DE2315714A1 - MICROMINIATURIZED CIRCUIT ARRANGEMENT - Google Patents

Description

File number of the applicant: WA 972 001

Micromini ature i ssed chaRatIon arrangement

The invention relates to a microminiaturized circuit arrangement, in which a semiconductor wafer is attached to a substrate with the aid of a binding agent.

The manufacturing processes for large-scale integrated circuits have reached a level that allows more than 1000 active To form components in a semiconductor die with a size of about 6 χ 6 mm. The protection of these platelets However, environmental encapsulation still presents considerable difficulties. Using a frame provided with conductor tracks for support and encapsulation is widely used in semiconductor technology. One such an arrangement is shown in FIG. The substrate 2, an intermediate piece 9 and an end cap are used there for encapsulation 10, which together form a cavity in which the semiconductor wafer is arranged. Fig. 2 shows an enlarged Cross-section from the arrangement of FIG. 1. It is shown here how the semiconductor wafer 1 with the help of a Binder 3 is attached to the substrate 2. The circuits inside the semiconductor die 1 are over Connection contacts 4, leads 5 and conductor tracks 6 on the Substrate connected to external circuits. A eutectic gold-silicon alloy is generally used for the binder 3

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tion used. Here, the arrangement is brought to the eutectic temperature of the gold-silicon alloy, and then das'Hemiconductorplatechen pressed into this alloy will. The bond achieved in this way has high adhesive strength and good thermal conductivity. However, it is relative rigid and transfers mechanical stresses from the substrate to the semiconductor wafer.

The following table shows the temperature expansion coefficients some of the materials used in semiconductor technology. .

material Linear expansion coefficient 1 / ° C , 6 X io ~ ⁶ silicon 7th , 7 X io " ⁶ . Aluminum oxide 8th , 4 X io " ⁶ Novolak resin 14th X ΙΟ ' ⁶ copper 17th

It has hitherto been required for the semiconductor die and. to use materials with approximately the same coefficient of thermal expansion for the substrate in order to keep the mechanical stresses in the semiconductor wafer as low as possible. Such stresses result from occurring during operation of the integrated circuit temperature changes, which usually are in the range between 0 ° and 80 ⁰ C. For relatively large semiconductor wafers with an edge length of 6 mm, a temperature increase of 80 ° results in an expansion of about 3.5 10 mm. For a corresponding area of an aluminum oxide substrate to which the semiconductor wafer is applied by means of a eutectic gold-silicon alloy, on the other hand, there is an extension of about 4.0 x-10 "mm. The difference between the various dimensions is thus about 0.5 χ 10 ~ mm, which is relatively small. In this case, only relatively small mechanical stresses are transferred to the semiconductor wafer during operation. The production of aluminum substrates or other ceramic substrates is

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however, associated with very high costs. The procedural steps In making such substrates consist of sintering the unfired material, grinding and sawing cavities as well Polishing the surfaces. These processes are very complex and time-consuming. The cost of the completed arrangement are therefore about 5 times the cost of the die self.

If the properties of the material permit, a plastic substrate can be used instead of a ceramic substrate. These substrates are easy and inexpensive to manufacture. 3 shows a plastic substrate 8 with an inserted copper piece 7 which serves as a heat sink. The manufacturing cost of such an encapsulation is about 50% of the cost of the semiconductor die. The problem arises here, however, that the metals used as heat sinks have a considerably greater coefficient of thermal expansion than silicon. From the above table it is evident that copper has a coefficient of 17 χ ^10/0 C, which thus is more than twice as large as that of silicon. The copper substrate under a semiconductor wafer with an edge length of 6 mm thus experiences a temperature increase of 80 ° C.

_3
Expansion of about 8.6 χ 10 mm. The difference between the dimensions of copper and silicon is thus about 5.1 χ 10 ~ mm in the present example. This difference is thus 10 greater than that when using a substrate made of aluminum oxide. The mechanical stresses that occur in the process can be sufficient to destroy the connection between the semiconductor wafer and the substrate. In this case, the heat dissipation to the substrate is considerably reduced, as a result of which failure of the semiconductor wafer during operation becomes inevitable. The possibility of such damage increases with the size of the semiconductor wafer, since the difference in expansion increases linearly with it, as well as with the circuit density in the semiconductor wafer, since the heat generated during operation depends on this.

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The problem of securing semiconductor wafers with a relatively large expansion on a substrate with different thermal expansion coefficients has been solved so far by using a binder with the lowest possible thermal expansion coefficient. For example, a binder with low thermal expansion was formed from a resinous lacquer and a finely divided inert organic filler which has a negative coefficient of thermal expansion. The filler used was lithium aluminum silicate mixed with, for example, an aromatic polyamide. Experiments have shown that binders containing lithium aluminum silicate have a low resistance to moisture, a tendency to precipitate impurities and an instability of the dielectric constant and the dissipation factor. The changes in the physical properties of the lithium aluminum silicate-containing binder, which extend over a long period of time, can be explained by the ion mobility of the lithium ions in the lattice. Void spaces ^{v are formed} in the grid, through which water can penetrate. Measurements in the area showed a large increase in pH, indicating leaching of ionic contaminants. Such impurities from a binder for a semiconductor wafer which contains field effect transistors can cause a reversal of the surface charge of the semiconductor wafer and thus impair the electrical properties of the field effect transistors.

It is therefore the object of the present invention to provide a microminiaturized Circuit arrangement in which a semiconductor wafer is attached to a substrate with the aid of a bonding agent is to be specified, in which a reliable bond between the semiconductor wafer and the substrate is ensured, too when the two interconnected parts are made of materials with significantly different coefficients of thermal expansion exist. The bond should also be used in their chemical, electrical and mechanical properties

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stay stable. This task is performed with the circuit arrangement mentioned solved according to the invention in that the binder is an epoxy resin and a hardener made of aromatic diamines, which are mixed together in an approximately stoichiometric ratio, as well as a finely divided inorganic filler, the proportion of which is between 50 and 80 percent by weight of the binder. Preferably contain the hardening agent 55 to 75% metaphenylenediamine and 45 to 25% methylenedianiline and the binder an epoxy resin from the group consisting from the diglycidyl ether of bisphenol A or glycidyl ether of novolak resin and a filler selected from the group consisting of aluminum oxide, silica or zirconium orthosilicate.

The substrate can be made of plastic, ceramic or metal. The binder shows even with long-term stresses no change in physical or chemical properties. Due to its mechanical compliance, it can Avoid the occurrence of mechanical stress as far as possible when the interconnected parts expand differently.

Example 1; An analysis of the physical properties of the present binder was carried out. Samples of the binder were prepared as follows: 100 parts of the diglycidyl ether of bisphenol A having a viscosity of 13,000 to 15,0OO centipoise, an epoxy equivalency of 185 +5, a chloride ion content (hydrolyzable) of 0.03 and a sodium ion content of less than one a million parts were made. 22 parts of a eutectic mixture consisting of 60% metaphenylenediamine and 40% methylenedianiline and an iron ion content of less than 0.4 per million parts and a sodium ion content of also less than 0.4 per million parts were mixed with this resin mixture . After the resin and hardener had been thoroughly mixed, a finely divided aluminum oxide filler was added, making up 70 percent by weight of the total binder.

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constant after 1000 hours at 85 ^° C. and 85% more relative

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The spectographic analysis showed that the alumina had a total inorganic balance of less than 10 to 1 million parts, sodium ions of less than 3 to 1 million parts, and iron ions of less than 2 to 1 million parts. The binder was divided into a number of samples and ^{cured at 85 °} C. for one hour and at 150 ^° C. for a further hour. The binder obtained in this way showed the following properties: ^ -

a) Weight loss after 2000 hours at 150 ° C: 0.16%

b) Weight loss after 2000 hours at 125 ^° C.: 0.05%

c) Thermal expansion coefficient from 55 C to 154 C: 2.6 χ 10 " ⁵ / ° C.

d) Dielectric constant: originally 5.68. Dielectric constant after

Moisture: 6.01.

—2

e) Loss factor: originally 1.85 χ 10 "

Loss factor after 1000 hours at 85 ⁰ C and 85% relative humidity: 2.67 χ 10 ~ ² .

6 2

f) Tensile stress: 996 χ 10 ^ yn / em.

g) Rockwell hardness: 107.

h) Thermal gravimetric analysis: Stable up to 330 ⁰ C.

i) Differential thermal analysis: no reaction - up to 340 C.

It was the adhesive strength of the binder described with that of the known eutectic gold-silicon alloy with a connection between a silicon plate and a ceramic one Substrate compared,

Test 1: A first group of square silicon platelets with an edge length of 2.5 mm was applied to a substrate made of aluminum oxide with the aid of a eutectic gold-silicon alloy. A second group of such silicon wafers was attached to an alumina substrate using the present binder. A pin was attached to each die to apply tensile stress to the

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to be able to exercise a bond. The test with the present binder showed an average adhesive strength of 11.19 kg, while the mean bond strength for the eutectic gold-silicon alloy was 8.11 kg. The adhesive strength at the The binder described in the present example is thus larger than that of the known eutectic gold-silicon alloy.

Test 2; The ability of the binder to largely prevent the development of mechanical stresses in the event of different expansions of the semiconductor wafer and the substrate as a result of temperature changes was investigated in the following experiment. A first group of square silicon platelets with an edge length of 3.8 mm was applied to a substrate made of Novov lak resin with a linear temperature expansion coefficient of 14.4 10 ~ / ⁰ C with the aid of the present binder. A second group of silicon wafers of the same size was attached to a copper substrate with the same binder. Finally, a third group of square silicon wafers with an edge length of 7.0 mm was applied to substrates made of novolak resin, copper and aluminum using the present binder. All samples were placed in a heating chamber, the temperature of which was cycled 3 times for one hour. During one cycle, the temperature was set to -40 ° C. and +150 ° C. for 10 minutes each time. The transition between these two temperature values took place within 2 seconds. The first group of wafers on the novolak resin substrate passed 9,200 cycles without cracking or peeling. The full adhesive strength was thus retained during the entire test. The second group of die on the copper substrate was subjected to 4,200 cycles without cracking or peeling. Here too, the adhesive strength remained undiminished. The third group with the larger wafers were exposed to 1,300 cycles. No cracks or peeling were found for the three different substrates. Here, too, a Venninde

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does not affect the adhesive strength.

In the case of the known binders, which are subject to the same temperature loads were exposed, errors occurred on average after less than 500 hours. There are various possible errors. For example, a break can occur within the binder, between the binder and the semiconductor die or the Substrate or occur within the semiconductor die, whereby there may be interruptions within the conductor tracks on the semiconductor wafer. The ability of the example 1 described binder, the considerable temperature fluctuations to withstand without damage is believed to be due to its mechanical compliance. This attribute surprisingly, as it is well known that when a filler such as high purity alumina is added to an epoxy, the modulus of elasticity is increased (see e.g. Lee and Neville: Handbook of Epoxy Resins, pp. 13 and 14). A higher one Modulus of elasticity means that the material becomes more rigid and is therefore less able to move between different materials occurring differences in the expansion with temperature changes to absorb. In the case of a rigid medium, temperature cycles occur after a large number of passed through Cracks and cracks leading to the destruction of the semiconductor components to lead. The binder used in test 2 showed more than 20 times greater reliability with temperature fluctuations than the previously known binders. There is a theory for the increased resistance to the occurrence of cracks in the fact that a flow process takes place in the material when stressed, the different expansions without the Compensates for the formation of high mechanical stresses. This property makes the binder explained in Example 1 extremely high advantageous when attaching silicon wafers to the to use a wide variety of substrates. This property of the binder was not foreseeable.

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The selection of the constituents of the binder ensures that there is no contamination of the other parts of the circuitry does not occur. Such impurities can impair the function of the built-in by attacking the metallization Affect circuits and cause physical instabilities in the semiconductor device. The well-known organic Materials that are used in the encapsulation of integrated circuits can withstand prolonged exposure Ionic impurities escape, for example sodium, silicon and hydroIisable chlorides, which the Reduce the reliability of the encapsulation. The ability of the present binder to also take such impurities To withstand prolonged stresses is shown in the following test 3.

Test 3; An elevated temperature and elevated humidity test was conducted on semiconductor dies containing 44 pads which were connected to a lead frame by a flow of solder in a known manner. The aim of the attempt was to cause corrosion and destruction of the electrical connections by immersion in the binder. 25 semiconductor wafers attached to their lead frames were encapsulated with the binder according to Example 1. All electrical contacts were examined prior to the experiment. A faulty contact was always assumed if there was either an interruption in the electrical circuit or an increase in resistance of 200 milliohms at the relevant connection. The circuit arrangements were then placed in a climatic chamber in which they were exposed to a temperature of 85 ° C. and a relative humidity of 85%. A reverse bias of 40 V was applied between the contacts and the semiconductor substrate. After 2000 hours, the arrangements were removed from the climatic chamber and examined, it being shown that all connections were in perfect condition and that none of the 1100 connections that were checked showed a noticeable increase in resistance. the

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metallurgical examination of the contacts revealed that no significant Reaction between the terminal metallization or the solder and the binder had taken place. This experiment showed that the binder described was excellent Has long-term stability of its electrical and chemical properties.

The binder described in Example 1 allows certain deviations in its composition without changing its advantageous properties, ie the mechanical flexibility, the high adhesive strength, the good thermal conductivity and the stability of the electrical and chemical properties. The relative proportions of metaphenylenediamine can be varied between 55 and 75% and the relative proportions of methylenedianiline between 45 and 25%. Excessive crystallization of the hardener and brittleness of the resulting cured resin system occur outside of this compositional range. The relative proportion of the hardening agent consisting of aromatic diamines can be changed between 20 and 24 parts to 100 parts of the diglycidyl ether of bisphenol A. Either aluminum oxide, silica or zinc orthosilicate can be selected as filler, the particle size should be in the range between 6 and 12 μm . The proportion of the inorganic filler can be in the range between 50 and 80 percent by weight of the total binder.

When using epoxy resin systems for encapsulation of integrated semiconductor circuits, the use of anhydrides as hardening agents should be avoided as they cause the Have a tendency to form acidic groups at elevated temperature and humidity. These groups respond with the metallic parts of the encapsulation and thereby cause electrical short circuits. Hardening agents containing aromatic diamines have proven to be more suitable for the encapsulation of integrated circuits, as they provide a better solution

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resistance, better temperature stability and the ability to to harden faster, own. Another advantage is the absence of residual acidic groups after the hardening process and thus the formation of stable hardened materials. However, it has been found that only the diglyeidyl ether of bisphenol A and the glycidyl ether of novolak resin in cooperate in a desired manner with the hardening agent consisting of aromatic diamines.

Example 2: In this example, the composition of a further mechanically compliant binder is given. For every 100 parts of the glycidyl ether of novolak resin with an epoxy equivalent between 175 and 180, between 24 and 25 parts of the eutectic * mixture of metaphenylenediamine and methylenedianiline are added. After thoroughly mixing this resin system, 70 percent by weight of a finely divided aluminum oxide filler is added. It then cures for one hour at 85 ° C and another hour at 150 ° C. A binder is obtained whose mechanical flexibility is the same as that of the binder described in Example 1. This binding agent is therefore also suitable for fastening silicon wafers to substrates, the coefficient of thermal expansion of which can differ considerably from that of silicon.

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Claims (6)

PA ^- TEN TAN-S P RÜ C HE ί 1.) Microminiaturized circuit arrangement in which a ^ ~ ^^ semiconductor wafer is attached to a substrate with the help of a binding agent? characterized in that the binder contains an epoxy resin and a hardening agent made from aromatic diamines, which are mixed together in an approximately stoichiometric ratio, and a finely divided inorganic filler, the proportion of which is between 50 and 80 percent by weight of the binder. 2. Circuit arrangement according to claim. 1, characterized in that that the hardener contains 55 to 75% metaphenylenediamine and 45 to 25% methylenedianiline. 3. Circuit arrangement according to claim 1 or 2 _S, characterized in that the binder contains an epoxy resin from the group consisting of the diglycidyl ether of bisphenol A or glycidyl ether of Hovolakars. 4. Circuit arrangement according to one of claims 1 to 3, - characterized in that the binding agent contains a filler from the group consisting of aluminum osmium " silica or zirconium orthosilicate" 5. Circuit arrangement according to buckets of claims I to 4 _a, characterized in that the binder 20 to 24 parts of a © mtektlsoSiea mixture of Metaphenylenöiamin " and Methylentdianilia to 100 parts" diglycidyl ether of bisphenol A as well as © einea inorganic filler
Äluminiumoxydi silica or Sirkonimmorthosilikat "with 50 to 80 ■ Gewichtsproa ent äes binder contains «972 001 3098S1 / 01S 6. Circuit arrangement according to one of claims 1 to 4, characterized in that the binder 24 to 25 parts of a eutectic mixture of metaphenylenediamine and methylenedianilxn to 100 parts of glycidyl ether
Novolak resin with an epoxy equivalent of 175 bis and an inorganic filler with 50 to 80 percent by weight of the binder. ^{WA 972} ° ⁰¹ 309851/0760 Le e rs.e i te