How to measure device thermal resistance?

In aging tests, we often calculate the junction temperature based on the thermal resistance of the chip, the set furnace temperature, and the measured power consumption, and control the junction temperature within a safe range by adjusting the furnace temperature. The main test methods for package thermal resistance are infrared scanning, electrical measurement, transient thermal test interface method, and can also be obtained through simulation modeling. Infrared scanning is a direct test method, but it requires opening the chip cover and is destructive. The next two sections will discuss the measurement of thermal resistance based on two non-destructive tests: electrical measurement method and transient thermal test interface method.

Thermal resistance usually refers to the resistance encountered when heat flows through a thermal conductor (the temperature difference generated on the thermal conductor).

The common parameters defined by JEDEC are as follows:

According to JESD51-1, the thermal resistance of a semiconductor device from junction to a reference point is:

: Semiconductor junction temperature

: Reference point temperature

: Thermal power consumption of semiconductors

Different thermal resistances can be defined by selecting different reference points according to actual needs.

Test methods and steps of measurement system

1) TSP determination. Generally, BJT selects base-emitter voltage   , MOSFET selects source-drain voltage   , IGBT selects collector-emitter voltage   or gate-emitter voltage   , and diode selects forward voltage drop   as TSP.

2) Obtain the K coefficient. Measure the relationship between TSP and temperature to obtain the K coefficient. Taking the diode as an example, TSP is   , place the device in a constant temperature environment, apply a test current to the device under test   , change the measurement temperature, and after the temperature stabilizes, measure the corresponding   , and establish   the corresponding relationship with the temperature.

 &   : High and low temperatures

 &   = higher and lower   voltage

3) Measure junction temperature

There are two ways to test junction temperature electrically: static test and dynamic test.

Static test:

Based on T3Ster's real-time acquisition, the test method complies with JESD51-1, JESD51-14 and IEC 60747 standards. Static testing is suitable for thermal testing chips.

a. Apply a heating current of magnitude to the device under test   for a duration of   . When the device reaches thermal stability in the working state, remove the heating power and quickly switch the working current to the measurement current.

b. During the process of junction temperature drop, the junction voltage is sampled in real time, and then the junction temperature change over time is obtained through the K coefficient   . The thermal resistance is calculated based on the temperature and power consumption change values.

Dynamic Testing:

Dynamic testing is applicable to most integrated circuit devices. The test mainly includes three steps:

First,   the test current is applied  at the time  , then measured   and converted to the initial temperature using the K factor  .

Second, during   the period, a heating current is applied   and measured   .

Third, turn off the power supply, apply the measurement current again   , and measure   . The junction temperature change is   calculated by multiplying the difference between   and  by the K value. Adding them together  gives the first temperature point   .

In the figure above, the switch is placed on the left for the heating process, and the switch is placed on the right for the test process. Apply the same   heating current for different durations ( )   , and repeat the above steps to obtain the next data T2. Repeat continuously to establish a relationship diagram between junction temperature Ti and time. When Ti no longer changes, the junction temperature reaches a steady state. The corresponding thermal resistance calculated at this time is the steady-state thermal resistance, and the thermal resistance calculated at each time point before steady state is the transient thermal resistance.