Materials for High-Density Electronic Packaging and Interconnection (1990) / Chapter Skim
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5 SOME SPECIFIC MATERIALS
5 SOME SPECIFIC MATERIALS
Pages 71-94
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From page 71... ...
Hybrid encapsulant materials consisting of epoxies and silicones captured a large segment of the molding compound market in the mid- 1970s because they combined some of the high- temperature performance and the high purity of the si li cones witch the mechanical properties and the solvers yes istanc~ of the epoxies . Molding compounds s ince then have moored steadily toward all - epoxy systems ~ as the high- temperature novolac materials were improved and the ionic impurity levels were driven below 100 ppm.
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From page 72... ...
The plastic edge thickness became thin, and cracking began to Occur. To alleviate this problem, the low-stress molding compounds combined several ,, ~ alstr1 outlons were used to increase the filler loading to over 72 percent by weight, thereby reducing the coefficient of thermal expansion by as much as 25 percent (21 x 10-5 to 16 x 10-5 in./in.°C)
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From page 73... ...
Market Shares of the Maj or Molding Compound Suppliers Japanese firms now hold 70 percent of the world market share in epoxy molding compounds for IC packaging. Less than a decade ago, U
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From page 74... ...
This will cause package dimensions to grow significantly despite the anticipated reductions in lead spacing. This trend will continue to put pressure on the processability of epoxy molding compounds.
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From page 75... ...
Devices such as molded-in heat spreaders or added-on cooling fins could significantly affect package manufacture and assembly, however, with attendant increases in cost. Figure 5-1 recounts the improvements in thermoses molding compounds since the 1970s, and the expected needs over the next few years.
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From page 76... ...
exhibit good high-temperature properties and are compatible with epoxies. Polytetrafluoroethylene and certain highly crosslinked hydrocarbons offer a low dielectric constant as well as high-temperature performance.
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From page 77... ...
With the use of a ceramic substrate technology for interconnections, it quickly became obvious that, with increased complexity of circuitry, it was necessary to have a means of permitting one conductor path to cross another. A number of schemes were developed to do this, using complex insulated crossovers and small bridges, but the real technology for handling this problem came in two forms.
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From page 78... ...
This is accomplished by printing the metal lines on each of several sheets of the unsintered ceramic prior to fabricating the package. The metal paste is formed by mixing the metal particles with organic binders and then patterning the metal lines by forcing the paste through a screen covered by an emulsion into which the appropriate pattern had been photolithographically etched.
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From page 79... ...
In contrast to the multilayer green tape technology, this method does not easily allow for a cavity into which an active device can be sealed and protected in an hermetic environment. OTHER CERAMIC MATERIALS This section describes some other ceramic packaging materials and makes projections about those materials that could play a prominent role in the future.
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From page 80... ...
With tape processing, they can easily provide high-reliability hermetic packages for active semiconductor devices. Low-Fire Materials Low-firing ceramic materials are generally those that fire at temperatures below 1000°C, in contrast to the 1600 °C necessary for firing aluminum oxide.
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From page 81... ...
However, the thermal expansion characteristics and sintering characteristics of this material are incompatible with typical processing conditions. Consequently, glass-bonded ceramic compositions are being developed that strive to provide lower dielectric constants than those available in aluminum oxide-based materials.
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From page 82... ...
Furthermore, the dielectric constant of aluminum nitride is approximately that of aluminum oxide. As with many covalently bonded ceramic materials, aluminum nitride also has the disadvantage of being very difficult to sinter, requiring temperatures in excess of 1900°C.
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From page 83... ...
, cited earlier, reviews typical thermal conductivity and dielectric constant relationships of some important substrate materials.
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From page 84... ...
conventional epoxy boards and multichip ceramic modules single chip carriers, (b) conventional epoxy boards and multich~p ceramic modules with single chip carriers, or (c)
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From page 85... ...
The properties of these materials range widely in a number of categories: glass transition temperatures between 250 and 400°C are available; mechanical properties ranging from brittle to very tough may be achieved; thermal stability at 250 deco 400°C is possible; dielectric constants from 2.65 to 3.4 are typical; adhesion to the ceramic, polyimide, SiO2 , or metal interfaces varies widely, but generally requires an adhesion-promotion agent; the stress in a polyimide film varies widely among commerciallyavailable materials (amorphous polyimides generally have a film stress of about ~ to 7 Ksi, whereas ordered polyimides may have film stress as low as 1 Ksi) ; and planarization also varies widely between polyimides but is generally dependent on the percent of solids in the formulation.
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From page 86... ...
The dielectric constant i s about 2.7 and the loss is very low, as expected for hydrocarbons . Polymerization does not release volatiles and high glass transition temperatures, greater than 350°C, are achieved.
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From page 87... ...
polymer insulators with lower dielectric constants. It would be useful if easily processible materials with dielectric constants as low as 2 were available.
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From page 88... ...
The value of 20 W/cm°K at room temperature is an order of magnitude better than BeO and four orders of magnitude better than epoxy. Hardness, relatively low dielectric constant, and good optical properties also favor diamond films.
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From page 89... ...
are being replaced by materials that give better dimensional control, lower dielectric constant, and greater operating temperature range. Polyimide fibers can be designed with small and even negative coefficients of linear expansion, and these are beginning to find their way into electronic substrate composites.
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From page 90... ...
This is an area in which significant work is being done, both in the United States and overseas, but the work is not very visible. Improved composite materials for packaging and interconnection should be a significant focus of future work because the opportunity to design materials with desired substrate properties is worthy of further attention in the context of high-density electronics.
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From page 91... ...
Inorganic dielectrics generally have high dielectric constants, i.e., ('2 3.8. Thus, they are not likely materials of choice for interlayer dielectrics.
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From page 92... ...
Within IBM, in 1964, there was a small, but articulate, faction that argued that SLT was threatened by integrated circuits. This issue of SLT versus integrated circuits quickly became polarized and highly emotional.
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From page 93... ...
For phase 1, it was proposed to put integrated circuit chips on the SLT substrate, which would provide the benefits of integrated circuits without having to develop a whole new package. In addition, the SLT module was consistent with the level of integration on chips at that time.
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From page 94... ...
Fortunately, the NGT program had generated interest in multilayer ceramics in IBM's Boeblingen laboratory, and researchers there continued and improved on the multilayer ceramics work that had been started in IBM's domestic laboratories. The Boeblingen effort became the basis for IBM's present TOM when this technology was reintroduced to the United States in the mid-1970s.
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