable corrosion of the device. 
     EXAMPLE N-O 
     Two more samples are prepared with brominated epoxy resin (BREN™). The two formulations differ in the presence/absence of antimony trioxide or antimony pentoxide and in the presence/absence of basic magnesium aluminum carbonate hydrate (DHT-4A). 
     
                       TABLE 8______________________________________                 Examples                 N    O                 %    %______________________________________Fused silica filler     70.69  71.02Carbon black coloring   0.20   0.20Phenol Novolac hardener 9.42   9.18Epoxy Cresol Novolac resin                   13.89  13.43Silane coupling agent   0.70   0.70Catalyst                0.35   0.35Wax lubricants          0.45   0.44Brominated epoxy resin (BREN ™)                   3.80   3.80Antimony trioxide       0.50   --Antimony pentoxide      --     0.50Magnesium aluminum      --     0.38carbonate hydrate (DHT-4A)______________________________________ 
    
     EXAMPLE P 
     The two compounds as described in Example N-O are subjected to a high temperature storage life test under dry conditions. The compounds were stored for a variable number of hours at 175° C. and the cumulative voltage output/low state level failures are recorded. 
     
                       TABLE 9______________________________________HIGH TEMPERATURE STORAGE LIFE TEST (175° C.)SN 7420 DevicesCumulative VOL FailuresVoltage Failure Limits*  250 mV         400 mVHours    N         O          N     O______________________________________0        0/39      0/37       0/39  0/3788       0/39      0/37       0/39  0/37176      0/39      0/37       0/39  0/37198      0/39      0/37       0/39  0/37352      0/39      0/37       0/39  0/37506      0/39      0/37       0/39  0/37638      15/39     0/37       1/39  0/37814      35/39     0/37       14/39 0/37968      37/39     0/37       23/39 0/371188     38/39     0/37       26/39 0/371342     38/39     0/37       30/39 0/371496     39/39     0/37       34/39 0/371650     --        0/37       36/39 0/371804     --        0/37       37/39 0/371958     --        0/37       38/39 0/372266     --        0/37       --    0/372596     --        0/37       --    0/373124     --        1/37       --    0/37______________________________________ *Increased voltage output/low state levels (VOL) are reflective of increased resistance across the ballbonds of these devices. 400 mV represents the device manufacturers maximum specification. A typical initial value is 200 mV. 
    
     A review of the data shows that the compound containing antimony pentoxide and DHT-4A yields superior results. In particular, after 638 hours VOL failures significantly increased for Example N than for Example 0 which contains the antimony pentoxide and the magnesium aluminum carbonate hydrate. 
     EXAMPLES Q-T 
     Four more samples are prepared. The four formulations all contain antimony pentoxide, but differ in the presence or absence of bromine-containing organic compounds (BREN™ or Dow Stable-Bromine 71842 Type), and in the absence/presence of basic metal oxide (bismuth trioxide or IXE-600) or magnesium oxide compound (DHT-4A). 
     
                       TABLE 10______________________________________          Examples          Q    R        S      T          %    %        %      %______________________________________Fused silica filler            71.02  71.02    71.81                                 71.81Carbon black coloring            0.20   0.20     0.20 0.20Phenol Novolac hardener            9.18   9.18     9.18 9.18Epoxy Cresol Novolac            13.43  --       --   --resinSilane coupling agent            0.70   0.70     0.70 0.70Catalyst         0.35   0.35     0.35 0.35Wax lubricants   0.44   0.44     0.44 0.44Brominated epoxy 3.80   --       --   --resin (BREN ™)*Brominated epoxy --     16.44    16.44                                 16.44resin (Dow Stable-Br 71842 type)**Antimony trioxide            --     --       --   --Antimony pentoxide            0.50   0.50     0.50 --DHT-4A           --     0.38     --   --Bismuth trioxide 0.38   --       0.38 --IXE-600          --     --       --   0.88______________________________________ *contains 1.36 Br **contains 1.22 Br 
    
     EXAMPLE U 
     The six compounds as described in examples N-O and Q-T are subjected to a high temperature storage life test the compounds were stored for a variable number of hours at 200° C. and the cumulative voltage output/low state level failures were recorded. The test results are summarized in Table 11. 
     
                                           TABLE 11__________________________________________________________________________HIGH TEMPERATURE STORAGE LIFE TEST (200° C.)SN 7420 DevicesCumulative VOL FailuresVoltage Failure Limits250 mV                      400 mVHours    O   Q   R   S   T   N   O   Q   R   S   T   N__________________________________________________________________________0   0/37   0/37       0/36           0/36               0/33                   0/32                       0/37                           0/37                               0/36                                   0/36                                       0/33                                           0/3288  0/37   0/37       0/36           8/36               30/33                   4/32                       0/37                           0/37                               0/36                                   0/36                                       0/33                                           0/32176 1/37   15/37       0/36           14/36               32/33                   8/32                       0/37                           8/37                               0/36                                   1/36                                       4/33                                           1/32264 5/37   17/37       0/36           19/36               --  13/32                       0/37                           8/37                               0/36                                   1/36                                       12/33                                           1/32418 10/37   37/37       0/36           27/36               --  22/32                       1/37                           22/37                               0/36                                   12/36                                       19/33                                           15/32572 12/37   --  2/36           31/36               --  --  3/37                           32/37                               0/36                                   29/36                                       22/33                                           26/32748 21/37   --  4/36           31/36               --  --  5/37                           36/37                               0/36                                   32/36                                       25/33                                           29/32880 35/37   --  12/36           31/36               --  --  10/37                           37/37                               0/36                                   34/36                                       29/33                                           31/321034    36/37   --  27/36           --  --  --  19/37                           --  2/36                                   35/36                                       30/33                                           32/321188    --  --  36/36           --  --  --  21/37                           --  17/36                                   36/36                                       32/33                                           --1342    --  --  --  --  --  --  27/37                           --  31/36                                   --  33/33                                           --__________________________________________________________________________ 
    
     A review of the data shows that in prolonging the high temperature storage life of SN 7420 devices, devices having brominated epoxy resin (e.g. Dow Stable Br 71842 type) antimony pentoxide and magnesium aluminum carbonate hydrate are superior over those containing bismuth-containing materials. (Example R versus Examples S and T). Further, this combination provides superior performance in the high temperature storage life test compared to formulations containing the brominated epoxy resin BREN™ (Example R versus Example O and Q). 
     The foregoing examples are intended to illustrate without limitation, the improved flame retardant epoxy molding compound, method and encapsulated device. It is understood that changes and variation can be made therein without departing from the scope of the invention as defined in the following claims.