PC8245 Datasheet, PDF (20/61 Pages) ATMEL Corporation – Integrated Processor Family

Heat Sink Usage
20 PC8245
The board designer can choose between several types of thermal interface. Heat sink
adhesive materials should be selected based upon high conductivity, yet adequate
mechanical strength to meet equipment shock/vibration requirements. There are several
commercially-available thermal interfaces and adhesive materials provided by the fol-
lowing vendors:
Chomerics, Inc.
77 Dragon Ct.
Woburn, MA 01888-4014
Internet: www.chomerics.com
781-935-4850
Dow-Corning Corporation
Dow-Corning Electronic Materials
2200 W. Salzburg Rd.
Midland, MI 48686-0997
Internet: www.dow.com
800-248-2481
Shin-Etsu MicroSi, Inc.
10028 S. 51st St.
Phoenix, AZ 85044
Internet: www.microsi.com
888-642-7674
Thermagon Inc.
4707 Detroit Ave.
Cleveland, OH 44102
Internet: www.thermagon.com
888-246-9050
An estimation of the chip junction temperature, T_J, can be obtained from the equation:
T_J = T_A + (R_θJA x P_D)
where
T_A = ambient temperature for the package (°C)
R_θJA = junction-to-ambient thermal resistance (°C/W)
P_D = power dissipation in the package (W)
The junction-to-ambient thermal resistance is an industry-standard value that provides a
quick and easy estimation of thermal performance. Unfortunately, two values are in
common usage: the value determined on a single layer board and the value obtained on
a board with two planes. For packages such as the TBGA, these values can be different
by a factor of two. Which value is closer to the application depends on the power dissi-
pated by other components on the board. The value obtained on a single layer board is
appropriate for the tightly packed printed-circuit board. The value obtained on the board
with the internal planes is usually appropriate if the board has low power dissipation and
the components are well separated.
When a heat sink is used, the thermal resistance is expressed as the sum of a junction-
to-case thermal resistance and a case-to-ambient thermal resistance:
R_θJA = R_θJC + R_θCA
where
R_θJA = junction-to-ambient thermal resistance (°C/W)
R_θJC = junction-to-case thermal resistance (°C/W)
R_θCA = case-to-ambient thermal resistance (°C/W)
2171D–HIREL–06/04