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Article
Publication date: 8 February 2008

Rabindra N. Das, Frank D. Egitto and Voya R. Markovich

The purpose of this paper is to discuss the use of epoxy‐based conducting adhesives in z‐axis interconnections.

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Abstract

Purpose

The purpose of this paper is to discuss the use of epoxy‐based conducting adhesives in z‐axis interconnections.

Design/methodology/approach

A variety of conductive adhesives with particle sizes ranging from 80 nm to 15 μm were laminated into printed wiring board substrates. SEM and optical microscopy were used to investigate the micro‐structures, conducting mechanism and path. The mechanical strength of the various adhesives was characterized by 90° peel test and measurement of tensile strength. Reliability of the adhesives was ascertained by IR‐reflow, thermal cycling, pressure cooker test (PCT), and solder shock. Change in tensile strength of adhesives was within 10 percent after 1,000 cycles of deep thermal cycling (DTC) between −55 and 125°C.

Findings

The volume resistivity of copper, silver and low‐melting point (LMP) alloy based paste were 5 × 10−4, 5 × 10−5 and 2 × 10−5 Ω cm, respectively. Volume resistivity decreased with increasing curing temperature. Adhesives exhibited peel strength with Gould's JTC‐treated Cu as high as 2.75 lbs/in. for silver, and as low as 1.00 lb/in. for LMP alloy. Similarly, tensile strength for silver, copper and LMP alloy were 3,370, 2,056 and 600 ψ, respectively. There was no delamination for silver, copper and LMP alloy samples after 3X IR‐reflow, PCT, and solder shock. Among all, silver‐based adhesives showed the lowest volume resistivity and highest mechanical strength. It was found that with increasing curing temperature, the volume resistivity of the silver‐filled paste decreased due to sintering of metal particles.

Research limitations/applications

As a case study, an example of silver‐filled conductive adhesives as a z‐axis interconnect construction for a flip‐chip plastic ball grid array package with a 150 μm die pad pitch is given.

Originality/value

A high‐performance Z‐interconnect package can be provided which meets or exceeds JEDEC level requirements if specific materials, design, and manufacturing process requirements are met, resulting in an excellent package that can be used in single and multi‐chip applications. The processes and materials used to achieve smaller feature dimensions, satisfy stringent registration requirements, and achieve robust electrical interconnections are discussed.

Details

Circuit World, vol. 34 no. 1
Type: Research Article
ISSN: 0305-6120

Keywords

Article
Publication date: 18 May 2010

Rabindra N. Das, Frank D. Egitto and Voya R. Markovich

Material formulation, structuring and modification are key to increasing the unit volume complexity and density of next generation electronic packaging products. Laser processing…

Abstract

Purpose

Material formulation, structuring and modification are key to increasing the unit volume complexity and density of next generation electronic packaging products. Laser processing is finding an increasing number of applications in the fabrication of these advanced microelectronic devices. The purpose of this paper is to discuss the development of new laser‐processing capabilities involving the synthesis and optimization of materials for tunable device applications.

Design/methodology/approach

The paper focuses on the application of laser processing to two specific material areas, namely thin films and nanocomposite films. The examples include BaTiO3‐based thin films and BaTiO3 polymer‐based nanocomposites.

Findings

A variety of new regular and random 3D surface patterns are highlighted. A frequency‐tripled Nd:YAG laser operating at a wavelength of 355 nm is used for the micromachining study. The micromachining is used to make various patterned surface morphologies. Depending on the laser fluence used, one can form a “wavy,” random 3D structure, or an array of regular 3D patterns. Furthermore, the laser was used to generate free‐standing nano and micro particles from thin film surfaces. In the case of BaTiO3 polymer‐based nanocomposites, micromachining is used to generate arrays of variable‐thickness capacitors. The resultant thickness of the capacitors depends on the number of laser pulses applied. Micromachining is also used to make long, deep, multiple channels in capacitance layers. When these channels are filled with metal, the spacings between two metallized channels acted as individual vertical capacitors, and parallel connection eventually produce vertical multilayer capacitors. For a given volume of capacitor material, theoretical capacitance calculations are made for variable channel widths and spacings. For comparison, calculations are also made for a “normal” capacitor, that is, a horizontal capacitor having a single pair of electrodes.

Research limitations/implications

This technique can be used to prepare capacitors of various thicknesses from the same capacitance layer, and ultimately can produce variable capacitance density, or a library of capacitors. The process is also capable of making vertical 3D multilayer embedded capacitors from a single capacitance layer. The capacitance benefit of the vertical multilayer capacitors is more pronounced for thicker capacitance layers. The application of a laser processing approach can greatly enhance the utility and optimization of new materials and the devices formed from them.

Originality/value

Laser micromaching technology is developed to fabricate several new structures. It is possible to synthesize nano and micro particles from thin film surfaces. Laser micromachining can produce a variety of random, as well as regular, 3D patterns. As the demand grows for complex multifunctional embedded components for advanced organic packaging, laser micromachining will continue to provide unique opportunities.

Details

Circuit World, vol. 36 no. 2
Type: Research Article
ISSN: 0305-6120

Keywords

Article
Publication date: 20 November 2009

Rabindra N. Das, Steven G. Rosser, Konstantinos I. Papathomas, Tim Antesberger and Voya R. Markovich

Embedded passives account for a very large part of today's electronic assemblies. This is particularly true for products such as cellular phones, camcorders, computers, and…

Abstract

Purpose

Embedded passives account for a very large part of today's electronic assemblies. This is particularly true for products such as cellular phones, camcorders, computers, and several critical defence devices. Market pressures for new products with more features, smaller size and lower cost demand smaller, compacter, simpler substrates. An obvious strategy is to reduce the number of surface mounted passives by embedding them in the substrate. In addition, current interconnect technology to accommodate surface mounted passives imposes certain limits on board design which constrain the overall system speed. Embedding passives is one way to minimize the functional footprint while at the same time improving performance. The purpose of this paper is to describe the development of a thin film technology based on ferroelectric‐epoxy polymer‐based flake‐free resin coated copper capacitive (RC3) nanocomposites to manufacture multilayer embedded capacitors.

Design/methodology/approach

This paper discusses thin film technology based on RC3 nanocomposites. In particular, recent developments in high capacitance, large area, thin film passives, and their integration in system in a package (SiP) are highlighted.

Findings

A variety of RC3 nanocomposite thin films ranging from 8 to 50 microns thick were processed on copper substrates by liquid coating. Multilayer embedded capacitors resulted in high capacitances of 16‐28 nF. The fabricated test vehicle also included two embedded resistor layers with resistances in the range of 15 Ω to 100 kΩ. To enable high performance devices, an embedded resistor must meet certain tolerances. The embedded resistors can be laser trimmed to a tolerance of <5 percent, which is usually acceptable for most applications. An extended embedded passives solution has been demonstrated, both through its high wireability designs and package performance, to be perfectly suited for SiP applications.

Research limitations/implications

This case study designed and fabricated an eight layer high density internal passive core and subsequently applied fine geometry three buildup layers to form a 3‐8‐3 structure. The passive core technology is capable of providing up to six layers of embedded capacitance and could be extended further.

Originality/value

A thin film technology based on ferroelectric‐epoxy polymer‐based flake‐free RC3 nanocomposites was developed to manufacture multilayer embedded capacitors. The overall approach lends itself to package miniaturization because capacitance can be increased through multiple layers and reduced thickness to give the desired values in a smaller area.

Details

Circuit World, vol. 35 no. 4
Type: Research Article
ISSN: 0305-6120

Keywords

Article
Publication date: 8 February 2011

Rabindra N. Das, How T. Lin, John M. Lauffer and Voya R. Markovich

There has been increasing interest in the development of printable electronics to meet the growing demand for low‐cost, large‐area, miniaturized, flexible and lightweight devices…

1192

Abstract

Purpose

There has been increasing interest in the development of printable electronics to meet the growing demand for low‐cost, large‐area, miniaturized, flexible and lightweight devices. The purpose of this paper is to discuss the electronic applications of novel printable materials.

Design/methodology/approach

The paper addresses the utilization of polymer nanocomposites as it relates to printable and flexible technology for electronic packaging. Printable technology such as screen‐printing, ink‐jet printing, and microcontact printing provides a fully additive, non‐contacting deposition method that is suitable for flexible production.

Findings

A variety of printable nanomaterials for electronic packaging have been developed. This includes nanocapacitors and resistors as embedded passives, nanolaser materials, optical materials, etc. Materials can provide high‐capacitance densities, ranging from 5 to 25 nF/in2, depending on composition, particle size, and film thickness. The electrical properties of capacitors fabricated from BaTiO3‐epoxy nanocomposites showed a stable dielectric constant and low loss over a frequency range from 1 to 1,000 MHz. A variety of printable discrete resistors with different sheet resistances, ranging from ohm to Mohm, processed on large panels (19.5×24 inches) have been fabricated. Low‐resistivity materials, with volume resistivity in the range of 10−4‐10−6 ohm cm, depending on composition, particle size, and loading, can be used as conductive joints for high‐frequency and high‐density interconnect applications. Thermosetting polymers modified with ceramics or organics can produce low k and lower loss dielectrics. Reliability of the materials was ascertained by (Infrared; IR‐reflow), thermal cycling, pressure cooker test (PCT) and solder shock testing. The change in capacitance after 3× IR‐reflow and after 1,000 cycles of deep thermal cycling between −55°C and +125°C was within 5 per cent. Most of the materials in the test vehicle were stable after IR‐reflow, PCT, and solder shock.

Research limitations/implications

The electronic applications of printable, high‐performance nanocomposite materials such as adhesives (both conductive and non‐conductive), interlayer dielectrics (low‐k, low‐loss dielectrics), embedded passives (capacitors and resistors), and circuits, etc.. are discussed. Also addressed are investigations of printable optically/magnetically active nanocomposite and polymeric materials for fabrication of devices such as inductors, embedded lasers, and optical interconnects.

Originality/value

A thin film printable technology was developed to manufacture large‐area microelectronics with embedded passives, Z‐interconnects and optical waveguides, etc. The overall approach lends itself to package miniaturization because multiple materials and devices can be printed in the same layer to increase functionality.

Details

Circuit World, vol. 37 no. 1
Type: Research Article
ISSN: 0305-6120

Keywords

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