4 research outputs found
Thermal and electrical modelling of polymer cored BGA interconnects
Polymer cored BGA/CSP balls have been proposed as
a more reliable alternative to solid solder balls for
demanding application environments. Their potential
advantages are dependant on their increased compliance
compared with a solid solder ball, thereby reducing the
level of stress imposed on the solder joints during
exposure to cyclic thermal loads and impacts. The latter is
of particular importance for hand held products
assembled using lead free solders, which are much more
brittle than traditional tin-lead alloys, but this may also be
important for harsh environment applications where tinlead
solders are still being used, such as in aerospace and
defence electronics applications. The increased
compliance of a polymer cored ball may reduce the
requirement for underfilling of components in hand held
products, and allow adoption of BGA/CSP for safety
critical applications in harsh environments. Such polymer
cored interconnects are however likely to provide a
reduced thermal and electrical conductivity and it is
important to ensure any such effects do not impact upon
the thermal and electrical performance of the product.
This paper utilises analytical and computational
modelling techniques to achieve an understanding of the
effect of conductor particle geometry and properties on
thermal and electrical performance. Such models offer a
route to appropriate materials selection for the polymer
spheres and their conductive coatings, and for
establishing optimum design parameters such as ball
diameter, conductive coating thickness, solder pad
diameter, and solder volumes.
The results confirm that the introduction of polymer
cored BGA balls will result in some increases in thermal
and electrical resistance, but that these changes will have
minor impacts on the overall performance of products
Thermal and electrical modelling of polymer cored BGA interconnects
Polymer cored BGA/CSP balls have been proposed as
a more reliable alternative to solid solder balls for
demanding application environments. Their potential
advantages are dependant on their increased compliance
compared with a solid solder ball, thereby reducing the
level of stress imposed on the solder joints during
exposure to cyclic thermal loads and impacts. The latter is
of particular importance for hand held products
assembled using lead free solders, which are much more
brittle than traditional tin-lead alloys, but this may also be
important for harsh environment applications where tinlead
solders are still being used, such as in aerospace and
defence electronics applications. The increased
compliance of a polymer cored ball may reduce the
requirement for underfilling of components in hand held
products, and allow adoption of BGA/CSP for safety
critical applications in harsh environments. Such polymer
cored interconnects are however likely to provide a
reduced thermal and electrical conductivity and it is
important to ensure any such effects do not impact upon
the thermal and electrical performance of the product.
This paper utilises analytical and computational
modelling techniques to achieve an understanding of the
effect of conductor particle geometry and properties on
thermal and electrical performance. Such models offer a
route to appropriate materials selection for the polymer
spheres and their conductive coatings, and for
establishing optimum design parameters such as ball
diameter, conductive coating thickness, solder pad
diameter, and solder volumes.
The results confirm that the introduction of polymer
cored BGA balls will result in some increases in thermal
and electrical resistance, but that these changes will have
minor impacts on the overall performance of products
Novel processes to enable deposition of metal coated polymer micro-spheres for flip-chip interconnections
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
Electrical properties of an isotropic conductive adhesive filled with silver coated polymer spheres
In the present study the electrical performance of newly developed epoxy resin based Isotropic Conductive Adhesives (ICAs) filled with silver coated mono sized polymer spheres have been investigated and compared with conventional solid silver particle/flake filled ICAs. The effects of particle size on the volume resistivity and percolation threshold of the new ICA have been studied. Two different diameters, i.e. 30μm and 4.8 μm, of silver coated mono sized spherical polymer particles have been used in this study. The results show that, for the same volume fraction, the volume resistivity of the adhesive with 4.8μm particles is lower than that with 30μm particles. The adhesive formulated with 4.8μm particles also exhibits a lower percolation threshold than that with 30μm particles. The resistivity of the adhesive containing 4.8μm particles was found to be of same order as that of currently commercially available ICAs, but with a significantly reduced silver content