The early industry standards for heat transfer of power adapters are mainly
SEMI standards, which define the test standards for IC packages in natural
convection, wind tunnel and infinite flat test environments. Today, follow the
editor to understand the packaging heat transfer standard of the power
adapter!
Since 1990, the JEDECJC51 committee has invited manufacturers and experts
to formulate new industrial standards for heat transfer, and put forward a
number of standards for thermal management. Compared with the SEMI standard, the
new heat transfer industry standard has the same basic measurement methods and
principles, but the content is more complete, and some definitions are also more
clearly explained.
The SEMI standard defines two thermal resistance values, namely Rja and
Rjc. Among them, Rja is a measure of heat transfer from the chip interface to
the atmosphere in natural convection or wind tunnel environments. Since the
measurements are made under standard specification conditions, and therefore
have different results for different substrate designs and environmental
conditions, this value can be used to qualitatively compare the ease with which
the package dissipates heat. Rjc refers to the thermal resistance of heat from
the chip interface to the IC package. It needs to be in contact with an
isothermal surface during measurement. This value is mainly used to evaluate the
performance of the heat sink.
With the change of package form, several measurement parameters such as
Rjb, ψjt, ψjb have been added in the new JEDEC standard. Among them, Rjb is the
thermal resistance from the chip interface to the test board in the environment
where almost all the heat is transferred from the chip interface to the test
board. This value can be used to evaluate the heat transfer efficiency of the
PCB. ψjx is a heat transfer characteristic parameter, which is defined as
follows.
(1) The definitions of ψ and R are similar, but the difference is that ψ
refers to the case where most of the heat is transferred, while R refers to the
total heat transfer. When the actual electronic system dissipates heat, the heat
will be transferred from the top and bottom of the package or even around the
package, not necessarily in a single direction, so the definition of ψ is more
in line with the actual system measurement.
(2) ψjt refers to the thermal resistance generated when part of the heat is
transferred from the chip interface to the casing above the package. This value
can be used to predict the chip interface temperature from the outer surface
temperature of the IC package in actual system products.
(3) ψjb is similar to Rjb, which refers to the thermal resistance generated
when part of the heat is transferred from the chip interface to the lower test
board under natural convection and wind tunnel environments, which can be used
to predict the junction temperature from the board temperature.
Although various thermal resistance measurements in the standard can be
applied to temperature prediction of actual system products, there are still
great limitations in practical application. When using the standard Rja, Rjb,
ψjt, ψjb and other measurement parameters to predict the temperature of the
system product, it is necessary to pay attention to the test board size, copper
foil layer and copper content used in the standard test conditions, and also to
pay attention to the natural environment used in the measurement. Differences
between convection and wind tunnel environments and actual systems.
Generally speaking, the thermal resistance or heat transfer parameters
measured by experiments are mainly used to qualitatively compare the heat
dissipation efficiency of IC packaging, that is, no matter which packaging
factory is packaged, as long as it conforms to the standard method, the heat
dissipation can be compared. Knowing the thermal design or heat transfer
conditions of an IC package can be of great help. In addition, experimental
measurements can also be used for verification and simplification of numerical
simulations.
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