Thermal performance of tape based ball grid array over molded packages

Thermal performance of a three chip, overmolded wire-bonded plastic ball grid array (WB-PBGA) package with four layer substrate attached to a 1.52-mm-thick, four-layer (2s2p), FR4 printed wiring board (PWB) has been evaluated under horizontal natural convection conditions for underhood automotive applications as a function of ambient temperature, package design parameters, and thermophysical properties of the package and PWB materials. A two-tier modeling approach, which accurately accounts for multidimensional heat transfer effects caused by substrate features such as vias and C5 solder joints, has been developed and implemented. In this methodology, the effect of small features is first characterized using a detailed micromodel from which an effective thermal conductivity is computed. The effective thermal conductivity is implemented in the global model thereby excluding the small features in the global model. The actual stackups of the package and PWB have been used in the computations to accurately determine the in-plane heat spreading. Using this methodology for automotive underhood applications, a parametric study of thermal performance of the WB-PBGA package has been carried out. This study shows that: 1. The maximum junction temperature rise above ambient, ΔT, decreases with increase in ambient temperature by 30% as the ambient temperature increases from 23 to 125°C. 2. ΔT decreases by 20% as the emissivity of the molding compound and the PWB surfaces increases from 0 (no radiative loss) to 0.8 under natural convection conditions. 3. The decrease in ΔT is small (∼7%) as the thermal conductivity of the die attach material varies over a wide range. 4. ΔT decreases by 30% as the thermal conductivity of the molding compound is varied over a wide range. 5. ΔT decreases by 45% as the thermal conductivity of the substrate increases (i.e., as the number of vias in the substrate increase) from no vias case to densely populated vias.

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Parametric Studies of the Thermal Performance of a Tape Ball Grid Array (TBGA) Package

10.1115/imece2000-1837 ◽

2000 ◽

Author(s):

Sandeep S. Tonapi ◽

Sanjeev B. Sathe ◽

K. Srihari ◽

Bahgat B. Sammakia

Keyword(s):

Heat Transfer ◽

Thermal Performance ◽

Heat Dissipation ◽

Physical Phenomenon ◽

Ball Grid Array ◽

Cover Plate ◽

Transfer Model ◽

Back Side ◽

Significant Difference ◽

Parametric Studies

Abstract This paper deals with parametric studies to evaluate the thermal performance of a Tape Ball Grid Array (TBGA) package. A cover plate is attached to the back side of the chip to enhance heat transfer from the module. The package is attached to an organic carrier and placed in a vertical channel. A conjugate heat transfer model is used accounting for conduction in the package and the card and convection in the surrounding air. The effect of location of the TBGA on a card with 0, 1 and 2 power planes is evaluated for thermal performance. Five different locations of the TBGA on the card are investigated. Heat dissipation is studied for forced convection (2, 1, and 0.5m/s). No significant difference in chip junction temperatures for the different locations is observed. Temperature distribution along the card centerline and the module centerline are used to discuss the physical phenomenon that is occurring.

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