Package Thermal Characterization Effective heat removal from chip

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Package Thermal Characterization Effective heat removal from chip

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Package Thermal Characterization
Package Thermal Characterization
Effective heat removal from chip, through package, adjacent environment crucial maintain allowable device junction temperature. latter directly affects electrical circuit performance both component system levels. Aside from thermal enhancement individual packages manufacturers, proper printed circuit board (PCB) layout cabinet design users also substantially reduce overall package thermal resistance. fundamentals various heat transfer modes found classic heat transfer textbook, recent advances heat transfer fluid flow development referred from published technical papers. Thus, intent this application note threefold: provide practical aspects package thermal resistance definition; show data generated; and, discuss package mounting, board effect, system effect heat transfer. This application note first covers basics package thermal characterization help user interpreting package thermal data. Subsequently, package mounting effects, board effects, system effects package heat transfer outlined, along with some critical dimensions. last section summary major guidelines user obtain better thermal design board system levels. where TC)/P, junction-to-case conductive thermal resistance (°C/W) TA)/P, case-to-ambient convective thermal resistance (°C/W) (Current) (voltage), Device heat dissipation Average device junction temperature (°C) Average ambient temperature (°C) Case temperature prescribed package surface (°C).
dominated conductive thermal resistance within layers packaging materials, highly dependent package configuration. heat flow assumed perpendicular each layer packaging material, expressed
ti/(ki where thickness, thermal conductivity, heat transfer surface area each packaging material layer, e.g., attach material, lead frame, coating, encapsulant. external convective thermal resistance. greatly affected adjacent ambient conditions, package boundary conditions, conjugate heat transfer.
Package Thermal Characterization
Thermal properties electronic packages characterized which widely used electronic industry. defined overall package thermal resistance, which package internal external thermal resistance. expressed TA)/P
Figures Figure describe package thermal experiments, (Temperature Sensitive Parameter) diode calibration procedure, deriving methods, summarized (1). Typically, physically measured high precision thermocouple wires. indirect measurement extracted from diode calibration curve. average device power calculated product measured current flow voltage across power ground pins given package. measured values recorded thermal equilibrium state room temperature atm. conditions. Details measurements procedures found elsewhere (2), together with data generated with thermal test chip (3).
2000 National Semiconductor Corporation
MS011816
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Package Thermal Characterization
Package Thermal Characterization
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FIGURE Package Thermal Experiments
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Package Thermal Characterization
Package Thermal Characterization
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FIGURE Diode Calibration
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FIGURE Deriving Methods
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Package Thermal Characterization
Package Thermal Characterization
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FIGURE Deriving Method Tabular thermal data this databook list typical package thermal resistance data from each package family with different lead counts. data generated with packages mounted National Semiconductor's standard FR-4 test boards, which conform SEMI/JEDEC standards designed certain package families. Typically, overall thermal resistance decreases with increase forced flow rate, when flow becomes fully developed temperature profile does fluctuate. this stage, even with further increases flow rate, overall package thermal resistance stays relatively unaffected. size increases given package, overall package thermal resistance decreases reduction power density. Thermal testing user's board system product made regional Sales representative when your thermal loading condition largely different from standard test conditions. user stringent thermal requirements critical applications, package thermal resistance reduced further with embedded heat spreaders particular lead frame designs. stalling metal rail underneath package, increasing metal trace footprint area enhance heat conduction from ground pins. Care must taken when external heat sink mounted package, since drag generated flow field depending position package board.
Board Effect
printed circuit board acts heat sink providing path(s) individual packages effectively transfer heat board adjacent environment. Thus, maximizing area metal trace where power ground pin(s) package located important effective heat transfer pointed (4). enhance "chimney effect", pressure drop between flow inlet outlet, across entire flow field, should maximized. This achieved reducing friction flow with proper layout packages different heights. Furthermore, high power devices placed near leading edge trailing edge board, that potential thermal runaway longer concern. board should attached closer cold plate wherever possible. board should never placed with mounted packages facing down same direction gravitational force, that convective currents available. board facing higher power devices positioned board center, case locations along board edges occupied. rule thumb, packages upper levels always preheated packages lower positions. This preheating effect considered board level thermal analysis.
Package Mounting (Through Hole Surface Mount)
Package pin-to-board solder joints should free voids minimize unwanted thermal resistances. Depending package style, there inherent thermal limitation each package family. instance, DIPs mounted board typically have wider from board-to-package bottom than SOs. This differential results poor package thermal performance. Nevertheless, improvement obtained providing additional heat path board such inwww.national.com
Package Thermal Characterization
System Effect
Cabinet height-to-width/depth aspect ratio board-to-board spacing, adjacent package spacing have significant effects overall system thermal performance. addition ergonomics, typical cabinet aspect ratio close Certain large protruding packages from board induce drag flow, where desired channel cabinet pressure drop altered. When radiant heat transfer longer negligible, polished aluminum cabinet interior close mirror image promote system heat transfer. Thus, basic understanding natural, forced, mixed convection, combined conduction, convection, radiation, fluid flow would useful facilitation overall thermal design. Regular cleaning precipitated dust contaminant package board surfaces maintain thermal stability system.
Place high power devices near leading edge trailing edge board when board oriented vertically. other hand, when board oriented horizontally, position high power devices face within center,
Mounting heat sink package should also take into consideration heat transfer effect adjacent packages, Strengthen radiant heat with increase surface emissivity. overall thermal resistance package reduced significantly addressing comprehensive thermal management from component level, board level, system level.
References
Lin, "Thermal Characterization Semiconductor Packages", Nordic Cooling Electronics Conference, Gothenberg, Sweden, November 18-19 (1992). Mindock, "Thermal Resistances Joint Army Navy (JAN) Certified Microcircuit Packages", RADC-TR-86-97, Rome Development Center, Force Systems Command, Griffiss AFB, (1986). Pendse Shanker, Study Thermal Performance Packages Using Test Die", IEEE Semiconductor Thermal Temperature Measurement Symp., 50-54 (1988). Simpson, "The Fundamental Thermal Design", Electronic Design, 95-100, September (1991).
Summary
thermal resistance approach electrical analogy, far, simplest method analyzing thermal behavior from component level system level. following practical thermal guidelines useful providing component system reliability, which meet best interests both semiconductor manufacturers users: Provide sufficient conduction paths from package board adapt direct heat sink approach, Enhance convective heat transfer board along board cabinet diverting flow simulate impingement spot regions,
National does assume responsibility circuitry described, circuit patent licenses implied National reserves right time without notice change said circuitry specifications.

Package Thermal Characterization Effective heat removal from chip

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