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Manufacture and characterization of elastic interconnection microstructures in silicone elastomer
KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

The subject of this thesis is a new chip to substrate interconnection technique using self-aligning elastic chip sockets. This work was focused on the technology steps which are necessary to fulfill in order to realize the suggested technique. Elastic chip sockets offer a solution for several assembly and packaging challenges, such a thermo-mechanical mismatch, effortless rework, environmental compatibility, high interconnection density, high frequency signal integrity, etc.

Two of the most challenging technology aspects, metallization and etching of the silicone elastomer were studied, but also, air bubble free casting of the silicone elastomer was taken into consideration. Elastic chip sockets and single elastic micro-bump contacts of different shapes and sizes were manufactured and characterized.

The contact resistance measurements revealed that the elastic micro-bump contacts manufactured by using the developed methods require less than one tenth of the contact force to achieve the same low contact resistance as compared to commercial elastic interconnection structures.

The analysis and measurements of the high frequency properties of the elastic micro-bump structures have shown that they can operate up to several tens of GHz without a serious degradation of the signal quality.

The same methods were applied to manufacture very high density contact area array (approximately 80000 connections/cm2), which until now was achieved only using so called chip-first techniques.

The low contact resistance, the absence of environmentally harmful materials, no need of soldering, easy rework as well as capability of very high interconnecting density and very high frequency compatibility, indicates a high potential of this technique for assembly and packaging.

Moreover, the presented technology of the silicone elastomer micromachining (metallization and RIE in particular) can be used for manufacturing of other microstructures, like chemical or biological micro reactors.

Place, publisher, year, edition, pages
Stockholm: KTH , 2006. , xiv, 47 p.
Series
Trita-EKT, ISSN 1650-8599 ; 2006:1
Keyword [en]
silicone elastomer, packaging, assembly, elastic interconnection, chip socket, metallization, RIE of silicone elastomer
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:kth:diva-3877OAI: oai:DiVA.org:kth-3877DiVA: diva2:9840
Public defence
2006-03-23, Sal Q221, Mittuniversitet, Östersund, 13:00
Opponent
Supervisors
Note
QC 20110114Available from: 2006-03-14 Created: 2006-03-14 Last updated: 2011-01-14Bibliographically approved
List of papers
1. Sputter Deposing of Chromium, Gold and Copper on Silicone Elastomer
Open this publication in new window or tab >>Sputter Deposing of Chromium, Gold and Copper on Silicone Elastomer
(English)In: IEEE transactions on components and packaging technologies (Print), ISSN 1521-3331, E-ISSN 1557-9972Article in journal (Other academic) Submitted
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-5457 (URN)
Note
QS 20120326Available from: 2006-03-14 Created: 2006-03-14 Last updated: 2017-11-21Bibliographically approved
2. CF4/O2 versus SF6/O2 RIE of Silicon Elastomer: Characterization and Comparison
Open this publication in new window or tab >>CF4/O2 versus SF6/O2 RIE of Silicon Elastomer: Characterization and Comparison
(English)In: IEEE transactions on components and packaging technologies (Print), ISSN 1521-3331, E-ISSN 1557-9972Article in journal (Other academic) Submitted
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-5458 (URN)
Note
QS 20120326Available from: 2006-03-14 Created: 2006-03-14 Last updated: 2017-11-21Bibliographically approved
3. Metal Covered Elastic Micro-Bump Contacts as an Alternative to Commercial Elastic Interconnection Techniques
Open this publication in new window or tab >>Metal Covered Elastic Micro-Bump Contacts as an Alternative to Commercial Elastic Interconnection Techniques
(English)In: IEEE transactions on components and packaging technologies (Print), ISSN 1521-3331, E-ISSN 1557-9972Article in journal (Other academic) Submitted
Abstract [en]

In this work, a novel chip-to-board interconnection structure have been manufactured, and some of its characteristics have been investigated. This chip connection technique can for instance serve as a FCOB (Flip Chip on Board) technique, for connecting test equipments during testing bare chip on wafer, and with some more development, in three dimensional multi chip modules. A setup of elastic micro-bumps was cast, metal covered, patterned, and electro-mechanically characterized. The metal-covered silicon elastomer contact-structures were manufactured on FR-4 carrier-plates. Visual inspection of the micro-bumps was conducted in a SEM (Scanning Electron Microscope). The electro-mechanical properties were measured by simultaneous use of a DMA (Dynamic Mechanical Analyzer) and a Kelvin Bridge structure for resistance measurement. The measurements gave the micro-bump to chip resistance behavior as a function of the micro-bump deflection distance and applied mechanical force when direct current was applied. The results obtained from the measurements have revealed that such a technique requires less than one tenth of the mechanical contact force for achieving the contact resistance of the same magnitude as for commercial elastic interconnection techniques. This would be of significant advantage because the amount of electrical contacts per unit of area has tendency of continued growth.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-5459 (URN)
Note
QS 20120326Available from: 2006-03-14 Created: 2006-03-14 Last updated: 2017-11-21Bibliographically approved
4. Manufacturing of Via Holes in Silicon Elastomer
Open this publication in new window or tab >>Manufacturing of Via Holes in Silicon Elastomer
(English)In: IEEE transactions on components and packaging technologies (Print), ISSN 1521-3331, E-ISSN 1557-9972Article in journal (Refereed) Accepted
Identifiers
urn:nbn:se:kth:diva-5460 (URN)
Note
QC 20110114Available from: 2006-03-14 Created: 2006-03-14 Last updated: 2017-11-21Bibliographically approved
5. Elastomer Chip Sockets for Reduced Thermal Mismatch Problems and Effortless Chip Replacement, Preliminary Investigations
Open this publication in new window or tab >>Elastomer Chip Sockets for Reduced Thermal Mismatch Problems and Effortless Chip Replacement, Preliminary Investigations
2003 (English)In: IEEE Transactions on Advanced Packaging, ISSN 1521-3323, E-ISSN 1557-9980, Vol. 26, no 1, 33-40 p.Article in journal (Refereed) Published
Abstract [en]

To avoid the problem with thermo-mechanical stress induced fatigue using conventional flip-chip mounting of bare chips, an elastic chip socket has been developed.

The socket is made by casting silicone elastomer into micro structured silicon molds to form micro bump arrays. After the elastomer is cured and released from the mold, a metal layer is deposited and patterned.

A chip is placed in the socket utilizing guiding structures for chip self alignment. The chip is then held in place by a spring loaded back-plate which can also serve as a heat sink for highly effective chip cooling. Since no adhesives, underfills or solders are used, the rework process becomes very simple and it can also be repeated many times for-the same socket.

Initial contact resistance and thermo-mechanical robustness measurements indicates that this type of sockets could work as a superior replacement for conventional flip-chip technologies in many applications. The particular design of the contact bumps results in metal structures that resemble (although up side down) and are scalable as those in the Chip-First technology. Preliminary thermal shock experiments from room temperature to liquid nitrogen and back show good survival. Thus, this new chip interconnect method indicates the possibility of getting the advantages of the Chip-First technology while eliminating the demand of placing the chip first. The concept will work for chips with rim positioned pads as well as for high density area arrays.

Keyword
chip-first; chip socket; flip chip; multi-chip modules; packaging; silicone elastomer; thermal fatigue; thermal stress
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-5461 (URN)10.1109/TADVP.2003.811362 (DOI)000182870300005 ()
Note
QC 20110114Available from: 2006-03-14 Created: 2006-03-14 Last updated: 2017-11-21Bibliographically approved
6. Very High Density Interconnect Elastomer Chip Sockets
Open this publication in new window or tab >>Very High Density Interconnect Elastomer Chip Sockets
2006 (English)In: IEEE Transactions on Advanced Packaging, ISSN 1521-3323, E-ISSN 1557-9980, Vol. 29, no 2, 202-210 p.Article in journal (Refereed) Published
Abstract [en]

The integration of more and more functionality into smaller and smaller form factor electronic products, drives the need for denser chip to substrate interconnect systems. As the number of I/O pins increases, the use of area array chips or packages becomes inevitable. Metal patterned elastomer chip sockets have now been improved to work with contact densities as high as 80000 contacts/cm(2) corresponding to a pitch of 36 mu m. Sockets with 10000 contacts and a 72-mu m pitch have survived more than 400 cycles in air-to-air thermal cycling chambers as well as freezing shocks caused by dipping into liquid nitrogen. Although the daisy chain test circuits breaks for temperatures lower than -50 degrees C and higher than 90 degrees C, they always return to the initial resistance values when entering the normal temperature range. The combination of a gold-to-gold contact interface and the elastic features of the contact bumps makes this socket an ideal compliance layer between bare chips and different types of carrier substrates, reducing the problems caused by thermomechanical mismatch between the substrate and the chip. Bad dies can easily be replaced, since the chip is not soldered or glued to the socket. The size and the possibility to control the geometry of the contacts provides means to maintain a good high-frequency characteristic impedance matching all the way to the chip pad.

Keyword
chip-first, chip socket, flip-chip, high-density interconnect, multichip modules, packaging, silicone elastomer, thermal fatigue, thermal stress
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-5462 (URN)10.1109/TADVP.2006.871178 (DOI)000237429900001 ()2-s2.0-33646534157 (Scopus ID)
Note
QC 20110114Available from: 2006-03-14 Created: 2006-03-14 Last updated: 2017-11-21Bibliographically approved
7. High Frequency Signal Transmission Properties of Elastomer Chip Sockets
Open this publication in new window or tab >>High Frequency Signal Transmission Properties of Elastomer Chip Sockets
(English)Article in journal (Refereed) Accepted
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-5463 (URN)
Note
QC 20110114Available from: 2006-03-14 Created: 2006-03-14 Last updated: 2011-01-14Bibliographically approved
8. Solder and Adhesive Free Chip Assembly Using Elastic Chip Sockets: Concept, Manufacture and Preliminary Investigation
Open this publication in new window or tab >>Solder and Adhesive Free Chip Assembly Using Elastic Chip Sockets: Concept, Manufacture and Preliminary Investigation
2004 (English)In: Proceedings of 2004 International IEEE Conference on the Asian Green Electronics (AGEC), 2004, 12-17 p.Conference paper, Published paper (Refereed)
Abstract [en]

Flip Chip connections enormously reduces the amount of solder as compared to mounting packaged devices, apart from also offering superior high frequency properties and placement density. However, when assembling chips to substrates having different thermal expansion coefficient, the solder balls are exposed to strain, the more so the denser the connections (and consequently smaller balls), and the higher the power densities, resulting in wider temperature cycles. This will usually result in loss of contact reliability. Using other materials than solder or using underfills may partially improve the situation, but causes other problems. In order to test another concept maintaining or exceeding the excellent HF and density properties of conventional Flip Chip, while practically eliminating the thermal mismatch problems and providing effortless chip replacement, the Elastic Chip Socket was developed. Silicone elastomer was molded in a precision mold made using anisotropic etching of Si. These structures were subsequently metallized and the metal patterned using electro plated resist. So far functional chip sockets with pin densities of 45 000 pins per cm2 (22 500 simultaneously functional connections to a 7 × 7 mm die) and more have been achieved which endure multiple repeated matings and quick temperature cycling between - 40°C and + 90°C. The following is a summary of the group's achievement this far, Oct. 2003.

National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-5464 (URN)10.1109/AGEC.2004.1290858 (DOI)078038203X (ISBN)
Conference
2004 International IEEE Conference on Asian Green Electronics (AGEC); Hong Kong; 5 January 2004 through 9 January 2004
Note
QC 20110114Available from: 2006-03-14 Created: 2006-03-14 Last updated: 2011-01-14Bibliographically approved
9. Method for Making Micro/Nano-Liter Pools and Channels with Hydrophilic Bottom in Silicone Elastomer on Glas
Open this publication in new window or tab >>Method for Making Micro/Nano-Liter Pools and Channels with Hydrophilic Bottom in Silicone Elastomer on Glas
(English)Article in journal (Other academic) Submitted
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-5465 (URN)
Note
QS 20120327Available from: 2006-03-14 Created: 2006-03-14 Last updated: 2012-03-27Bibliographically approved
10. Contact Resistance of Thin Film Metal Contacts
Open this publication in new window or tab >>Contact Resistance of Thin Film Metal Contacts
2006 (English)In: IEEE transactions on components and packaging technologies (Print), ISSN 1521-3331, E-ISSN 1557-9972, Vol. 29, no 2, 371-378 p.Article in journal (Refereed) Published
Abstract [en]

To be able to reduce the size of products having electronic devices, it becomes more and more important to miniaturize the electromechanical parts of the system. The use of micromechanical connectors and contact structures implies the need of methods for estimating the properties of such devices. This work will, by use of finite element modeling, treat the influence of a thin film constituting at least one of the contacting members of an electrical contact. The error introduced by using the traditional Maxwell/Holm contact constriction resistance theory will be investigated. Numerical methods are used to present a way to approximate the total resistance for the thin metal film contact.

Keyword
constriction resistance, contact resistance, Holm resistance, Maxwell resistance, microelectromechanical system (MEMS) relay, metal film, microconnector, microrelay, Sharvin resistance
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-5466 (URN)10.1109/TCAPT.2006.875891 (DOI)000237982600020 ()2-s2.0-33744831222 (Scopus ID)
Note
QC 20110114Available from: 2006-03-14 Created: 2006-03-14 Last updated: 2017-11-21Bibliographically approved

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Citation style
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Output format
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