Silver-glass die attach and large-area dice

Sintered nanoscale silver joint is an emerging lead-free die-attach solution for high-temperature packaging because of silver's high melting temperature. For bonding small chips, the nanosilver solution can be achieved with a simple heating profile under atmospheric pressure. However, for bonding large-area chips, e.g. > 1 cm2 IGBT chips, uniaxial pressure of a few MPa has been found necessary during the sintering stage of the bonding process, which is carried out at temperatures below 275°C. Hot-pressing at high temperatures can cause significant wear and tear on the processing equipment, resulting in high maintenance cost. In this study, we ran a series of experiments aimed at lowering the hot-pressing temperature. Specifically, we examined a process involving hot-press drying, followed by sintering without any applied pressure. A fractional factorial design of experiments was used to identify the importance and interaction of various processing parameters, such as hot-pressing pressure/temperature/time and sintering temperature/time, on the final bond quality of sintered nanosilver joints. Based on the results, a simpler process, consisting of hot-press drying at 180°C under 3 MPa, followed by sintering at 275°C under atmospheric pressure was found to produce attachments with die-shear strength in excess of 30 MPa.

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Low Temperature Die Attach Material

MRS Proceedings ◽

10.1557/proc-167-199 ◽

1989 ◽

Vol 167 ◽

Author(s):

Mark A. Blocker ◽

Tom L. Herrington ◽

My N. Nguyen

Keyword(s):

Heat Treatment ◽

Thermo Gravimetric Analysis ◽

Gravimetric Analysis ◽

Large Area ◽

Thermo Gravimetric ◽

Organic System ◽

Die Attach ◽

Volatile Organic ◽

Lower Temperature ◽

Sintering Characteristics

AbstractA new silver lead phosphovanadate glass die attach material is discussed. Its sintering characteristics are examined by dilatometry and the organic system by thermo gravimetric analysis. Sintering is found to occur at lower temperature than conventional silver glass systems. This is caused by reaction between silver and one of the glass components during heat treatment. The vehicle is found to evaporate faster allowing void free processing for large area dice.The new glass combined with a more volatile organic system has produced a single pass die attach material which can be fired as low as 360°C.

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Chip on Board Packaging and Thermal Solutions for a 100 W Large Monolithic LED

Journal of Microelectronics and Electronic Packaging ◽

10.4071/1551-4897-6.2.143 ◽

2009 ◽

Vol 6 (2) ◽

pp. 143-148

Author(s):

Jay G. Liu ◽

Daxi Xiong ◽

Paul Panaccione

Keyword(s):

Power Systems ◽

Thermal Resistance ◽

Input Power ◽

High Current ◽

Large Area ◽

Die Attach ◽

Total Input ◽

Thermal Solution ◽

Current Operation ◽

Heat Spreading

Thermal challenges are now widely recognized as one of the key barriers to LED's fast penetration to broader market. This paper demonstrates an effective packaging and thermal solution for a commercial realization of a large area monolithic LED of 12 mm2, with high current operation and total input power as high as 100 W. A direct chip on board (COB) die attach method was used to eliminate one level of interface such as existed in an SMD LED on an insulated metal substrate. High thermal conductivity LED submount and copper core board were designed for effective heat spreading without a dielectric in the thermal path. The thermal resistance of the 12 mm2 LED from junction to heat sink, including core board and associated TIM1 and TIM2, is as low as 0.7°C/W. A thermal model was developed using FEA to describe the temperature and thermal resistance at each interface, and is shown to be in agreement with measured data. The LED chipsets described here have been used to power systems such as rear projection TVs and front projectors.

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Silver Sintering Paste Rendering Low Porosity Joint for High Power Die Attach Application

Additional Conferences (Device Packaging HiTEC HiTEN & CICMT) ◽

10.4071/2016-hitec-134 ◽

2016 ◽

Vol 2016 (HiTEC) ◽

pp. 000134-000142 ◽

Cited By ~ 6

Author(s):

Sihai Chen ◽

Christine LaBarbera ◽

Ning-Cheng Lee

Keyword(s):

Shear Strength ◽

Thermal Aging ◽

Processing Condition ◽

Total Porosity ◽

Temperature Cycling ◽

Large Area ◽

Die Attach ◽

Aging Test ◽

Silver Sintering ◽

Sintered Ag

Abstract Silver joints with ~10% porosity for die-attach have been achieved with specially engineered Ag sintering pastes, through combined pressureless sintering process plus thermal aging. The pastes developed in this work have the following advantages: 1) they can be used under pressure-less processing condition; 2) they are compatible with conventional reflow oven, resulting in a higher through-put as compared to that of stepwise heating oven; 3) they can be used under air reflow condition; 4) a highly reliable joint has been obtained as judged from the shear strength results from thermal aging and temperature cycling tests. The silver sintering pastes are versatile in bonding different metallization surface including Au, Ag and Cu. It can also be used in bonding large area (10mm × 10mm) dies. Shear test results under varied temperatures implied that the maximum service temperature of Ag sintered joints can be as high as 470 – 530 °C, depending on the shear strength pass criteria, and this is more than 250°C higher than that of high-Pb joints. Thermal aging test at 250°C for the joints generated on Ag-die/Au-DBC combination revealed that Ag continuously consolidates in the bulk phase resulting in the formation of larger pores with reduced numbers as compared to that of untreated samples. At the same time, it diffuses to sintered Ag/Au-DBC interface to form a dense Ag layer induced by alloying with Ni(Au) and Cu, which strengthened the bonding. A large bondline thickness is critical for obtaining highly reliable joints. The total porosity of the joint is found slightly decreased during the course of 3200h aging test. Temperature cycling at −55 °C to 200°C shows that the silver joints are stable for at least 1000 cycles.

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Convergent Beam Electron Diffraction

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100070072 ◽

1978 ◽

Vol 36 (3) ◽

pp. 304-315

Author(s):

G. Lehmpfuhl

Keyword(s):

Electron Diffraction ◽

Diffraction Pattern ◽

Crystal Surface ◽

Diffraction Spot ◽

Crystal Thickness ◽

Large Area ◽

Electron Microscopic ◽

Additional Information ◽

Microscopic Investigations

Introduction In electron microscopic investigations of crystalline specimens the direct observation of the electron diffraction pattern gives additional information about the specimen. The quality of this information depends on the quality of the crystals or the crystal area contributing to the diffraction pattern. By selected area diffraction in a conventional electron microscope, specimen areas as small as 1 µ in diameter can be investigated. It is well known that crystal areas of that size which must be thin enough (in the order of 1000 Å) for electron microscopic investigations are normally somewhat distorted by bending, or they are not homogeneous. Furthermore, the crystal surface is not well defined over such a large area. These are facts which cause reduction of information in the diffraction pattern. The intensity of a diffraction spot, for example, depends on the crystal thickness. If the thickness is not uniform over the investigated area, one observes an averaged intensity, so that the intensity distribution in the diffraction pattern cannot be used for an analysis unless additional information is available.

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TEM Study of a Tilt Boundary in Hot-Pressed Silicon

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100097454 ◽

1981 ◽

Vol 39 ◽

pp. 160-161

Author(s):

C. B. Carter ◽

J. Rose ◽

D. G. Ast

Keyword(s):

Electron Diffraction ◽

Imaging Technique ◽

Interface Structure ◽

Large Area ◽

Weak Beam ◽

Lattice Fringe ◽

Electron Diffraction Technique ◽

Tilt Boundaries ◽

Beam Technique ◽

Twist Boundaries

The hot-pressing technique which has been successfully used to manufacture twist boundaries in silicon has now been used to form tilt boundaries in this material. In the present study, weak-beam imaging, lattice-fringe imaging and electron diffraction techniques have been combined to identify different features of the interface structure. The weak-beam technique gives an overall picture of the geometry of the boundary and in particular allows steps in the plane of the boundary which are normal to the dislocation lines to be identified. It also allows pockets of amorphous SiO2 remaining in the interface to be recognized. The lattice-fringe imaging technique allows the boundary plane parallel to the dislocation to be identified. Finally the electron diffraction technique allows the periodic structure of the boundary to be evaluated over a large area - this is particularly valuable when the dislocations are closely spaced - and can also provide information on the structural width of the interface.

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P20 phosphor on polyimide as a large area high-resolution transmission screen for slow scan CCD systems

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100136477 ◽

1995 ◽

Vol 53 ◽

pp. 20-21

Author(s):

C. C. Ahn ◽

S. Karnes ◽

M. Lvovsky ◽

C. M. Garland ◽

H. A. Atwater ◽

...

Keyword(s):

Mechanical Stability ◽

High Energy ◽

Practical Implementation ◽

Line Pair ◽

Modulation Transfer ◽

Large Area ◽

Ccd Imaging ◽

Transmission Electron ◽

The One ◽

Beam Broadening

The bane of CCD imaging systems for transmission electron microscopy at intermediate and high voltages has been their relatively poor modulation transfer function (MTF), or line pair resolution. The problem originates primarily with the phosphor screen. On the one hand, screens should be thick so that as many incident electrons as possible are converted to photons, yielding a high detective quantum efficiency(DQE). The MTF diminishes as a function of scintillator thickness however, and to some extent as a function of fluorescence within the scintillator substrates. Fan has noted that the use of a thin layer of phosphor beneath a self supporting 2μ, thick Al substrate might provide the most appropriate compromise for high DQE and MTF in transmission electron microcscopes which operate at higher voltages. Monte Carlo simulations of high energy electron trajectories reveal that only little beam broadening occurs within this thickness of Al film. Consequently, the MTF is limited predominantly by broadening within the thin phosphor underlayer. There are difficulties however, in the practical implementation of this design, associated mostly with the mechanical stability of the Al support film.

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Study of Tip-Surface Interactions in Scanning Tunneling Microscopy (STM) by Reflection Electron Microscopy (REM)

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100180355 ◽

1990 ◽

Vol 48 (1) ◽

pp. 320-321

Author(s):

W. Lo ◽

J.C.H. Spence ◽

M. Kuwabara

Keyword(s):

High Resolution ◽

Elastic Strain ◽

Tunneling Current ◽

Surface Damage ◽

Surface Interactions ◽

Graphite Surface ◽

Scanning Tunneling ◽

Large Area ◽

Tunneling Microscopy ◽

High Resolution Tem

Work on the integration of STM with REM has demonstrated the usefulness of this combination. The STM has been designed to replace the side entry holder of a commercial Philips 400T TEM. It allows simultaneous REM imaging of the tip/sample region of the STM (see fig. 1). The REM technique offers nigh sensitivity to strain (<10−4) through diffraction contrast and high resolution (<lnm) along the unforeshortened direction. It is an ideal technique to use for studying tip/surface interactions in STM.The elastic strain associated with tunnelling was first imaged on cleaved, highly doped (S doped, 5 × 1018cm-3) InP(110). The tip and surface damage observed provided strong evidence that the strain was caused by tip/surface contact, most likely through an insulating adsorbate layer. This is consistent with the picture that tunnelling in air, liquid or ordinary vacuum (such as in a TEM) occurs through a layer of contamination. The tip, under servo control, must compress the insulating contamination layer in order to get close enough to the sample to tunnel. The contaminant thereby transmits the stress to the sample. Elastic strain while tunnelling from graphite has been detected by others, but never directly imaged before. Recent results using the STM/REM combination has yielded the first direct evidence of strain while tunnelling from graphite. Figure 2 shows a graphite surface elastically strained by the STM tip while tunnelling (It=3nA, Vtip=−20mV). Video images of other graphite surfaces show a reversible strain feature following the tip as it is scanned. The elastic strain field is sometimes seen to extend hundreds of nanometers from the tip. Also commonly observed while tunnelling from graphite is an increase in the RHEED intensity of the scanned region (see fig.3). Debris is seen on the tip and along the left edges of the brightened scan region of figure 4, suggesting that tip abrasion of the surface has occurred. High resolution TEM images of other tips show what appear to be attached graphite flakes. The removal of contamination, possibly along with the top few layers of graphite, seems a likely explanation for the observed increase in RHEED reflectivity. These results are not inconsistent with the “sliding planes” model of tunnelling on graphite“. Here, it was proposed that the force due to the tunnelling probe acts over a large area, causing shear of the graphite planes when the tip is scanned. The tunneling current is then modulated as the planes of graphite slide in and out of registry. The possiblity of true vacuum tunnelling from the cleaned graphite surface has not been ruled out. STM work function measurements are needed to test this.

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