| 1. |
- Hesselblom, Hjalmar, et al.
(författare)
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Very High Density Interconnect Elastomer Chip Sockets
- 2006
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Ingår i: IEEE Transactions on Advanced Packaging. - 1521-3323 .- 1557-9980. ; 29:2, s. 202-210
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 2. |
- Hesselbom, Hjalmar, et al.
(författare)
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Solder and Adhesive Free Chip Assembly Using Elastic Chip Sockets: Concept, Manufacture and Preliminary Investigation
- 2004
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Ingår i: Proceedings of 2004 International IEEE Conference on the Asian Green Electronics (AGEC). - Piscataway, NJ, USA : IEEE. - 078038203X ; , s. 12-17
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 3. |
- Norberg, Gunnar, et al.
(författare)
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Contact Resistance of Thin Film Metal Contacts
- 2006
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Ingår i: IEEE transactions on components and packaging technologies (Print). - 1521-3331 .- 1557-9972. ; 29:2, s. 371-378
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 4. |
- Norberg, Gunnar, et al.
(författare)
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Elastomer Chip Sockets for Reduced Thermal Mismatch Problems and Effortless Chip Replacement, Preliminary Investigations
- 2003
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Ingår i: IEEE Transactions on Advanced Packaging. - 1521-3323 .- 1557-9980. ; 26:1, s. 33-40
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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