Datasheet

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THERMAL CHARACTERISTICS OF IC PACKAGES

SN65HVD10-EP , , SN65HVD11-EP

SN65HVD12-EP

SGLS278E – DECEMBER 2004 – REVISED SEPTEMBER 2007

Junction-to-Ambient Thermal Resistance ( θ

) is defined as the difference in junction temperature to ambient

temperature divided by the operating power.

is not a constant and is a strong function of:

• the PCB design (50% variation)

• altitude (20% variation)

• device power (5% variation)

can be used to compare the thermal performance of packages if the specific test conditions are defined and

used. Standardized testing includes specification of PCB construction, test chamber volume, sensor locations,

and the thermal characteristics of holding fixtures. θ

is often misused when it is used to calculate junction

temperatures for other installations.

Texas Instruments 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 copper trace layer 25 mm long and 2 oz thick. The

high-k board gives best case in-use condition and it consists of two 1 oz buried power planes with a single

copper trace layer 25 mm long and 2 oz thick. A 4% to 50% difference in θ

can be measured between these

two test cards

Junction-to-Case Thermal Resistance ( θ

) is defined as difference in junction temperature to case divided by

the 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.

is a useful thermal characteristic when a heatsink is applied to package. It is not a useful characteristic to

predict junction temperature because it provides pessimistic numbers if the case temperature is measured in a

nonstandard system and junction temperatures are backed out. It can be used with θ

in one-dimensional

thermal simulation of a package system.

Junction-to-Board Thermal Resistance ( θ

) is defined as the difference in the junction temperature and the

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

structure. θ

is defined only for the high-k test card.

provides an overall thermal resistance between the die and the PCB. It includes a bit of the PCB thermal

resistance (especially for BGAs with thermal balls) and can be used for simple one-dimensional network analysis

of the package system (see Figure 24 ).

Figure 24. Thermal Resistance

Product Folder Link(s): SN65HVD10-EP SN65HVD11-EP SN65HVD12-EP