14th European Microelectronics and Packaging Conference & Exhibition Friedrichshafen, Germany, 23-25 June 2003

NEW INDUSTRIAL APPLICATIONS IN 3-D INTERCONNECTION Authors : Christian Val/3D Plus, Olivier Lignier/3D Plus Nick Chandler/BAe systems UK, Andrea Pizzato/FIAT Italie, Jean-Yves Deletage/IXL University France, Yves Ousten/IXL University France, Christiane Faure/Solectron France, Alexandre Val/Solectron France

Abstract 3-D interconnection technologies are now becoming mature. A general panorama of all actors manufacturing 3-D modules will be quickly presented. The particularities of the 3-D technology developed by 3D PLUS and recently integrated into a Framework 5 R&T project will be described. This EC project is called VIGOR for Vertical InteGration for Opto and Radio (sub)systems. Thanks to the work performed by the consortium, constituted by SOLECTRON for volume production part, CRF (FIAT) and BAE SYSTEMS end-users, the performance of the 3-D module will be significantly improved. The applications proposed by CRF will include the stacking of a wireless module for automotive, integrating digital levels and a high-frequency level. The applications developed by BAE SYSTEMS will integrate opto-electronics functions, i.e. containing optical and opto-electronic parts as well as electronics To the best of our knowledge, no 3-D module supplier proposes these types of applications. As scientific support, Bordeaux University – IXL Laboratory will carry out thermomechanical simulations which are very crucial.. This technico-industrial approach is quite ambitious as it couples automotive and avionics applications specialists with the number one worldwide for surface-mounting manufacturing and a small company, 3D PLUS, which has already two production lines, one for high-reliability, the other for the industrial market • Hot process : the temperature is higher than 150°C.

Table 1 : Classification of 3D technologies (see end of the document)

1. 3-D Technology 1. 1 Introduction - overview of 3-D Module at present 3-D interconnection left “the niches” with which it started to reach volume productions. This led to a race for modules thinning, which in fine leads to a very significant cost decrease. The 3-D various techniques are reviewed with their specificities ; they are compared to those of 3D Plus.

1.2 Generalities on 3-D interconnection technologies Since a few years, new interconnections in 3-dimension technologies have appeared, most of them pulled by mobiles telephone markets. In order to position and compare them, we propose a new classification of all the 3-D interconnection technologies (see table 1). The 3-D interconnection, which was first developed to stack memories, is progressively applied to the stacking of heterogeneous components (active and passive components) in order to build Systems in Package. An important differentiation in the processes used for the interconnection is given and driven by the maximal temperature of the process : •

Cold process : the temperature is inferior to 150 °C

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“Hot” process : This process is used by most of the companies which stack packaged dice (TSOP, µBGA, CSP) : Dense Pak, Staktek, Simple Technology, Amkor, Samsung, Mitsubishi, etc...Some others use flip chip bare dice, mounted on a substrate. This necessitates high temperature reflows as well (NEC and NASDA). Those who use a folded flex, like Tessera and Valtronic, mount flip chip or micro BGA by reflow and will be forced, because of the coming of leadless soldering to use alloys at a much higher temperature. We can observe that the interconnection technique which is based on a dipping in a soldering bath or on a furnace reflow soldering, will considerably penalize these companies, since the coming of leadless soldering significantly increase the melting temperatures (between 30 and 40°C). As a consequence, these companies will be forced to use solder alloys with higher melting temperatures in order to avoid their reflow during the mounting of the cubes on the PCB by their customers, thus leading to having working peak temperatures inside the reflow furnace comprised between 280 and 300°C ; this will significantly weaken the components and sometimes even be unacceptable. These companies should launch a new interconnection technique to overcome this difficulty. “Cold” process : This is the most used by the companies which work with chip on chip bare dice. For the time

14th European Microelectronics and Packaging Conference, Friedrichshafen, Germany, 23-25 June 2003 being, this technique is limited to the stacking of memories; it does not allow the stacking of heterogeneous components (like memories, µprocessors, passive components) and is limited in frequencies.

. Electrical tests of each level, in order to get an excellent yield and use commercial die . “Cold” process 3D PLUS interconnection technique comprises 6 main steps (as a comparison, there are 20 to 25 steps with some other companies). -

Figure 1 : Cold process

Figure 1 : stacking of dice without die to die interconnection Three companies use the cold process according to two techniques : • Conductive glue, like TRW/VCI • Bus metal, like 3D Plus and Irvine Sensors These two companies (3D Plus and Irvine Sensors) can stack any kind of components in order to build real Systems in Package.

The Chip on tape is well known. It allows using tapes, generally with one level, sometimes with two levels, exceptionally with four levels, in the case of very quick signals, but the pitch of the conductors necessitated by these printed packages can still be easily done ; this is not the case with the new folded packages which necessitate flex with extremely small pitches (around 50 microns) ; the electrical adaptation of such packages is difficult and the variations in the velocity of propagation lead to very difficult problems. The moulding of the components allows to protect them ; many companies stack the components without moulding the 3-D cube : Dense-Pack, stack-Tech, Simple Technology, NEC, Tessera, Valtronic. Another advantage of the moulding is that it prevents the penetration of soldering flux and of all outside substances such as dust which, linked to humidity can develop leakage current. Leadless solder alloys lead to high reflow temperature and the flux is more and more difficult to remove at the level of the PCB. After mounting, when the PCB is cleaned, the flux could penetrate inside the non-moulded cube. Plating allows 3D PLUS, like Irvine Sensors, to interconnect the different levels between them, by using the shortest path. These metallic bus have a very low electrical resistance and a very low inductance. This is what makes 3D PLUS different with regards both the Chip-On-Chip techniques (length of wires could be up to 6 to 7 mm) and the folded packages.

Figure 2 : Bus metal process

Laser direct patterning constitutes a significant technical advantage in terms of cost, since with a unique etching operation, (beam speed : around 3 meters per second), it is possible to perform what is generally done in 5 operations when a photo etching is used.

1.3. 3-D INTERCONNECTION CHARACTERISTICS COMPARED TO 3D PLUS CHARACTERISTICS The specific advantages of 3D PLUS technology are presented, compared to the competition technologies. 1.3.1

Chip on Tape Stacking/moulding with Epoxy resin Cutting with dicing machines Plating : this technology is around 50 years old and is perfectly mastered – it is the PCB technology. Laser Direct Patterning Final electrical test

2. The aims of the VIGOR project

Manufacturing process

The aims of VIGOR, a collaborative project under the European Framework 5 Programme, are :

. Cost of raw material as low as possible

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14th European Microelectronics and Packaging Conference, Friedrichshafen, Germany, 23-25 June 2003 • Develop a robust and versatile, novel module technology combining the advantages of System-inPackage integration with vertical integration and allowing the use of any kind of active and passive components • Provide industrial capabilities for high integration of various functions, particularly opto-electronic and wireless, in a cost-effective module, manufacturable in volume • Design and build validation prototypes having optoelectronic or wireless functions. The major task will consist in improving the basic technology steps with the view to future volume manufacturing. The drawing hereafter helps for better understanding : Final testing

Flex, flex-rigid or rigid substrates

Laser structuring for connections between levels

Assembly of various components

Ni/Au plating of cube faces

Electrical testing Stacking using special tooling

Epoxy moulding

Sawing cube faces to size

prototype application thanks to the large knowhow of SOLECTRON. From the design validation, assembly of the validation prototypes will be performed. The DFX stands for Design For Assembly (DFA), Design For Test (DFT), Design For Supply Chain (DFSC). All these aspects are very important to achieve high performance, cost-effective solutions for volume manufacturing. Several advanced tools will be used : . Trilogy (DFA+DFT) : Genesis (Design optimization assistant), Enterprise (PCB design checking), VPL (component analysis versus assembly). . Testway (DFT at schematic level) . DFT report generator (at PCB layout level) . Stendhal (DFSC : a tool developed by Solectron which is linked to powerful data bases). These know-how of Solectron, applied to the manufacturability of the 3-D modules will allow to build modules at very low cost.

4. Applications-driven validation prototypes Two kinds of validation prototype will be designed, manufactured and characterised: one is an optoelectronic application in avionics and the other a wireless application in automotive. Both are intended to demonstrate the viability of the developed technologies to bring performing solutions in their respective fields to their technical and economical requirements. 4.1. Wireless applications

3. The 3-D technology basis for VIGOR The 3-D technology developed by 3D Plus started in 1989 at Thales for Defense and Aerospace applications. 3D Plus was created in 1996 in order to design and manufacture 3-D memory and SiP modules for niche markets such as Space and Medical. A production line was launched in 2002 to penetrate the industrial market. The aim of the cooperation with Solectron is the industrialisation of this process to penetrate big volume markets such as automotive, telecommunication, etc. Additionally to a drastic reduction of the manufacturing costs, the aims of Vigor are to design and manufacture 3-D modules for new applications : - opto-electronics applications in 3-D - wireless applications for automotive Thanks to Vigor project, a very strong collaboration has started between Solectron, one of the biggest manufacturers worldwide for electronic boards, and 3D Plus, a high-tech company with a view to lowering the costs. For that purpose, a DFx, design for manufacturing with validation of mechanical specifications of components vs. PCB design and validation of PCB design conformity, design for test, will be conducted for each validation

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There is growing interest in wireless communication in automotive applications, based presently on different protocols. In fact, Siemens AT has fully developed and put into production on the Megane Scenic a wireless unit for the measurement of the tyre pressure and transmission to the body computer. Nokian Tyres and VTT, among other partners, have developed an intelligent unit based on Bluetooth technology for the measurement of pressure and temperature inside the tyre, monitoring also road surface changes. Commercial applications are targeted for high speed category tyres for vans and high-end passenger cars. During the next years we will face standardisation of wireless protocol / technology in the automotive sector, aimed at the system cost reduction. Finally a piezo-electric system has been used for the measurement of engine oil level/quantity in luxurious DC car: this unit is fully integrated inside the engine oil chamber and the communication toward the engine ECU is realised through radio-frequency local conversion. The automotive application will deal with the design and development of an autonomous general purpose module for wireless communication based on Bluetooth technology. It will be integrated into a three-dimensional structure that will include: the micro-controller for the interface towards the field, the Bluetooth transceiver and the related RF circuitry, the planar antenna and passive components. It will also exhibit ruggedness and reliability typically required for automotive applications. This module will be used in vehicle electronic units in order to

14th European Microelectronics and Packaging Conference, Friedrichshafen, Germany, 23-25 June 2003 replace functions presently implemented by means of physical connections. Power supply functionality will be also investigated, in order to realise a true self-standing unit. This will be accomplished by means of an autonomous energy storage unit, such as battery, radio frequency or kinetic energy concept. These approaches have already been used in the automotive for stand-alone sensors (tyre pressure, oil level / quantity monitoring). Some measurable targets could be preliminarily identified as follows : wiring harness complexity reduction ( cabling and connectors) of about 30% and consequent increase of the vehicle reliability of the same amount reduction of the software development time / cost of about 60% for each new application, as the wireless unit could be easily re-used in different applications . Presently, the mean development time is about 2 years and related cost is in the range of 500 kEuro.

The objective of the opto-electronics validation prototype is to realise a functioning 3D Module which incorporates opto-electronic components and optical I/Os, including, for example, linear arrays of VCSELs and detectors, a means of optical switching or routing, and a method for connecting the optical I/Os to other parts of a system. The signal bandwidth should exceed 1 GHz.

The challenge is to integrate inside a single device a complete class 1 and 2 BlueTooth® system with on-board software in order to avoid managing the uppers layers above the HCI and communicate by the most common interfaces, quicker and more simple than HCI The functional diagram for the opto-electronic part of the dedicated test vehicle is given below. Identification of available and suitable components have been performed. First set of opto-electronic test vehicle is going to be evaluated through environmental tests. The functions included in the BlueTooth® system are : Micro-controller. Memory BlueTooth® baseband controller Radio-frequency transceiver Power amplifier Radio-frequency switch Power management External interface Identification of the available and suitable components for implementing the functions required have been performed following the commercial availability and the size criteria. 4.2. Opto-electronics applications Optics and opto-electronics are already used in products in many market sectors and will be increasingly used at module and board level. In particular, the use of optoelectronic components, modules and sub-systems is anticipated in a growing number of avionics and space applications, such as sensors (e.g. for flight control, fuel metering, safety and security aspects) and passenger services (entertainment, onboard sales, etc.), as well as in automotive, computers, communications and portable equipment. The reasons include high speed / bandwidth, immunity from interference and noise (EMC / EMI / security / safety) and, of course, to handle signals which originate in optical form, e.g. from sensors and in instruments.

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5. Techno-economic aspects Besides the mobile phone sector, automotive and aerospace applications demand an important miniaturisation. This project allows associating in 3-D very heterogeneous components, since they go from high-frequency components to opto-electronics components. The analysis of each cost carried out with a big microelectronics card manufacturer (Solectron) allows targeting these large volume markets. The reduction in weight and volume of the 3-D modules for these applications is at least 10 times. As a matter of fact, cost being a priority objective, the rule is to use standard components only. Almost all these components are packaged (plastic package, TSOP, CSP, etc). Some 3-D approaches exist, as presented in the beginning, called Chip On chip, which are not very much useable for SiP of such complexity (active, passive, optoelectronics, high-frequency components). The versatility of 3D Plus’ 3-D technology associated to its robustness, which is mainly due to moulding, makes this approach the most cost-effective in term of dimension/cost compromise. In order to answer a main tendency with dice thinning and consequently with 3-D modules, a very important study is

14th European Microelectronics and Packaging Conference, Friedrichshafen, Germany, 23-25 June 2003 being carried out with Leti, ST Microelectronics, Thales, Cybernetics, etc.in order to build 3-D modules with 6 levels per mm. (this will reduce the volume of the 3-D modules by another 10 factor). Naturally, this tendency demands the use of bare dice. It is less versatile but we have kept the criteria that made the success of the 3-D technology, i.e.: . Use of standard components (no special die, nor thinned dice) . Electrical test of each level before stacking . Use of moulding (no leakage current) . Signal integrity (use of the power tri-dimensional network concept with embedded vertical and horizontal capacitors). These ultra thin cubes will mainly be dedicated to memories and numeric SiP. For the time being, we have not contemplated the storage of opto-electronics components with this technique. One can think that thanks to these applications and these future developments, the 3-D interconnection will definitively play a major role and that the System in Package concept has itself definitely supplanted the System on Chip.

ACKNOWLEDGEMENTS : We would like to thank the European Community for having accepted to fund this IST project.

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14th European Microelectronics and Packaging Conference & Exhibition Friedrichshafen, Germany, 23-25 June 2003 CLASSIFICATION OF 3-D INTERCONNECTION TECHNOLOGIES

Memories

System-in-Package "SIP" (active, passive components)

HOT Process

COLD Process

Bare die

Packaged die

Soldering

Folded

Soldering

NEC NASDA

Tessera Valtronic

Mitsubishi Sharp Toshiba Fujitsu Samsung IBM Dense Pac Staktec Simple Tech Irvine Sensors Hitachi Cable Legacy

Packaged die

Bare die

Wire bonding

Bus metal 3DPLUS

Chip-on-chip Chip PAC Amkor Sharp Fujitsu ASE Samsung ST Microelectronics Hitachi

Table 1 : Classification of 3D technologies

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Wireless

Chip-to-Chip

Conductive glue

Bus metal

3DPLUS

TRW/ VCI

3DPLUS Irvine Sensors