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Papers by Helge Kristiansen

ABSTRACT In the field of flat panel displays, packaging technology has a significant influence on... more ABSTRACT In the field of flat panel displays, packaging technology has a significant influence on display performance. The electrical interconnect between the LCD and the LCD driver circuit is an area that needs improvement to achieve finer pitch, easier assembly and greater connection reliability. For LCD driver packaging, the ideal assembly process would possess the following characteristics: low processing cost; reliability suitable to the final application; high-density, fine pitch capability; low product profile; acceptable joint resistance; ease of inspection; and reworkability. The overall trend in LCD driver IC packaging has been to move the driver IC closer to the LCD itself. At present, TAB is the predominant packaging approach for large area LCDs. In most cases, the TAB is directly connected to the ITO traces on the glass using anisotropic conductive adhesive (ACA). In chip-on-glass (COG) technology, the driver LSI chips have moved all the way on to the LCD glass itself. COG is typically done by flip chip, also often with the use of conductive adhesives. ITO traces fan out from the IC to the display area, as well as to the point where a polyimide flexible circuit is connected to the glass substrate to supply power and picture information. COG mounting is currently being used in a number of products, in particular when the pixel density is high

The cooling of a silicon tracker at the CERN Large Hadron Collider (LHC) is a demanding task. The... more The cooling of a silicon tracker at the CERN Large Hadron Collider (LHC) is a demanding task. The silicon tracker has to operate at a temperature below 0 C. The small temperature gradients allowed in the tracker volume, as well as the small liquid flow rates allowed, makes the exploitable heat capacity of water marginal. The use of a Binary-Ice{reg{underscore}sign} cooling system is an attempt to address this problem. With the use of a Binary-Ice suspension, a significant improvement in temperature uniformity along a homogeneously heated tube has been observed compared to that of liquid only. This improved uniformity is caused partly by a significantly reduced temperature build-up in the bulk liquid, attributed to the absorbed heat of melting. In addition, the presence of the ice crystals causes the heat transfer coefficient to be superior to similar coolants without ice where the heat transfer coefficient is calculated from the mean liquid temperature.

IEEE Conference Proceedings, 2016

IEEE Conference Proceedings, 2016

Journal of Nanoscience and Nanotechnology, Nov 1, 2010

HAL (Le Centre pour la Communication Scientifique Directe), Feb 1, 2016

Electrical and thermal contact mechanisms in isotropic conductive adhesive (ICA) based on silver ... more Electrical and thermal contact mechanisms in isotropic conductive adhesive (ICA) based on silver coated polymer particles has been investigated. The adhesive conductivities similar of that of traditional silver filled adhesives at less than 10 % of the silver consumption. The high conductivity has been explained by the development of fused metal-metal contacts between neighboring particles.

ABSTRACT This paper presents the results from simulation studies of the mechanical performance of... more ABSTRACT This paper presents the results from simulation studies of the mechanical performance of BGA interconnects based on the use of polymer cored solder balls (PCSBs) as an alternative to the solid solder balls that are typically used. PCSBs have previously been shown to offer improved reliability and this study was performed to improve understanding of the effects of two key PCSB design variables, i.e. metallisation thickness and polymer modulus on their fatigue performance. The results show that minimising the polymer modulus is beneficial in reducing plastic strains in both the solder and copper metallisation on the polymer ball, but that the metallisation thickness has a much less significant effect unless the polymer core modulus is extremely low.

ABSTRACT A metal-coated ball based on a polymer core is under development for chip scale packagin... more ABSTRACT A metal-coated ball based on a polymer core is under development for chip scale packaging (CSP) and ball grid array (BGA) applications. Different polymer cores have been produced and evaluated in order to optimise the mechanical properties of the ball. From a range of candidates with highly diverse properties, a candidate material has been proposed. This decision is based on a combination of a very low thermal expansion coefficient of 25 ppM/0C and E-modulus, which is of the order of 600 MPa.

Journal of Electronic Materials, Feb 27, 2017

Electronics packaging with Anisotropic Conductive Adhesives (ACAs) has been successfully implemen... more Electronics packaging with Anisotropic Conductive Adhesives (ACAs) has been successfully implemented in flat screen assembly and smart cards for more than two decades, but novel processes are required to enable any significant further increases in interconnection density. This paper will report work to further develop two promising methods which can potentially extend the application of the types of conductor particles used in ACAs to enable ultra-fine pitch interconnections by selectively depositing these metal-coated polymer particles onto targeted bond pads. These two methods are electrophoretic deposition (EPD) and magnetic deposition (MD). To allow EPD the particles were positively charged by being immersed in a HCl solution, and then were selectively deposited onto the bumps on a silicon test chip. However the HCl immersion results in etching of the nickel layer, which is believed to significantly impact the conductivity and reliability of the interconnections formed, even though a connection forms between the particles and pads which is quite strong. In the MD process the Ti/Ni/Au bond pads on the test chips were permanently magnetized so that the particles were attracted to the pads, and the results proved that a sufficient density of the Ni/Au coated polymer particles became adhered to the pads providing a simple, low cost, and ultra-fine pitch method.

... 171-175. [6] M. Hussain, A. Nakahira, S. Nishijima, and K. Niihara, "Effects of ... more ... 171-175. [6] M. Hussain, A. Nakahira, S. Nishijima, and K. Niihara, "Effects of coupling agents on the mechanical properties improvement of the TiO2 reinforced epoxy system," Materials Letters, Vol. 26, No 6, April, 1996, pp. 299-303. ...

2003 International Electronic Packaging Technical Conference and Exhibition, Volume 1, 2003

ABSTRACT Models of the anisotropic conductive adhesive assembly process have previously been deve... more ABSTRACT Models of the anisotropic conductive adhesive assembly process have previously been developed. Such models may be used to predict the time for adhesive resin flow out and whether this can be successfully achieved before resin cure. Modelling has also been used to provide significant insights into the effects of component and substrate bond pad geometry on the resin flow distribution and hence on the resulting conductive particle distribution. These models have however only been experimentally validated to a very limited extent. This paper will describe a new experimental technique, which has been developed to allow continuous monitoring of the adhesive thickness throughout the compression process. This technique applies a controlled assembly force through a linear “voice coil” type actuator and the resulting changes in capacitance of the adhesive material can be used to monitor its thickness. The data from tests using this technique show, for example, the effect of the conductor particle stiffness on the rate of adhesive compression during the later stages of the compression process. Such data will be used to further improve more sophisticated models of the ACA assembly process, which will both lead to a better understanding of the process and also facilitate establishment of design rules for different applications.

Physica Scripta, 2004

Porous silicon (PSi) was prepared by electrochemical etching with electrolytes consisting of vari... more Porous silicon (PSi) was prepared by electrochemical etching with electrolytes consisting of various concentrations of HF and dimethylsulphoxide (DMSO) to control the pore size in the range 0.4µm 8µm as measured by scanning electron microscopy. Pool boiling experiments employing resistive heating of samples with a PSi surface in the dielectric cooling liquid FC-72 was performed and compared to samples with a polished Si surface. It was observed that the PSi surface had favorable cooling behavior and yielding the lowest temperature overshoot upon warming up and the lowest surface temperature during boiling by promoting continuous bubble nucleation which again leads to the most efficient heat removal. The results indicate that PSi could favorably be used in cooling of electronic chips. We also present demonstration of the successful fabrication of a Si porous membrane by a onestep electrochemical etching procedure. The onestep etching technique could be used as an alternative method to the standard Si micro machining such as etched by KOH. The PSi membrane could be used for various closed loop two-phase coolers.

Physica Scripta, 2004

Porous silicon (PSi) was prepared by electrochemical etching with electrolytes consisting of vari... more Porous silicon (PSi) was prepared by electrochemical etching with electrolytes consisting of various concentrations of HF and dimethylsulphoxide (DMSO) to control the pore size in the range 0.4µm 8µm as measured by scanning electron microscopy. Pool boiling experiments employing resistive heating of samples with a PSi surface in the dielectric cooling liquid FC-72 was performed and compared to samples with a polished Si surface. It was observed that the PSi surface had favorable cooling behavior and yielding the lowest temperature overshoot upon warming up and the lowest surface temperature during boiling by promoting continuous bubble nucleation which again leads to the most efficient heat removal. The results indicate that PSi could favorably be used in cooling of electronic chips. We also present demonstration of the successful fabrication of a Si porous membrane by a onestep electrochemical etching procedure. The onestep etching technique could be used as an alternative method to the standard Si micro machining such as etched by KOH. The PSi membrane could be used for various closed loop two-phase coolers.

Microelectronics International, 1994

ABSTRACT In the field of flat panel displays, packaging technology has a significant influence on... more ABSTRACT In the field of flat panel displays, packaging technology has a significant influence on display performance. The electrical interconnect between the LCD and the LCD driver circuit is an area that needs improvement to achieve finer pitch, easier assembly and greater connection reliability. For LCD driver packaging, the ideal assembly process would possess the following characteristics: low processing cost; reliability suitable to the final application; high-density, fine pitch capability; low product profile; acceptable joint resistance; ease of inspection; and reworkability. The overall trend in LCD driver IC packaging has been to move the driver IC closer to the LCD itself. At present, TAB is the predominant packaging approach for large area LCDs. In most cases, the TAB is directly connected to the ITO traces on the glass using anisotropic conductive adhesive (ACA). In chip-on-glass (COG) technology, the driver LSI chips have moved all the way on to the LCD glass itself. COG is typically done by flip chip, also often with the use of conductive adhesives. ITO traces fan out from the IC to the display area, as well as to the point where a polyimide flexible circuit is connected to the glass substrate to supply power and picture information. COG mounting is currently being used in a number of products, in particular when the pixel density is high

The cooling of a silicon tracker at the CERN Large Hadron Collider (LHC) is a demanding task. The... more The cooling of a silicon tracker at the CERN Large Hadron Collider (LHC) is a demanding task. The silicon tracker has to operate at a temperature below 0 C. The small temperature gradients allowed in the tracker volume, as well as the small liquid flow rates allowed, makes the exploitable heat capacity of water marginal. The use of a Binary-Ice{reg{underscore}sign} cooling system is an attempt to address this problem. With the use of a Binary-Ice suspension, a significant improvement in temperature uniformity along a homogeneously heated tube has been observed compared to that of liquid only. This improved uniformity is caused partly by a significantly reduced temperature build-up in the bulk liquid, attributed to the absorbed heat of melting. In addition, the presence of the ice crystals causes the heat transfer coefficient to be superior to similar coolants without ice where the heat transfer coefficient is calculated from the mean liquid temperature.

IEEE Conference Proceedings, 2016

IEEE Conference Proceedings, 2016

Journal of Nanoscience and Nanotechnology, Nov 1, 2010

HAL (Le Centre pour la Communication Scientifique Directe), Feb 1, 2016

Electrical and thermal contact mechanisms in isotropic conductive adhesive (ICA) based on silver ... more Electrical and thermal contact mechanisms in isotropic conductive adhesive (ICA) based on silver coated polymer particles has been investigated. The adhesive conductivities similar of that of traditional silver filled adhesives at less than 10 % of the silver consumption. The high conductivity has been explained by the development of fused metal-metal contacts between neighboring particles.

ABSTRACT This paper presents the results from simulation studies of the mechanical performance of... more ABSTRACT This paper presents the results from simulation studies of the mechanical performance of BGA interconnects based on the use of polymer cored solder balls (PCSBs) as an alternative to the solid solder balls that are typically used. PCSBs have previously been shown to offer improved reliability and this study was performed to improve understanding of the effects of two key PCSB design variables, i.e. metallisation thickness and polymer modulus on their fatigue performance. The results show that minimising the polymer modulus is beneficial in reducing plastic strains in both the solder and copper metallisation on the polymer ball, but that the metallisation thickness has a much less significant effect unless the polymer core modulus is extremely low.

ABSTRACT A metal-coated ball based on a polymer core is under development for chip scale packagin... more ABSTRACT A metal-coated ball based on a polymer core is under development for chip scale packaging (CSP) and ball grid array (BGA) applications. Different polymer cores have been produced and evaluated in order to optimise the mechanical properties of the ball. From a range of candidates with highly diverse properties, a candidate material has been proposed. This decision is based on a combination of a very low thermal expansion coefficient of 25 ppM/0C and E-modulus, which is of the order of 600 MPa.

Journal of Electronic Materials, Feb 27, 2017

Electronics packaging with Anisotropic Conductive Adhesives (ACAs) has been successfully implemen... more Electronics packaging with Anisotropic Conductive Adhesives (ACAs) has been successfully implemented in flat screen assembly and smart cards for more than two decades, but novel processes are required to enable any significant further increases in interconnection density. This paper will report work to further develop two promising methods which can potentially extend the application of the types of conductor particles used in ACAs to enable ultra-fine pitch interconnections by selectively depositing these metal-coated polymer particles onto targeted bond pads. These two methods are electrophoretic deposition (EPD) and magnetic deposition (MD). To allow EPD the particles were positively charged by being immersed in a HCl solution, and then were selectively deposited onto the bumps on a silicon test chip. However the HCl immersion results in etching of the nickel layer, which is believed to significantly impact the conductivity and reliability of the interconnections formed, even though a connection forms between the particles and pads which is quite strong. In the MD process the Ti/Ni/Au bond pads on the test chips were permanently magnetized so that the particles were attracted to the pads, and the results proved that a sufficient density of the Ni/Au coated polymer particles became adhered to the pads providing a simple, low cost, and ultra-fine pitch method.

... 171-175. [6] M. Hussain, A. Nakahira, S. Nishijima, and K. Niihara, "Effects of ... more ... 171-175. [6] M. Hussain, A. Nakahira, S. Nishijima, and K. Niihara, "Effects of coupling agents on the mechanical properties improvement of the TiO2 reinforced epoxy system," Materials Letters, Vol. 26, No 6, April, 1996, pp. 299-303. ...

2003 International Electronic Packaging Technical Conference and Exhibition, Volume 1, 2003

ABSTRACT Models of the anisotropic conductive adhesive assembly process have previously been deve... more ABSTRACT Models of the anisotropic conductive adhesive assembly process have previously been developed. Such models may be used to predict the time for adhesive resin flow out and whether this can be successfully achieved before resin cure. Modelling has also been used to provide significant insights into the effects of component and substrate bond pad geometry on the resin flow distribution and hence on the resulting conductive particle distribution. These models have however only been experimentally validated to a very limited extent. This paper will describe a new experimental technique, which has been developed to allow continuous monitoring of the adhesive thickness throughout the compression process. This technique applies a controlled assembly force through a linear “voice coil” type actuator and the resulting changes in capacitance of the adhesive material can be used to monitor its thickness. The data from tests using this technique show, for example, the effect of the conductor particle stiffness on the rate of adhesive compression during the later stages of the compression process. Such data will be used to further improve more sophisticated models of the ACA assembly process, which will both lead to a better understanding of the process and also facilitate establishment of design rules for different applications.

Physica Scripta, 2004

Porous silicon (PSi) was prepared by electrochemical etching with electrolytes consisting of vari... more Porous silicon (PSi) was prepared by electrochemical etching with electrolytes consisting of various concentrations of HF and dimethylsulphoxide (DMSO) to control the pore size in the range 0.4µm 8µm as measured by scanning electron microscopy. Pool boiling experiments employing resistive heating of samples with a PSi surface in the dielectric cooling liquid FC-72 was performed and compared to samples with a polished Si surface. It was observed that the PSi surface had favorable cooling behavior and yielding the lowest temperature overshoot upon warming up and the lowest surface temperature during boiling by promoting continuous bubble nucleation which again leads to the most efficient heat removal. The results indicate that PSi could favorably be used in cooling of electronic chips. We also present demonstration of the successful fabrication of a Si porous membrane by a onestep electrochemical etching procedure. The onestep etching technique could be used as an alternative method to the standard Si micro machining such as etched by KOH. The PSi membrane could be used for various closed loop two-phase coolers.

Physica Scripta, 2004

Porous silicon (PSi) was prepared by electrochemical etching with electrolytes consisting of vari... more Porous silicon (PSi) was prepared by electrochemical etching with electrolytes consisting of various concentrations of HF and dimethylsulphoxide (DMSO) to control the pore size in the range 0.4µm 8µm as measured by scanning electron microscopy. Pool boiling experiments employing resistive heating of samples with a PSi surface in the dielectric cooling liquid FC-72 was performed and compared to samples with a polished Si surface. It was observed that the PSi surface had favorable cooling behavior and yielding the lowest temperature overshoot upon warming up and the lowest surface temperature during boiling by promoting continuous bubble nucleation which again leads to the most efficient heat removal. The results indicate that PSi could favorably be used in cooling of electronic chips. We also present demonstration of the successful fabrication of a Si porous membrane by a onestep electrochemical etching procedure. The onestep etching technique could be used as an alternative method to the standard Si micro machining such as etched by KOH. The PSi membrane could be used for various closed loop two-phase coolers.

Microelectronics International, 1994

A newly initiated effort in research on Green Electronics has resulted in recent advances in the ... more A newly initiated effort in research on Green Electronics has resulted in recent advances in the collaboration between China and Europe. The effort was initiated with the research project EC-GEPRO (Europe-China Cooperation in Green Electronics Production Research). This is funded by the European Commission and engages actors and stimulates high-level debates and cooperation on the development of Green Electronics. This is done through co-organising as well as evaluating the 2nd International Eco-electronics conferences December 7-8, 2006 in Beijing. An evaluation of this conference was carried out by the project, and important issues for improving future collaborative efforts of similar type were identified. In addition to expressing concerns about language and culture gaps, survey respondents placed particular emphasis on the lack of international networks and contacts as a barrier to further international collaboration, whilst suggesting possible ways of overcoming the various obstacles. In addition, the project has co-organised the IEEE CPMT symposium on Green Electronics in Gothenburg on May 23-24 2007.

Proceedings of International Symposium on High Density Packaging and Microsystem Integration 2007, HDP'07, Jun 26, 2007

A newly initiated effort in research on Green Electronics has resulted in recent advances in the ... more A newly initiated effort in research on Green Electronics has resulted in recent advances in the collaboration between China and Europe. The effort was initiated with the research project EC-GEPRO (Europe-China Cooperation in Green Electronics Production Research). This is funded by the European Commission and engages actors and stimulates high-level debates and cooperation on the development of Green Electronics. This is done through co-organising as well as evaluating the 2nd International Eco-electronics conferences December 7-8, 2006 in Beijing. An evaluation of this conference was carried out by the project, and important issues for improving future collaborative efforts of similar type were identified. In addition to expressing concerns about language and culture gaps, survey respondents placed particular emphasis on the lack of international networks and contacts as a barrier to further international collaboration, whilst suggesting possible ways of overcoming the various obstacles. In addition, the project has co-organised the IEEE CPMT symposium on Green Electronics in Gothenburg on May 23-24 2007.