Thin-film multilayer packaging substrates

Kyocera has been conducting research and development on AIN and LTCC for more than 10 years, and has produced many kinds of AlN and LTCC products, such as Cer-Quad and multilayer packages, in addition to thin film substrates. Now, we have developed three materials for packages. The first is a novel AlN material (AN75W) that can co-fired at low temperature to reduce cost. The second is a novel LTCC that has a high thermal coefficient of expansion close to that for FR-4. The third is also a novel LTCC that has low permittivity... 

The melting point can also be determined in a penetration-mode measurement, which is important in the characterization of multilayer polymer hlms and coatings. Multilayer thin films are used primarily as packaging materials in order to control the end-use properties, such as selective atmosphere permeability or toughness. TMA in the penetration mode can characterize multilayer films in terms of layer thickness as shown in Fig. 4.11. Here, a multilayer film coated on a foil substrate was characterized in a penetration-mode experiment. Two distinct changes due to the penetration of the probe are clear at 103 °C and 258 °C, suggesting that two layers of film were coated onto the metal substrate.The thicknesses of the layers were measured as 93 pm (polymer 1) and 15 pm (polymer 2). These temperatures are close to the melting points... 

Aluminum nitride has been demonstrated to be suitable for blank substrates for high power and high frequency applications. Substrates from many sources are available for thick or thin film metaUization. Thick film paste manufacturers now supply pastes formulated for aluminum nitride. The multilayer process described in the previous section has also been adapted for aluminum nitride. Both multilayer substrates and packages are available commercially. 

Ordered polymer films made from poly benzthiazole (PBZT) and poly benzoxazole (PBO) can be used as substrates for multilayer printed circuit boards and advanced interconnects to fill the current need for high speed, high density packaging. Foster-Miller, Inc. has made thin substrates (0.002 in.) using biaxially oriented liquid crystal polymer films processed from nematic solutions. PBZT films were processed and laminated to make a substrate with dielectric constant of 2.8 at 1 MHz, and a controllable CTE of 3 to 7 ppm/°C. The films were evaluated for use in multilayer boards (MLBs) which require thin interconnect substrates with uniform controllable coefficient of thermal expansion (CTE), excellent dielectric properties, low moisture absorption, high temperature capability, and simple reliable processing methods. We found that ordered polymer films surpass the limitations of fiber reinforced resins and meet the requirements of future chip-to-chip interconnection. 

TLCPs have many outstanding properties that uniquely qualify them for these high performance multilayer boards (12). Table 7 compares the applicability of LCPs with other state-of-the-art materials for electronic packaging. They can be made into very thin, self-supporting films (<50 J.m) with a controllable CTE. By processing LCP films as described above, circuit substrates can be manufactured with a CTE around 7 ppm/°C and thermal stability over 250°C. TLCPs do not require secondary resins for fabrication into MLBs, they can be thermally bonded to themselves and to copper foil. Control of molecular orientation has been shown to result in a substrate with the desired CTE of 6 to 7 ppm/°C for matching alumina, or 16 ppm/°C for matching copper. 

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