Tech Talk

When engineering an electronic assembly, many different factors affect which component a designer implements on a given board. The goal of the designer is to select a component that offers the highest reliability under the set of conditions in which they will operate. The conditions to be considered include environmental and mechanical stress as well as operating temperatures under which the system and its components operate. The thermal resistance term is related to these conditions.

The thermal resistance of an oscillator package is defined as the temperature difference that occurs between the semiconductor element within the package and the package's surface or ambient atmosphere when the device consumes 1 watt [W] of power.

Thermal resistance is an indication of the heat transfer from the semiconductor device through all of the package materials out to the open environment. This parameter is often measured in terms of temperature per unit of power, or degrees Celsius per watt (°C/W).

Power dissipation is the transference of heat generated by the device during normal operation.

Semiconductor IC temperatures are a key characteristic in semiconductor operation and long-term reliability. A circuit designer can use the thermal resistance parameters so as to estimate the junction temperature of the semiconductor device within the oscillator.

There are three common thermal resistance parameters used in determining the heat dissipation capability of a package containing a semiconductor device: θ_JC, θ_JA, and θ_CA. θ_JC is defined as the thermal resistance from the semiconductor junction to the case of the oscillator (junction-to-case). A low value of θ_JC corresponds to better heat conduction. A high value corresponds with poorer heat conduction. θ_JA is defined as the thermal resistance from the semiconductor junction to the ambient air (junction-to-ambient). A third term, not often referenced, is called θ_CA. This term is defined as the thermal resistance between package surface and ambient atmosphere. See the figure below for a mechanical representation of these thermal resistance parameters.

θ_JA is defined by the following formula:

θ_JA = θ_JC + θ_CA= (T_J - T_A) / P_D

Where T_J is the junction temperature of the semiconductor device mounted inside the oscillator (measured in °C), T_A is the ambient temperature outside the oscillator (measured in °C), and P_D is the power dissipation of the oscillator (measured in Watts). Given the above equation, the θ_JA parameter is measured in units of degrees Celsius per Watt (°C/W).

θ_JC is defined by the following formula:

θ_JC = (T_J - T_C) / P_D

Where T_J is the junction temperature of the semiconductor device mounted inside the oscillator (measured in °C), T_C is the external case or package temperature of the oscillator (measured in °C), and P_D is the power dissipation of the oscillator (measured in Watts). Given the above equation, the θ_JC parameter is measured in units of degrees Celsius per Watt (°C/W).

The above formulas can be rearranged to calculate the junction temperature (T_J):

T_J = (θ_JA * P_D) + T_A or T_J = (θ_JC * P_D) + T_C

The above formulas can be rearranged to calculate the power dissipation (P_D):

P_D = (T_J - T_A) / θ_JA or P_D = (T_J - T_C) / θ_JC

The following table lists available θ_JA and θ_JC for some of our oscillator offerings:

Series θJC θJA E13C7 15 42 E15C7 15 42 E13D8 15 42 E15D8 15 42 EB13C3 15 42 EB13C5 14 40 EB13E2 15 42 EB15E2 15 42 EB16E2 15 42 EB51F3 24 62 EB51F4 21 63 EB51F5 21 63 EB52E8 15 42 EB52E9 15 42 EB52F3 24 62 EB52F4 21 63 EB52F5 21 63 EC11 21 63 EC13 21 63 EC25 15 42 EC26 15 42 EC27 15 42 EC28 21 63 EC29 15 42 EC31 21 63 EC32 21 63

Series θJC θJA EC35 14 40 EC36 14 40 EC37 14 40 EC39 14 40 EH11 21 63 EH13 21 63 EH14 31 81 EH15 31 81 EH25 15 42 EH26 15 42 EH35 14 40 EH36 14 40 EL13C7 15 42 EL15C7 15 42 EL13D8 15 42 EL15D8 15 42 EMK11 10 30 EMK12 10 30 EMK13 10 30 EMK21 10 30 EMK22 10 30 EMK23 10 30 EMK31 10 30 EMK32 10 30 EMK33 10 30 EMK41 10 30 EMK42 10 30 EMK43 10 30

Series θJC θJA EP11 21 63 EP13 21 63 EP13E7 15 42 EP14 31 81 EP15 31 81 EP15E7 15 42 EP16E7 15 42 EP25 15 42 EP26 15 42 EP35 14 40 EP36 14 40 EPS13D2 15 42 EPS13D3 14 40 EPS13F2 21 63 EPS13H2 21 63 ES51C1 15 42 ES51C5 14 40 ES51F3 24 62 ES51F4 21 63 ES51F5 21 63 ES52C1 15 42 ES52C5 14 40 ES52E9 15 42 ES52F3 24 62 ES52F4 21 63 ES52F5 21 63 ES52K1 15 42 EV31C3 15 42 EV31C6 15 42 EV32C3 15 42 EV32C6 15 42

The amount of airflow around a package can have a significant impact upon the values of θ_JA. The amount of airflow is typically listed in feet per minute (fpm) or meters per second (mps). The Ecliptek θ_JA parameter for all of its oscillator product families is provided using an airflow rate of 0 fpm (free, uncontrolled air).

The ambient temperature around a package during θ_JA measurement is 25°C+/-1°C.

The θ_JA parameter values presented represent oscillator devices that are mounted on a FR4 glass type PCB with copper traces.

The θ_JA and θ_JC values are determined through the use of empirical data, supplier data, and thermal simulation results. In some cases, the actual temperature rise and/or the actual junction temperature of a semiconductor device is known from testing. At other times, these parameters can be determined from certain factors that are known about the component or from information supplied by the vendor of the component. In cases where limited thermal information is known about a component, a standardized temperature rise for that component type may have been used.

The Ecliptek oscillator specification sheet provides two parameters that can be used to determine the maximum power dissipation. Each Ecliptek oscillator specification sheet lists the maximum input current and the nominal supply voltage. The supply voltage tolerance is also provided. Adding the supply voltage tolerance to the nominal value of the supply voltage, the maximum supply voltage can be considered. Power dissipation can be calculated using the following formula:

P_D = V_DD * I_CC

V_DD is the maximum supply voltage (measured in Volts DC) and I_CC is the maximum input current (Measured in Amps). The resultant power dissipation term is measured in Watts (W). Most Ecliptek oscillators have maximum power dissipations in the range of 10mW to 200mW.

The maximum junction temperature (T_JMAX) is defined as the maximum temperature on the surface of the integrated circuit (IC).

Ecliptek does not specify the maximum junction temperature (T_JMAX) for its oscillator product families. The maximum junction temperature (T_JMAX) can be calculated using the above formulas and the θ_JA and θ_JC values for the respective oscillator product family.

The engineering staff at Ecliptek can provide applications engineering support or customer technical questions.