Search

Cu/adhesive hybrid bonding is an attractive approach to three-dimensional (3D) integration because it provides direct Cu Cu vertical interconnects and high mechanical stability. However, Cu/adhesive hybrid bonding at below 200 °C is still challenging because of bonding temperature mismatch between Cu Cu and polymer adhesives and lacking of effective adhesive-compatible Cu surface activation methods. In this paper, we investigate and demonstrate a “Cu-first” hybrid bonding technique by using hydrogen(H)-containing formic acid (HCOOH) vapor prebonding surface treatment for the first time. In this technique, high-quality Cu Cu bonding is obtained at 180–200 °C that is close to or even lower than the temperature of subsequent adhesive curing. We experimentally investigate the effects of the H-containing HCOOH vapor treatment for Cu Cu bonding and cyclo-olefin polymer adhesive–adhesive bonding. This technique enables Cu/adhesive hybrid bonding at below 200 °C, promising smaller thermal stress, higher throughput, and lower cost comparing to the existing “adhesive-first” hybrid bonding method.

Silicon interposer (Si-IP) technology has been used in accelerated processing units such as graphic processing units in high-performance computing because it can package a system-on-chip and high bandwidth memories. However, the conventional Si-IP has difficulty developing larger packages because of the mismatch in the coefficient thermal expansions (CTE) of the Si-IP and the organic substrate. Therefore, the Si-IP has limited capacity for improving computing performance by the application which requires more chips. We developed a multilayer glass substrate (Glass-ST) that features a stacked glass core and propose to apply this Glass-ST to a computer board. The proposed structure has no CTE mismatch and can use high density wiring. Thus, the Glass-ST enables the assembly of more large chips than is possible using the conventional Si-IP. In this study, we prepared a 100X100 mm Glass-ST with a 5/5 µm line/space and 20 µmΦ vias. We mounted nine 21X21 mm chips with 40 µm pitch micro bumps. The results revealed that conformal plated through glass vias and a fine wiring pattern had been fabricated in the Glass-ST, and that the nine chips and Glass-ST were connected by micro bumps. The maximum warpage of the nine chips was 23 µm between temperatures of 30°C and 250°C. This means that the Glass-ST can mount chips with micro bumps due to the very slight resulting warpage. In addition, we performed thermomechanical simulation to investigate the stress experienced by the micro bumps. The results show that the maximum stresses of micro bumps with pitches ranging between 10 µm and 55 um are very similar to that of 40 µm pitch micro bumps with which the real sample was packaged. We believe the improvements in the computing performance are significant by the Glass-ST technology compared to that of the conventional Si-IP technology.

High-density packaging technologies such as 2.5D interposer technology have the potential to enhance computing performance because interposer technologies can improve input/output connections for multi-chip packaging. However, it is difficult to use interposer technology to manufacture large-sized packages because of coefficient of thermal expansion (CTE) mismatches between the interposer and organic package substrate. Here, we reported a novel glass package substrate that is stacked with glass cores, and we used conductive paste with interstitial vias. The glass package substrate enables eliminating the packaging process of the interposer and low CTE of glass; thus, it is cost-effective for the printed circuit board process. The glass package substrate passed the reflow test five times, an unbiased highly accelerated stress test 300 hours, and the thermal cycle test 750 cycles. The warpage of the glass package substrate was smaller than that of conventional organic packages. The CTE of glass was the same as that of silicon; therefore, the glass package substrate can eliminate CTE mismatch. Moreover, the stress resistance for bending stress test was stronger because of the structure of the glass core. We believe that glass package substrates are suitable alternatives to interposer technologies.

2.5D and 2.1D technologies aim at improving wiring density and packaging density. However, both 2.5D and 2.1D technologies present coefficient of thermal expansion (CTE) mismatch issues and an increase in the assembly process. To overcome such limitations, we developed a glass package stacked glass core which uses the conductive paste as interlayer connection vias. We fabricated and then studied a multilayer glass package substrate. The daisy chain of such multilayer glass package substrate passed through a reflow test for five times. During the reflow process, the warpage of the multilayer glass package substrate turns to be lower than that of an organic package substrate. In addition, the CTE of the multilayer glass package substrate is approximately 3 ppm/C, as in silicon. The bending strain of the multilayer glass package substrate becomes stronger as the number of layers increase and its internal stress is lower than the glass interposer. We believe that the proposed multilayer glass package substrate will guarantee high-density wiring, with high reliability and high packaging density, and that it can be optimally used in practical applications instead of 2.5D and 2.1D technology.

Cu/adhesive hybrid bonding is a promising technology to fabricate 3D integrated microsystems with ultra-fine pitch and short vertical interconnects, low electrical resistance, and high reliability. The main remaining issues of this technology include bonding temperature mismatch between Cu-Cu (350–400 °C) and adhesive (typically ≤250 °C), long thermal-compression time (low throughput), and high thermal stress. In this paper, we present a sub-200 °C Cu/adhesive hybrid bonding method. By using H-containing HCOOH vapor pre-bonding treatment, the bonding temperature is lowered to 180–200 °C and the thermal-compression time is shortened to 600 s, enabling a Cu-first hybrid bonding approach. Cu/adhesive hybrid bonding was successfully demonstrated at bonding temperature of 180 °C. The effects of prebonding treatment temperature and time on Cu-Cu bonding and cyclo-olefin polymer (COP) adhesive bonding are investigated in detail.

Bump-less Cu/adhesive hybrid bonding is a promising technology for 2.5D/3D integration. The remaining issues of this technology include high Cu–Cu bonding temperature, long thermal-compression time (low throughput), and large thermal stress. In this paper, we investigate a Cu-first hybrid bonding process in hydrogen(H)-containing formic acid (HCOOH) vapor ambient, lowering the bonding temperature to 180 °C and shortening the thermal-compression time to 600 s. We find that the H-containing HCOOH vapor pre-bonding treatment is effective for Cu surface activation and friendly to adhesives at treatment temperature of 160–200 °C. The effects of surface activation (temperature and time) on Cu–Cu bonding and cyclo-olefin polymer (COP) adhesive bonding are studied by shear tests, fracture surface observations, and interfacial observations. Cu/adhesive hybrid bonding was successfully demonstrated at a bonding temperature of 180 °C with post-bonding adhesive curing at 200 °C.

We developed a millimeter-wave (MMW) exposure system for in vivo experiments for operating frequencies ranging from 24.5 to 95 GHz. The MMWs are localized to the rabbit ocular tissue with a spot-focus lens antenna. The MMW energy absorption and consequent temperature elevation are evaluated by numerical simulation using measured antenna distribution and precisely modeled rabbit ocular data. Results suggest that corneal damage occurs at an incident power density of 300 ${\hbox{mW/cm}}^{2}$ with our exposure system at frequencies from 26.5 to 95 GHz.

In a lead-free reflow soldering process, it is important to reduce the reflow temperature for low-heat-resistance devices such as optical devices that include organic material. We focused on In-48mass%Sn solder for optical device assembly since the melting point of the solder can be dramatically reduced to 117°C. However, InSn eutectic solder is considered to have poor mechanical properties. Thus, we investigated the effect of adding Ag and Cu to InSn-eutectic solder to improve the mechanical properties. Consequently, it was found that adding Ag and Cu to In-48mass%Sn solder improves both mechanical strength and ductility of the solder and causes AgIn 2 to disperse by being partially substituted by Cu in the solder.

We have developed Cu-Cu/adhesives hybrid bonding technique by using collective cutting of Cu bumps and adhesives in order to achieve high density 3D-SIC. It is considered that progression of fine pitch interconnection leads to lower height of bonding electrodes, resulting in narrow gap between 3D-SICs. Therefore, it is difficult to fill in adhesive to such a narrow gap 3D-SICs after bonding, so we consider that hybrid bonding of pre-applied adhesives and Cu-Cu thermocompression bonding must be advantageous, in terms of void less bonding and minimizing bonding stress by adhesives and also low electricity by Cu-Cu solid diffusion bonding. In the present study, we adapted the following process; at first adhesives were spin coated on the wafer with Cu post and then pre-baked. After that, pre-applied adhesives and Cu bumps were successfully cut by single crystal diamond bite. Typical adhesives may cause bite damage with continuous cutting, but in this research, we selected low damage adhesive against continuous cutting, which is important properties to commercial uses. Then, chips with adhesives were attached to substrates and Cu oxidation layer was removed by exposing formic acid atmosphere. Finally permanent bonding was done at 225 degree C for 30 minutes. We concluded that solid diffusion between bonded Cu bumps could be achieved and no adhesive residue could be seen between bonded interfaces by TEM/EDX analysis.

The bonding technique for high density Flip Chip(F.C.) packages requires a low temperature and a low stress process to achieve high reliability of the micro joining. Sn-Bi solder has been noted as a low temperature bonding material. Electromigration behavior of Sn-57wt%Bi flip chip interconnection with Cu post bumps was investigated. The flip chip bumps used for this experiments consisted of Cu post formed with plating and Sn-57wt%Bi solder. Two types of under bump metal(UBM) of organic substrate were studied, that is, electroless Ni(6μm)/Au(0.5μm) on Cu pad and Cu pad. Electron flow to induce the electro-migration was from organic substrate side (Cu pad) to chip side (Cu post) with current density of 40000A/cm2 at 125 degree C. At both types of the UBM, Bi migrated and accumulated to the anode side (Cu post) and Sn migrated to the cathode side (substrate pad). Each interconnect resistance has increased to about 25% and 46% within 100 hours, respectively. However, after more than 3000 hours, they were stabilized. With Ni/Au UBM pad, Cu3Sn/Cu6Sn5 intermetallic compounds (IMCs) were formed at the Cu bump side. And under the Bi layer Cu6Sn5/Ni-Sn compounds were formed. But we didn’t observe the failure like cracks or voids at the Ni layer. With Cu pad, only Cu3Sn IMC at the Cu bump side and under the Bi layer Cu6Sn5/Cu3Sn compounds were formed after 4000 hours. Although the voids were observed at Cu3Sn/Cu interface, good electrical connection was obtained.

We have developed a new Cu-Cu thermocompression bonding technique by using cut Cu bumps in order to achieve high density 3D-stacked IC (3D-SIC). Currently, Sn layer is formed between Cu bumps, and then solid-liquid bonding is made by tin melting to connect Cu bumps. But using Sn layer can cause undesirable issues, such as electro-migration and Kirkendall voids formation between Cu/Sn interfaces, which could decrease bonding reliability. Therefore we believe that Cu-Cu thermocompression bonding is an essential technology especially in 3D interconnection. In the present study, cut Cu bumps were obtained by ultra-precision cutting using a single crystal diamond bite that would give a highly smooth Cu surface (Ra:7nm). A major advantage of cut Cu bumps is that they have an amorphous-like layer on the surface. In TEM observation, it was found that about 120nm thick amorphous-like layer was formed after cutting of Cu bumps. This layer has a potential to connect bumps each other at a low temperature similar to solder bonding because amorphous-like layer accelerates a recrystallization reaction of Cu crystal. Cut Cu bumps on both sides of LSI and substrate have been successfully bonded at 250 degrees C condition. From the analysis of crystal orientation by EBSD, it was found that the bonding interface had disappeared, which means solid diffusion was occurred and crystal grain grew across the interface.

This study proposes a temperature compensation method of the complex permittivities of biological tissues and organs. The method is based on the temperature dependence of the Debye model of water, which has been thoroughly investigated. This method was applied to measured data at room temperature for whole blood, kidney cortex, bile, liver, and heart muscle. It is shown that our method can compensate for the Cole-Cole model using measured data at 20 ℃, given the Cole-Cole model based on measured data at 35 ℃, with a root-mean-squared deviation of 3～11 % and 2～6 % for the real and imaginary parts of the complex permittivities, respectively, among the measured tissues.

We have developed a new method of flip-chip bonding for LSI packaging that uses ultra-precision cutting of Au bumps to create an extremely smooth Au surface (Ra

We have developed Cu-Cu/adhesives hybrid bonding technique by using collective cutting of Cu bumps and adhesives in order to achieve high density 2.5D/3D integration. It is considered that progression of high density interconnection leads to lower height of bonding electrodes, resulting in narrow gap between ICs. Therefore, it is difficult to fill in adhesive to such a narrow gap ICs after bonding. Thus, we consider that hybrid bonding of pre-applied adhesives and Cu-Cu thermocompression bonding must be advantageous, in terms of void less bonding and minimizing bonding stress by adhesives and also low electricity by Cu-Cu solid diffusion bonding. In the present study, we adapted the following process; at first adhesives were spin coated on the wafer with Cu post and then pre-baked. After that, pre-applied adhesives and Cu bumps were simultaneously cut by single crystal diamond bite. We found that both adhesives and Cu post surfaces after cutting have highly smooth surface less than 10nm, and dishing phenomena, which might be occurred in typical CMP process, could not be seen on the cut Cu post/ adhesives surfaces.

The ellipsometry method is well known as one of methods to measure a refractive index in optical region. This method is extended to a measurement for complex permittivities of materials at a millimeter-wave frequency. This method has little limitation on a sample size because of the free space method. The uncertainty on the measurement of phases in reflection doesn’t occur because this method is based on a scalar measurement. But a large uncertainty due to a free-space method was realized. Only 2nd order Fourier coefficients are obtained in an ideal case. But measured data contained higher order coefficients up to the 6th, because all reflected electromagnetic power could not be received by a horn antenna. We propose an effective method to extract Fourier coefficients only corresponding to ellipsometry parameters. Complex permittivitie of a lossy material in millimeter-wave region can be measured in high accuracy by the improved ellipsometry method.

Sn-57Bi合金にAg添加し, その延性改善効果を調べた。溶解温度が低くAg添加量の多い場合に粗大なAg3Sn初晶が形成し, Scheilシミュレーションでは0.5mass%以上のAg添加で初晶Ag3Sn形成が予測され, その温度はAg添加量とともに急激に上昇し, 1mass%Ag合金では200℃を越える。引張試験で歪み速度を増加させた場合, 破断モードの変化からσ-e関係は対数則から外れ, 破断伸びは著しく減少する。300℃鋳造合金は, 0.5mass%Agで引張強度と破断伸びは最も大きくなり, 時効の影響は少ない。180℃鋳造合金は, Ag量増加に伴い粗大な初晶Ag3Snが増加し, 徐々に破断伸びが減少する。

In this paper, a large 2.5D glass interposer is demonstrated with 50 um chip-level interconnect (FLI), 3/3 um line and space (L/S) escape routing, and six metal layers, which are targeted for JEDEC high bandwidth memory (HBM). Our routing design suggests that double sided panel processing with 3/3 um L/S can accommodate required signal lines for HBM. Then, 3/3 um L/S transmission lines on 25mm × 30mm glass interposers with 300 um core thickness can be realized by utilizing semi additive process. Finally, 10mm × 10m dies with daisy chains can be successfully bonded to 25mm × 30mm glass interposer with 6 metal lines using copper microbumps with SnAg solder caps.

Low pressure axial flow fans without stator blades or guide vanes are generally used in order to achieve light weight, low cost and a simple structure, and to conserve space when mounted for automobile cooling system. However, since flow resistances in front and back of the fan are very strong, air tends to flow diagonally at the fan outlet side. The fan does not operate as an axial flow fan. In this report, we describe work conducted on a motor fan, mainly from the standpoint that analysis and improved understanding of actual air flow conditions lead to improved design. As for the measurement of air flow at the outlet and inlet side of the fan, the five hole-pitot tubes were used. And the reverse flow area was visualized to adhere tracer particles which are in the air flow to the pressure surface of the blades. As a result, we could predict the air flow among fan blades and portion and shape of the reverse flow area. These data were useful for designing the mixed flow fan which has the structure of an axial flow fan.

In this paper, we report a method of low temperature solid diffusion bonding. To investigate bondability of solid diffusion, we examined the effect of bump metals and bump planarization methods. Cu and Au bump were used for bump metals and CMP and ultra-precision cutting were used for bump planarization methods. We found that fine crystal layer could be formed on only cut Cu and Au bumps, and especially cut Cu bumps had a thick fine crystal layer on the surface. The layer on cut Cu bump was found to be easily to recrystallize at low temperature condition of 150 degree C. Moreover, the bonding interface of cut Cu bump disappeared at 200 degree C for 30 min, which means solid diffusion across the interface was realized with the contribution of fine crystal layer. In addition, for Cu-Cu direct bonding, formic acid treatment before bonding is effective because formic acid can react at low temperature without destroying fine crystal layer. That led to achieve high bonding strength between cut Cu bumps.

In this report, we investigated electro-migration behavior of two types of low temperature bonding. One was Sn-57 Bi using conventional C4 process. The other was Au-In Transient Liquid Phase bonding (TLP). Electron flow to induce the electro-migration was from substrate side (Ni pad) to chip side (Cu post) with current density of 40000A/cm2 at 150 degree C. In the case of Sn-57 Bi conventional C4 process, Bi quickly migrated to accumulate on the anode side (Cu post) and Sn migrated to the cathode side (substrate Ni pad). And the interconnect resistance increased until about 150 hours. Although this temperature was higher than the melting point of Sn57 Bi solder, there was no electrically break failure and the resistance was stabilized at 80% increase of initial resistance for more than 2800 hours, that was 10 times longer life of the Sn3.0wt%Ag0.5wt%Cu (SAC305) solder joint. From the cross-sectional analyses of Sn-57 Bi solder joints after the test, it was found that Bi layer and intermetallic compound (IMC) behaved as the barriers of the Cu atom migration into Sn solder. In the case of Au-In TLP bonding, remarkable change was not observed in metallic structure. And resistance was stabilized at 0.5% increase of initial for more than 1300 hours. Sn57 Bi solder joining and Au-In TLP bonding are promising candidates for the bonding technique of high density Flip Chip packages and 3D packages.

The experiment exposing the millimeter-wave (MMWs) is performed to investigate the relation between the temperature elevation at the ocular tissue and MMW exposure. The temperature and velocity distributions in front part of the eye are simultaneously measured by using Micro-Encapsulated Thermo-chromic Liquid Crystal and Fluoroptic Thermometer. It is found that the flowing patterns of aqueous humor depend on the incident power density, and these patterns affect the heat transport mechanism.

Since the opportunities that people are exposed to intermediate frequency (IF) magnetic fields (MF) are increasing, the health risk assessment of IF-MF has now become important. Because there have been few studies about long-term exposure to IF-MF with high magnetic flux density, we have developed a new apparatus capable of IF-MF exposure up to 3.9 mT for in vitro study. In this study, we found out that IF-MF did not affect both cell growth and mutagenicity using the mammalian cell line CHO-K1 and its DNA repair deficient derivatives.

The acute ocular injury threshold of 76 GHz band millimeter wave (MMW) exposure was investigated using an in vivo rabbit model. Pigmented rabbits were exposed unilaterally to 200, 100, 75, 50, 10 mW/cm2 76 GHz band MMW for 6 min with a lens antenna. Corneal opacity, epithelial injury, miosis, and ocular inflammation were present up to 2–3 days after exposure at a dose of 200 mW/cm2. No ocular changes other than reversible corneal epithelial injury were seen following exposure at 100 and 75 mW/cm2. There were no ocular changes after exposure at doses of 50 or 10 mW/cm2. Six-minute exposure to 76 GHz 10 mW/cm2 did not induce any detectable ocular tissue damage.

The ellipsometry method is extended to a measurement for complex permittivities; of materials in millimeter-wave region. We propose an effective technique based on the Fourier analysis method to eliminate an uncertainty due to the free-space method. Complex permittivities can be measured with a high degree of accuracy by the improved ellipsometry method, as named Fourier Analysis Correction Ellipsometry (FACE) Method.