SN65HVD485E

SLLS612 − JUNE 2004

www.ti.com

11

THERMAL CHARACTERISTICS OF IC PACKAGES

divided by the operating power

Standardized testing includes specification of PCB construction, test chamber volume, sensor locations, and the thermal

installations.

TI uses two test PCBs as defined by JEDEC specifications. The low-k board gives average in-use condition thermal

performance and consists of a single trace layer 25 mm long and 2-oz thick copper. The high-k board gives best case in−use

condition and consists of two 1-oz buried power planes with a single trace layer 25 mm long with 2-oz thick copper. A 4%

to 50% difference in

operating power. It is measured by putting the mounted package up against a copper block cold plate to force heat to flow

from die, through the mold compound into the copper block.

junction temperature as it provides pessimistic numbers if the case temperature is measured in a non-standard system and

junction temperatures are backed out. It can be used with

temperature at the center of the package (closest to the die) when the PCB is clamped in a cold−plate structure.

only defined for the high-k test card.

(especially for BGA’s with thermal balls) and can be used for simple 1-dimensional network analysis of package system

(see figure 18).

Surface Node

qJC Calculated/Measured

Junction

qJB Calculated/Measured

PC Board

qCA Calculated

Ambient Node

Figure 17. Thermal Resistance