Device Mounting Procedures Power Dissipation George Krausse Phone

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Application Note 1810 October 2009
Device Mounting Procedures Power Dissipation
George Krausse Phone: 541-382-8028 ext. 1200 gkrausse@microsemi.com Dick Frey Phone 541-382-8028 ext. 1111 dfrey@microsemi.com Choi Phone: 541-382-8028 ext. 1205 gchoi@microsemi.com
Introduction: values power dissipation semiconductor device derived from values thermal resistance. Therefore, package design mounting that defines power dissipation capability device. this section present elements necessary arrive engineering values RJHS define their relationship PDC, PDHS. doing illustrate process these specifications. Definitions: clarity accuracy, essential that operate with same understanding definitions terms used. Given: defined thermal resistance from junction case (C), with case held 25°C junction limited MAX. RJHS defined thermal resistance from junction heat sink (HS), with heat sink held 25°C Junction limited MAX. defined maximum power dissipation capability device with junction limited MAX, case held 25°C. PDHS defined maximum power dissipation capability device with junction limited MAX, heat sink held 25°C. Then:
TCASE
PDHS
THEATSINK
These definitions based repeating limits, heat sink case held 25°C. This logical approach with clearly defined limits they international standard, however they represent real world values. cooling system that would maintain case heat sink 25°C, power levels necessary, possible would practical vast majority commercial applications. Therefore, realistic user heat sink temperatures should used calculations power junction temperature. most applications heat sink temperature will typically 40°C 55°C.
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Application Note 1810 October 2009
Mounting instructions Flangeless Packages
Introduction: correct mounting power device heat-sink most important step obtaining manufacturer's published specifications. average, approximately half RJHS thermal resistance thermal compound layer which between bottom substrate heat sink. Chart illustrates Temperature each materials vertical stack devices; however directly applicable power devices. Blue column Chart total available device. column contribution thermal compound, which more than half total. conventional, devices heat sink designs face this problem. fact that proper device heat sink mounting paramount concern overstated. Chart illustrates Temperature profile (DRF1400) from surface heat sink surface. This further illustrates critical nature thermal compound layer. temperature rise from heat sink, 25°C, surface, 175°C, 150°C. temperature rise thermal compound 118°C, total available temperature rise. Chart
MATERIAL DELTA
Chart
Surface
Solder Layer First Metal Layer Substrate Layer Second Metal Layer Zero this model
Thermal Compound Layer
Heat Sink Surface
SOLDER METAL SUBSTRATE METAL THERMAL COMPOUND TOTAL
DRF1400
should noted that thermal compound shown Chart typical value Material, Application, Seating Torque. assumed thickness 0.001in, compound AVVID, Thermalloy. Ther-o-Link, 1002. These topics addressed more detail following sections.
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Application Note 1810 October 2009
Device Preparation: following section presents recommended heat-sink mounting procedures devices Flangeless Package family. Figure shows arrangements. arrangement left spaced heat sink. arrangement right mounted flat against heat sink.
Figure Lead Bending Prior Seating First, bend leads upward away from direction lid, about angle, illustrated Figure This prevents damage leads during following processes. bottom surface device must free foreign objects material. Material: Heat Sink Surface: heat sink surface must smooth, clean free nicks burs. must flat, mil/in, finished 50µin.
Failure follow guidelines above have significant impact device performance point damaging device during mounting process later during device operation. bottom surface must coated with uniformly thin film thermal compound. best performance, 0.001in. thick suggested. this process either device heat sink coated with thermal compound. Preferred Method Thermal Compound Application: preferred method thermal compound application, production environment, apply compound using screen printer. This process insures consistent repeatable performance.
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Application Note 1810 October 2009
Application Thermal Compound Heat Sink Hand: thermal compound applied heat sink device, both. Figures thru illustrate compound being applied heat sink.
roller coated with very thin layer thermal compound. roller available from: Speed Ball Products Product #4170
Figure Uniform Coating Thermal Compound Roller
First, apply compound heat sink direction parallel heat sink fins. This done three complete strokes direction.
Figure Roll Left Right Times
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Application Note 1810 October 2009
Next, apply additional thermal compound angle first coat compound, again three strokes roller direction.
Figure Roll Down Times Figures thru illustrate Thermal compound being applied Device.
device clean free foreign matter ready application thermal grease.
Figure Device Ready Apply Thermal Grease
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Application Note 1810 October 2009
Apply grease along length device three strokes direction.
Figure Apply Grease along Length Device
Apply grease along width device three strokes direction.
Figure Apply Grease along Width Device
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Application Note 1810 October 2009
device ready mount.
Figure Device Ready Mount Seating Device: this point attachment process, from either thermal compound application heat sink thermal compound application device, seating step required.
Movement Pressure Points
.200in. Microsemi DRF1300
Movement
Movement
.200in.
Movement
Figure Seating Device illustrated Figure place device heat sink seat using small downward pressure sideto-side motion, followed front back motion remove trapped excess thermal compound. www.microsemi.com 7/11
Application Note 1810 October 2009
Note small Grain pattern, This near Ideal.
Figure Uniform Coating Thermal Grease Figure same device after proper seating. purpose side-to-side motion spread grease evenly, express much excess compound possible from interface, eliminate pockets. Heat sink cleanliness surface preparation very important. Common Problems: Common problems with device mounting heat sink surface finish illustrated Figure
Small Grain Pattern Preferred
Void Caused Warped Heat Sink Scratches permitted
Small Grain Patterns left illustrate proper thickness thermal compound. This large void most often caused contamination, instead warped heat sink. Scratches like illustrated Figure cause void thermal compound very area, area under power devices.
Figure Poor Heat Sink Surface Figure above, preferred small grain pattern upper right. This fine pattern indicator thermal compound thickness, illustrated Figure
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Application Note 1810 October 2009
Figure Bottom View Source lead (VRF154 shown) some Flangeless Package family (VRF154 157), source terminal bottom device shown Figure source leads directly captured four mounting screws there internal bridge between two. device designed compress source lead against heat sink, which typical large devices this class with base plate. electrical resistance this configuration equivalent device with base plate difference gain, base plate base plate, indistinguishable.
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Application Note 1810 October 2009
Mechanical Attachment: plastic/fiber-glass package designed have mechanical compliance. This evens balances pressure applied substrate prevents cracking substrate. package guaranteed flat parallel lower surface BeO. Therefore, flat placed package apply compressive force recommended. flat placed package used apply compressive force, compliant between required prevent cracking substrate.
Figure Side View package. four screws (1-2-3-4), shown Figure should installed seated. Then torque one-half specification, sequence shown. First screw then finally Complete process tightening full specification same manner. Torque specification 8in.lb.
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Application Note 1810 October 2009
Lead Attachment: common lead bending approaches bend bend. leads should prepared with bend, shown Figure Drain lead bend shown Gate lead. type location bend used dependant user's topology, recall Figure
Figure Stress Relief Bend, (VRF154 shown) leads should soldered after mounting device. Lead temperature must exceed 300°C 10s.
Heat Sink Mounting References: Thermal Compound, AVVID, Thermalloy. Ther-o-Link, 1002. recommended Devices. Keratherm-Thermal Grease, KP97, KP12 Note pressure graph. International Rectifier Application note AN-997, Mounting Guidelines Super-247. Motorola Application Note, Mounting Considerations Power Semiconductors AN1040.
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Rev. 11/06/09
11/11

Device Mounting Procedures Power Dissipation George Krausse Phone

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