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Article
Publication date: 1 June 2000

Subhotosh Khan

Permittivity and dissipation factor (Dk and Df) are effects of polarization of different components of the dielectric substrate material when subjected to an electrical field. A…

Abstract

Permittivity and dissipation factor (Dk and Df) are effects of polarization of different components of the dielectric substrate material when subjected to an electrical field. A database of these important design parameters for PWBs has been developed for Thermount RT. Effects of variations in the level of moisture (bone‐dry to completely saturated at various relative humidity levels), testing temperature (room temperature to 120uC) and testing frequencies (1MHz to 1.5GHz) on Dk and Df are reported. As the frequency of test is increased from 1MHz to 1.5GHz, the effect of moisture on the properties is reduced. Comparison with conventional glass/FR4 laminate properties shows the distinct advantage of Thermount. It is increasingly used in high frequency cellular telephone, satellite, and wireless applications which require HDI PWBs to achieve the highest packaging density at the lowest cost and weight.

Details

Circuit World, vol. 26 no. 2
Type: Research Article
ISSN: 0305-6120

Keywords

Article
Publication date: 1 December 2001

Subhotosh Khan and Dan J. Molligan

Personal electronic devices at the user interface, like cell phones, utilize BGA/CSP structure for miniaturization of circuits. These structures are subjected to severe thermal…

Abstract

Personal electronic devices at the user interface, like cell phones, utilize BGA/CSP structure for miniaturization of circuits. These structures are subjected to severe thermal loads due to environment of use. Starting with a microstructure of a failed board due to thermal cycles, the stresses/strains in this structure were analyzed from –408C to 1258C. In the finite element models (ABAQUS), we represented the structure as a composite of three‐dimensional (3‐D) elastic materials. The model showed stress/strain/energy concentrations at the actual failure points. The model also provided a route to improved durability by reducing these failure potentials, through change in the substrate of the printed circuit board (PCB). We observed significant reduction in failure potential when resin coated copper was replaced by THERMOUNT1 in PCB. This improved performance can be directly related to better‐matched modulus and coefficient of thermal expansion (CTE) of the PCB substrate to the chip (silicon). A more sophisticated model is under construction, where the time dependent material properties and non‐linear effects such as solder creep will be included.

Details

Circuit World, vol. 27 no. 4
Type: Research Article
ISSN: 0305-6120

Keywords

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