Thermal resistance junction-to-case

The flow of heat from the junction of a semiconductor device through the device material and on through several layers of an interconnect substrate may be treated as a series of temperature drops or thermal resistances at each interface. The junction-to-case thermal resistance jc expressed in °CAV is widely used in thermal analysis. The junction-to-case thermal resistance is proportional to the drop in temperature from the semiconductor junction to the case and inversely proportional to the power dissipation, thus ... 

The control of bond line thickness is essential for high-power devices. A thin bond line is required since thickness is directly proportional to the junction-to-case thermal resistance, jc (see Chapter 2). Specially formulated solvent-based hybrid adhesives... 

Bondline thickness. The control of bondline thickness is essential for high-power devices. A thin bondline is required since thickness is directly proportional to the junction-to-case thermal resistance, Qjq (see Ch. 2). Specially formulated solvent-based hybrid adhesives can produce uniform bondline thicknesses of one mil or less. Small hard spacers, acting as shims, added to paste adhesive formulations, have also been used to control thickness.The use ofpreforms instead of paste adhesives also assures reproducible thicknesses provided uniform pressure and temperature are applied during curing. 

The sensitive electronic circuitry of a power transistor at the junction is protested by its case, which is a rigid metal enclosure. Heat transfer characteristics of a power transistor are usually specified by the manufacturer in terms of the case-to-ambient thermal resistance, which accounts for both Ihe natural convection and radiation heat transfers. 

The device data sheets provide information regarding the following parameters case options, see Fig. 10.35 for case types maximum operating junction temperature T/(niax) (°C) thermal resistance junction to ambient (no heat sink) 9ja, and thermal resistance junction to case 9jc-... 

A custom CMOS integrated circuit measuring 0.35 x 0.35 x 0.022 in. is mounted in a 1-in. square ceramic quad flat package (QFP). The device dissipates 10 W during normal operation. Find the thermal resistance from junction to case. 

The total thermal resistance from junction to case bottom is the sum of the three individual thermal resistances. 

CNT junctions and agglomerates, or via the matrix. In all these cases, the transition occurs via an interface, and, thus, the coupling losses can be attributed to an intense phonon boundary scattering. At the same time the thermal conductivity decreases with the increase in temperature (if the temperature is near the melting point of the matrix). This indicates that the thermal conductivity of the composites is dominated by the interface thermal transport between the nanotube/matrix or nanotube/nanotube interface. Thus, it is believed that the decreased effective thermal conductivity of the studied composites could be due to the high interface thermal resistance across the nanotube/matrix or nanotube/nanotube interfaces. 

Thermal resistance for junction case Ojc and thermal resistance for junction to ambient, 0jj. (This assumes no heat sink is used). These two values are important for determining heat-sink requirements. 

Note that in the literature, the total thermal resistance 0, usually under natural convection cooling conditions, is also referred to as 9j-a (junction-ambient), 6>int as 9j-c Ounction-case), and 9 xt as 9c-a (case-ambient). 

Boron Thermopiles. The boron thermopiles are used for an additional check on neutron flux level. They are located, in the graphite. (VG-27, 28, 42, 44, 56 see Fig.- 3.F) all at the same horizontal level. These instruments consist of a large number of thermocouple junctions in series, with alternate junctions coated with boron. The coated junctions become warm owing to absorption of neutrons, thus yielding a net voltage which is a measure of neutron flux. The instrument case is about H in. in diameter by 6 in. long. The approximate sensitivity is 6 mv in a flux of 10. Internal resistance is of the order of 3 to 4 ohms. By proper mounting and thermal insulation of the thermocouples the instruments may be made quite insensitive to ambient temperature (say, 40 /xv/°C). For transient conditions the time constant is about 1 sec. 

The resistance to phonon movement from one nanotube to another through the junction will hinder phonon movement and, hence, limit the thermal conductivity. The low thermal conductivity could be partly due to the non-uniform diameter and size, as well as the defects in and the nanoscale dimension of MWCNTs. However, the numerous junctions between carbon nanotubes involved in forming a conductive path and the exceptionally low thermal conductance at the interface, are believed to be the main reason for the low thermal conductivity. The effect of reducing the thermal conductivity is the transfer of phonons from nanotube to nanotube. This transition occurs by direct coupling between CNTs, in the case of the improper impregnated ropes,... 

---