Hironori Asai

Influence of ceramic surface treatment on peel-off strength between aluminum nitride and epoxy-modified polyaminobismaleimide adhesive

Peel-off strength between aluminum nitride (AlN) ceramics and a polyaminobismaleimide (PABM) adhesive is investigated after surface treatments. The surface treatments of the AlN substrates were oxygen plasma exposure, K/sub 2/O/spl middot/n(B/sub 2/O/sub 3/) aqueous solution immersion and a combination of the two. Each of the three methods increases the peel-off strength compared to that in the case of no surface treatment. In the case of the combination of oxygen plasma exposure for 60 s and K/sub 2/O/spl middot/n(B/sub 2/O/sub 3/) aqueous solution immersion for 10 min, average peel-off strength was over 1.6 N/mm, whereas that in the case of no surface treatment was 0.14 N/mm. Oxygen plasma exposure and K/sub 2/O/spl middot/n(B/sub 2/O/sub 3/) aqueous solution immersion decreased the relative amounts of carbon and hydrocarbon on the surface of as-sintered AlN substrates. On the other hand, the relative amount of hydrophilic groups, such as COO, C=O, and C-O relatively increased. This chemical change is effective for increasing peel-off strength. The results of measurement of surface free energy of the AlN substrate surface indicate that these surface treatments increase surface energy of AlN substrates from about 47 to 60 mJ/m/sup 2/. When AlN substrate was immersed in K/sub 2/O/spl middot/n(B/sub 2/O/sub 3/) aqueous solution, tiny protrusions were formed on the AlN grain surfaces. The approximate height and pitch of the protrusions were about 30 nm and 60 nm, respectively, in the case of immersion for 10 min. Most AlN grains were etched, although not all. This change in shape of grains brings about resistance to peeling and contributes to enlargement of the surface area. Due to these effects, average peel-off strength of AlN substrates with both oxygen plasma exposure and K/sub 2/O/spl middot/n(B/sub 2/O/sub 3/) aqueous solution immersion was 1.1 N/mm even after 800 cycles of thermal cycling and the value is still larger than that required for the practical package application.

Design and characteristics of a newly developed cavity-up plastic and ceramic laminated thin BGA package

The key requirements for a package are high electric and thermal performance, thinness, light weight, small size or high assembly density, and low cost. Plastic packages are superior in terms of electrical performance and cost whereas highly thermally conductive ceramic packages are superior in terms of thermal performance, weight, and size. However, these conventional plastic or ceramic packages cannot simultaneously satisfy all the requirements A new cavity-up plastic and ceramic laminated package (PCLP) has been developed that not only has superior electrical and thermal characteristics simultaneously without a heat sink, but also a thin profile and small size and is cost-effective. For example, the frequency range applicable to the PCLP exceeds 500 MHz, the maximum power dissipation is 4 W under natural convection, and the thickness is less than 2 mm. The PCLP is composed of two substrates: an electrically conductive plastic substrate and thermally conductive ceramic substrate. The plastic substrate, made of liquid crystal polymer (LCP) and copper, forms a flexible printed circuit (FPC). LCP is a suitable material since it has low water absorption, low dielectric constant, and low dielectric loss. The ceramic substrate is cofired tungsten-metallized aluminum nitride (AlN). It has high thermal conductivity and its coefficient of thermal expansion (CTE) is close to that of silicon. The AlN substrate also supports mechanically both the FPC and the semiconductor chip. The package is made using simple processes: both FPC and AIN substrate are single insulation layers; interconnection technologies are simple, for example, screened bump interconnection and lamination; and a conventional pattern formation is used, for example, screen printing. The measured electrical resistance is 450 m/spl Omega/ (line length 14.7 mm, width=50 /spl mu/m), which was about 1/10 of that for a simple ceramic cofired package of the same dimensions with a tungsten conductor. The measured thermal resistance is 10.8/spl deg/C/W under natural convection without a heat sink. In this paper the PCLPs design concept, configuration and performance characteristics are reported.

Titanium nitride-molybdenum metallizing method for aluminum nitride

A paste containing molybdenum (Mo) and titanium nitride (TiN) powders was printed on aluminum nitride (AlN) substrates and postfired. The adhesion strength of metallized substrates with Ni/Au plate was about 25 kgf/2.5 mm and was unchanged after the thermal cycle test. TiN-Mo does not adhere to the grain boundary phase in AlN substrate, or to the surface oxide layer, but to the AlN grain itself. This method, therefore, seems to be applicable to any kind of AlN substrate, which may have different grain boundary oxide phases and thermal conductivities. This TiN-Mo metallized AlN substrate was tried as a replacement for a beryllium oxide (BeO) heat sink, which has been used for RF power transistors. There was no trouble in assembling the AlN heat sinks into transistors. Thermal resistance and electrical properties for transistors with AlN heat sinks were almost equal to those for transistors with BeO heat sinks. The TiN-Mo metallized AlN substrates were found to be suitable for replacing BeO substrates as the heat sinks for semiconductor devices. >

A thin and low thermal resistance aluminum nitride BGA package for high speed DSP devices

Low thermal resistance and high TCT (temperature cycle test) reliability have been attained by thin AlN BGA package structure. High speed signal transmission for multimedia DSP (digital signal processor) has been analyzed by computer simulation. The package has 0.6 mm body thickness, which is 1/3 of ordinary ceramic packages. A low thermal resistance of 4.8 /spl deg/C/W has been attained without a heat sink and with no air cooling while mounted on a PWB having 4 conductive layers. Scattering parameters were measured up to 9 GHz and applied to 250 MHz clock signal simulation. No deterioration of signal waveforms was observed during the simulation. The effects of package thickness and package size have been discussed from the thermal resistance and TCT reliability point of view. Thicker and larger package size provided lower thermal resistance. The developed package thickness and size (35/spl times/35 mm) have been determined by taking into account the application field of mobile PCs (personal computers) and through simulation. The package thickness versus TCT reliability has been discussed, and then the TCT has been carried out under an assembled condition on a PWB, and MTTF of 1 k cycles has been derived.

Synthesis and Characterization of β-SiAlON Phosphor Powder Prepared by Reduction Nitridation of a Zeolite

Rare-earth activated oxynitride or nitride luminescent materials have attracted considerable attention due to their potential applications as phosphors and pigments. Eu2+-doped -sialon has been reported to represent a new class of green phosphors with high efficiency. In this study, -sialon phosphor was synthesized by reduction nitridation of a zeolite. Eu ion-exchanged zeolite was fired at 1400 °C for 1 hour under NH3 gas containing 0.5 vol%C3H8. As a result, formation of -sialon with green emission under UV irradiation was confirmed.

30.3: Reduction of Electron‐Beam‐Induced Degradation of ZnS Green Phosphor Coated with Phosphate

Electron-beam-induced luminescence degradation is found to be reduced in ZnS: Cu, Al phosphor coated with a limited low content of phosphate. The behavior of the degradation is correlated with the quantities of SO2 and H2O gases released from the phosphors, analyzed by temperature programmed desorption-mass spectrometry (TPD-MS) and transmission electron microscopy (TEM) observations. We find that the layer coated with the appropriate phosphate content is uniform and continuous, which prevents the surface chemical reactions that cause the degradation.

Influence of the grain boundary phase on the mechanical strength at aluminum nitride substrate surfaces

The influence of grain boundary phases on the mechanical strength at aluminum nitride (AlN) substrate surfaces, after a wet chemical process, was studied using AlN substrates doped with 2 wt% CaO or 4 wt% Y/sub 2/O/sub 3/. Mechanical strength was measured by pin pull-off, pin bending tests and Vickers hardness measurements. Test specimens were obtained by the processes of lapping, polishing, thin-film metallizing, photoengraving, plating, and brazing. The test results showed that the mechanical strength at the surface of Y/sub 2/O/sub 3/-AlN substrates was higher than at CaO-AlN surfaces, where it was under the adhesion strength between the metallization layer and the AlN substrate. The mechanical strength at the surface of the CaO-AlN substrate was lost during patterning and plating. This was accompanied by an important weight loss in HNO/sub 3/ and K/sub 2/O/spl middot/n(B/sub 2/O/sub 3/) aqueous solution, due to dissolution of the grain boundary phase. The reason for the difference in the mechanical surface strength of AlN substrates after patterning and plating is that the CaO-AlN grain boundary phase dissolves in the chemical solution in the process more easily than the Y/sub 2/O/sub 3/-AlN gram boundary phase. The Y/sub 2/O/sub 3/-AlN substrate showed unchanged pin pull-off and bending strength even after thermal cycling (1000 cycles) and 1000 h of a pressure cooker test. Although the CaO-AlN grain boundary phase seemed to cover all the grains, thermal conductivity was only slightly affected, because the grain boundary film was very thin.

An organic and ceramic laminated BGA package with high thermal and electrical performance characteristics

A new structural face-up LSI package has been developed. The package shows low thermal resistance without a heatsink and low inductance, capacitance, and resistance values. The package is thin enough for portable multimedia equipment applications, with a thickness of 0.5 mn (not including ball height). The measured thermal resistance was 11/spl deg/C/W under natural convection without a heatsink. The simulated inductance and capacitance were 6.7 nH and 1.1 pF respectively, and measured resistance was 520 m/spl Omega/ (line length=14.7 mm, width=60 /spl mu/m). The package consists of a resin film and a ceramic substrate. The film is a liquid crystal polymer (LCP) and the substrate is aluminum nitride (AlN). LCP is a suitable material for buried-bump interconnection technology (B2it/sup TM/). AlN has high thermal conductivity and its coefficient of thermal expansion (CTE) is close to that of silicon. Both materials were laminated by an adhesive agent. This material combination provides a thin structure, low thermal resistance, and low LCR which are suitable for portable multimedia electrical equipment. This paper reports the configuration and performance characteristics of this newly developed package.

Titanium nitride-molybdenum metallizing method for aluminium nitride

A paste containing molybdenum (Mo) and titanium nitride (TiN) powders was printed on aluminium nitride (AlN) substrates and fired. The adhesive strength of substrates metallized with Ni/Au plate was about 25 kg/2.5 mm/sup 2/ and was unchanged after a thermal cycle test. TiN-Mo does not adhere to the grain boundary phase of the AlN substrate nor to the surface oxide layer but to the AlN grain itself. This method, therefore, seems to be applicable to any kind of AlN substrate, which can have different grain boundary oxide phases and thermal conductivities. This TiN-Mo metallized AlN substrate replaced a beryllium oxide (BeO) heat sink, which has been used for RF power transistors. There was no trouble in assembling the AlN heat sinks into transistors. Thermal resistance and electrical properties of transistors with AlN heat sinks were almost equal to those of transistors with BeO heat sinks.<<ETX>>