PowerPC 740 and PowerPC 750 Microprocessor Datasheet - IBM

More documents

Recommendations

Info

PowerPC 740 and PowerPC 750 MicroprocessorCMOS 0.20 µm Copper Technology, PID-8p, PPC740L and PPC750L, dd3.2Internal Package Conduction ResistanceFor the exposed-die packaging technology, shown in ”Package Thermal Characteristics1,” on page 11, theintrinsic conduction thermal resistance paths are as follows.• Die junction-to-case thermal resistance• Die junction-to-ball thermal resistanceFigure 22 depicts the primary heat transfer path for a package with an attached heat sink mounted to aprinted-circuit board.Figure 22. C4 Package with Heat Sink Mounted to a Printed-Circuit BoardExternal ResistanceRadiationConvectionInternal ResistanceHeat SinkPrinted-Circuit BoardThermal Interface MaterialDie/PackageChip JunctionPackage/LeadsExternal ResistanceRadiationConvection(Note the internal versus external package resistance.)Heat generated on the active side (ball) of the chip is conducted through the silicon, then through the heatsink attach material (or thermal interface material), and finally to the heat sink; where it is removed by forcedairconvection. Since the silicon thermal resistance is quite small, for a first-order analysis, the temperaturedrop in the silicon may be neglected. Thus, the heat sink attach material and the heat sink conduction/convectivethermal resistances are the dominant terms.Adhesives and Thermal Interface MaterialsA thermal interface material is recommended at the package lid-to-heat sink interface to minimize the thermalcontact resistance. For those applications where the heat sink is attached by a spring clip mechanism,Figure 23 shows the thermal performance of three thin-sheet thermal-interface materials (silicon, graphite/oil,flouroether oil), a bare joint, and a joint with thermal grease, as a function of contact pressure. As shown, theperformance of these thermal interface materials improves with increasing contact pressure. The use of thermalgrease significantly reduces the interface thermal resistance. That is, the bare joint results in a thermal9/6/2002 Version 2.0 Page 46
PowerPC 740 and PowerPC 750 MicroprocessorCMOS 0.20 µm Copper Technology, PID-8p, PPC740L and PPC750L, dd3.2resistance approximately 7 times greater than the thermal grease joint.Heat sinks are attached to the package by means of a spring clip to holes in the printed-circuit board (seeFigure 21). Therefore the synthetic grease offers the best thermal performance, considering the low interfacepressure. Of course, the selection of any thermal interface material depends on many factors—thermal performancerequirements, manufacturability, service temperature, dielectric properties, cost, etc.Figure 23. Thermal Performance of Select Thermal Interface Material+Silicone Sheet (0.006 inch)Bare JointFloroether Oil Sheet (0.007 inch)Graphite/Oil Sheet (0.005 inch)Synthetic Grease2+Specific Thermal Resistance (Kin 2 /W)1.510.5++0010 20 30 40 50 60 70 80Contact Pressure (PSI)Heat sink adhesive materials should be selected based upon high conductivity, yet adequate mechanicalstrength to meet equipment shock/vibration requirements.The following section provides a heat sink selection example using one of the commercially available heatsinks.Page 47 Version 2.0 9/6/2002
Page 1 and 2: PowerPC 740 and PowerPC 750Micropro
Page 5 and 6: PowerPC 740 and PowerPC 750 Micropr
Page 45: PowerPC 740 and PowerPC 750 Micropr

PowerPC 740 and PowerPC 750 Microprocessor Datasheet - IBM

Create successful ePaper yourself

Delete template?

Save as template?