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Mailing Address: 11400 Tucson, 85734 Street Address: 6730 Tucson Blvd. Tucson, 85706 Tel: (602) 746-1111 Twx: 910-952-111 Telex: 066-6491 (602) 889-1510 Immediate Product Info: (800) 548-6132
MOUNTING CONSIDERATIONS TO-3 PACKAGES
Hubert Biagi (602) 746-7422 Proper mounting TO-3 packages required assure rated performance reliability. Although procedures simple, ignoring them result poor performance catastrophic failure device. PACKAGE HANDLING TO-3 package rugged hermetic package, damaged with improper handling. Excessive bending twisting package pins crack glass seal around result loss hermeticity. straightening required, clamp against package base using needlenose pliers. This will strain-relieve during straightening operation. Another potential problem cracking internal circuit substrate from bending package base. This caused mounting package onto non-flat surface, improper compressible thermal pad, over-tightening mounting fasteners. TO-3 SOCKET Burr-Brown 0804MC TO-3 socket designed meet requirements high current, high power products such OPA512, OPA541, OPA2541. socket rugged contact design which assures positive reliable contact even when using thermal grease pre-tinned pins. closed-ended contacts will accept full length TO-3 guard against solder flux contamination. socket body center hole which allows direct measurement TO-3 case temperature. FASTENERS fastener hardware used mount TO-3 package very important. Table describes proper hardware combination. Sources fastener hardware listed this bulletin. preferred fastener material stainless steel. Plated steel good alternative. Brass plastic fasteners recommended. mounting holes TO-3 package designed accept 6-32 machine screws; other size should used (see exploded views Figure 1B). pan-head best head style. profile large bearing face properly cover mounting hole, large ride onto welded cover. order maintain proper mounting pressure, Belleville spring washer (also known conical compression washer), recommended. Split ring star lock washers recommended. They typically bottom less than pounds, whereas 150-300 pounds pressure needed
TO-3 Package
6-32 Head
Mounting Joint Teflon Sleeves 0.250" Heat Sink 0804MC Socket Belleville Washer Washers 5/16 Full 5/16 Locknut
FIGURE High Power Application Using 0804MC Socket.
1992 Burr-Brown Corporation
AB-037
Printed U.S.A. March, 1992
SBOA020
6-32 Head
TO-3 Package
Mounting Joint
Heat Sink
Sync Nut
Printed Circuit Board
FIGURE Power Application Using Printed Circuit Board. achieve thermal resistance(1). Belleville washer does bottom therefore absorb thermal expansion package(2) slight compression socket material that occur over time. excellent variation conical washer called Sync Nutand available from EG&G Wakefield. includes spring washer part nut. Belleville washer should installed board heat sink side fastener, package flange. Install large face Belleville washer toward mounting surface. When tightening against board 0804MC socket, install additional No.6N (narrow) flat washer against relatively soft material insure that Belleville washer functions correctly. Tighten fasteners slowly, alternate between them until both tighten specification. recommended tightening torque inch-lbs., with acceptable range inch-lbs. 0.45 0.79 Avoid contaminating fastener threads with thermal grease since change torque readings. Over-tightening fasteners damage package internal substrate, undertightening lead poor thermal performance. Re-torquing required after environmental screening operations such burn-in. permanent installation, all-metal locknut preferred. Don't locknuts with plastic inserts. TO-3 HOLE PATTERN good mounting joint between TO-3 package heat sink requires properly machined mounting hole pattern. Never drill single (large diameter) clearance hole package pins. Drill individual holes each pin. Follow TO-3 hole pattern illustrated Figure best thermal performance, minimum hole size 0.073 inch (#49 drill). Smaller holes could interfere with glass seal around each pin.
RECOMMENDED Brass, Plastic Binding, Flat, Oval, Truss, Fillister, Socket, Washer
BEST Material Fastener Head Stainless Steel
ACCEPTABLE Plated Steel Round,
Washers
No.6 Belleville(1) No.6N Flat 5/16" Full, Sync Nut5/16" Locknut(2)
No.6N Flat
1/4" Threaded, 1/4" Full Split Ring(3) Star Washer
Locking Device
NOTES: Recommended No.6 Belleville washer available from ASMCO (part number 24087; diameter 0.312"; rated 78lbs initial force). high power metal type, elastic inserts recommended. recommended high power temp cycling conditions.
TABLE 6-32 Fastener Hardware. avoid shorting pins heat sink, Teflon tubing sleeve pins. Make sure sleeve length slightly less than thickness heat sink. Most pre-drilled heat sinks larger 3/32 (0.094") holes pins, sleeving required long socket board pattern used. still want sleeve least opposite pins help center package. When wiring directly pins, pins should sleeved, regardless hole size used. word caution concerning anodized heat sinks. Unless know what type anodizing used, trust anodizing provide electrical insulation. Refer section called "Heat Sink Surface Treatment" more information. MOUNTING SURFACE PREPARATIONS general, heat sink mounting area should have flatness finish comparable that TO-3 package. When
Mounting Hole .246 .216 .161 .085
Hole
.235 .125
Thermocouple Hole (Optional)
.043 1.186 .191 .593 .500 Diameter
HOLE TYPE Mounting Thermocouple
NUMBER REQUIRED Optional
HOLE SIZE .147" .073 .067 .157" .094 .070
RECOMMENDED DRILL SIZE
FIGURE TO-3 Hole Pattern. using thinner, power heat sinks, sufficient that mounting area appears flat against straight edge. When mounting thicker material, surface flatness important only thermal performance, avoid distorting stressing package base when tightened down. HEAT SINK SURFACE FLATNESS FINISH JEDEC recommends surface flatness 0.004 inch/inch max. standard flatness tolerance most extruded heat sinks 0.004 inch/inch, maximum, which results typical values closer 0.002 inch/inch. Surface finish normally specified around micro-inches (rms). Testing shown that this acceptable most high power applications(3). good practice polish mounting area with steel wool, followed acetone alcohol rinse, immediately prior assembly. best thermal performance, mounting area heat sink spot faced. This removes oxidation anodization improves surface flatness finish. When using thermal pads instead thermal grease, surface flatness 0.001 inch/inch recommended. When mounting TO-3 package panels, brackets, other structural members system, spot facing required insure proper flatness finish. HEAT SINK SURFACE TREATMENT typical surface treatment aluminum heat sinks black anodized(4) MIL-A-8625, Type This surface treatment prevents corrosion maximizes thermal performance. trust this surface treatment provide electrical insulation. electrical insulation, always specify hard anodized, 0.001 inch thick, MIL-A-8625, Type III. This file hard surface treatment resists scratches punctures, typically rated 200VDC electrical insulation 0.001 inch thick treatment. HEAT SINK THRU-HOLES wary heat sinks with punched, rather than drilled, thruholes. properly done, area around each punched hole depressed into crater with raised mound opposite side. This irregular surface significantly degrade thermal performance. high power, extruded heat sinks, general practice drill hole pattern. holes should de-burred. holes TO-3 pins should chamfered deeply, this will reduce contact area mounting joint. Unless special precautions taken, threading TO-3 mounting holes recommended. threading process also leave raised mound around each hole. Threading mount-
holes also eliminates possibility using Belleville washers locknuts proper control mounting pressure. MOUNTING THERMAL RESISTANCE Even proper mounting preparations followed, thermal resistance mounting joint will consist largely small gaps. Only small percentage mounting area will actually have metal-to-metal contact. minimize thermal resistance, these gaps must filled with stable, thermally conductive material. Table describes common thermal fillers available performance that expected. Note that tightening torque mounting fasteners also affects thermal performance(5).
HEAT SINK FLATNESS REQUIREMENTS Very sensitive variations flatness finish sensitive, standard .004 inch/inch (max) lowest .001inch/inch (typ) recommended lowest .001inch/inch (typ) recommended lowest .001inch/inch (typ) recommended Text recommended Mica brittle prone crack
BARE MOUNTING no-load power applications, mount TO-3 package bare against heat sink. high power applications, this recommended, even extra thermal resistance acceptable. This because thermal resistance bare joint vary greatly depending surface flatness finish heat sink. THERMAL GREASE lowest thermal grease should used conjunction with properly machined finished mounting surface. This combination will result about 0.1°C/W. Using proper fastener hardware critical maintaining this thermal resistance over time temperature. There many suppliers thermal grease (also known heat sink compound). Thermal grease formulation fine zinc oxide other thermally conductive, electrically insulating, particles silicone other synthetic based fluid. shelf life most thermal greases indefinite when kept sealed container, over time, separate out. Mixing components back together before will restore thermal properties. Thermal grease should applied excess, objective fill gaps, decrease amount metal-tometal contact. Slight rotation TO-3 package against heat sink will promote even spreading. With correct amount applied fasteners properly torqued, very small bead thermal grease should appear around perimeter TO-3 package. Although grease over time, this does degrade thermal resistance provided mounting joint remains tight.
DESCRIPTION Bare Joint
(°C/W)
APPLICATION power only
Thermal Grease
High Power
Aluminum Foil(1) (pre-coated with alumina filled silicone) Aluminum Foil(2) (pre-coated with thermal grease) Kapton(3) (pre-coated with thermal grease) Silicon Rubber (compressible) Mica (bare) Mica (with thermal grease)
High Power
High Power
Electrical Insulation Electrical Insulation Electrical Insulation
where (Watts) Case Mounting Resistance Heat Sink Ambient
NOTE: Available from BERGQUIST, part number QII-88 (with .094 inch holes). Available from Power Devices, part number AL-155-10C. Available from Crayotherm, part number TO-3-8 CR2-MT. Appendix manufacturers listings.
Power Dissipated
Junction
Range Thermal Resistance Values (°C/W)
TABLE Thermal Interface Options TO-3 Packages. Understanding thermal model system will enable make best mounting compromises. Consider simplified thermal model Figure mounting thermal resistance represented (case-to-heat sink). overall thermal resistance represented (junction-to-ambient). power applications, high 30°C/W. this case, mounting thermal resistance significant portion overall thermal resistance. high power applications, 1°C/W. Then critical obtain example, power dissipation 50W, additional 0.5°C/W mounting thermal resistance will increase junction temperature 25°C.
FIGURE Simplified Thermal Model.
THERMAL PADS Thermally conductive pads offer cleaner, simpler method improving thermal interface. lowest attainable using thermal about 0.2°C/W, which almost good thermal grease. However, should approach with caution multitude different materials, designs, applications thermal pads. Basically there types thermal pads, electrically insulating electrically conductive. Electrically insulating pads designed used with discrete transistor TO-3s, which have electrically isolated package. general, they provide enough high power because dielectric layer must sandwiched into pad. Hybrid TO-3s with isolated headers require electrically isolated pads. They electrically conductive pads. Without need dielectric layer, very achieved, almost good thermal grease. While they good filling small gaps, thermal pads suffer same problem when used against heat sinks with standard flatness tolerances 0.004 inch/inch. They flow conform with surfaces does thermal grease. Therefore, recommended that whenever thermal pads used, mounting area should spot faced typical surface flatness 0.001 inch/inch. Silicon rubber pads also sensitive surface flatness(6). Approach these with caution. Most improve thermal performance over bare joint. compressibility these rubber pads cause package header flex possibly crack internal substrate. They also settle over time temperature, resulting loose fasteners mounting pressure. SUGGESTED MOUNTING SCHEMES mounting schemes presented here address more common operating conditions TO-3 power products (see Figure These conditions include high power operation, power operation, functional testing under unloaded, quiescent conditions. options 0804MC socket, individual cage jacks, direct board soldering. Table describes recommended cage jacks.
FUNCTIONAL TESTING NO-LOAD CHARACTERIZATION functional testing no-load characterization room temperature, heat sinking required. These mounting schemes least critical easiest fabricate. When using 0804MC socket, socket mounted directly test board drilling single clearance hole eight socket contacts. hole should (0.63 0.75) inches diameter. careful short copper cladding metal contacts. socket body should mounted using flat head machine screws. electrical insulation, nylon flat head machine screws used instead. When using cage jacks, follow TO-3 hole pattern illustrated Figure close ended cage jacks whenever possible avoid solder contamination. POWER OPERATION mounting schemes power applications extension those used functional testing no-load characterization. difference that small heat sink must attached TO-3 package. overall thermal resistance (JA) power applications relatively high, from 30°C/W. Therefore, critical high power operation. most instances, TO-3 package mounted bare. power heat sinks usually stamped rather than extruded, some even press around TO-3 cover. They called "low power" "standard" heat sinks versus "high power" "extruded" heat sinks used high power operation thermal resistance these types heat sink range from °C/W, depending their size, weight, design. power mounting schemes commonly used board applications. these applications, heat sink manufacturers have developed many custom accessories such wave solderable fasteners thermally conductive pads. These must approached with caution. important follow specific recommendations this bulletin. Thermal pads discussed section called "Thermal Mounting Resistance". recommended fastener board applications Sync NutTM. This fastener allows TO-3/heat sink combination wave soldered directly board. Re-torquing should performed after wave solder. power applications that involve temperature cycling, split ring lock washers safely used. HIGH POWER OPERATION Mounting schemes high power operation involve larger, heavier heat sinks, that machined rather than stamped. Their size weight usually requires that they integrated into system layout, rather than simply attached TO-3 package. general, they length from extruded sections, thus often called "extruded" heat sinks.
MANUFACTURER Cambion
PART NUMBER 450-3716-01-03
DRILL SIZE INCHES (NUM) .076
COMMENTS Knock-out bottom permits wave soldering. Heavy duty, open ended. board press fit. Closed end, accepts full length.
Concord Technology Mil-Max
09-9047-1-03 MC76 0325-0-1501-34-27-10-0
.104 .089 .089
(See Appendix manufacturers listings)
TABLE III. Recommended Cage Jacks.
Board
Metal Board Clearance Hole Socket Contacts
Split Ring Lockwasher
Cage Jacks: Cambion 450-3716-01-03 (For complete listing Table III).
No-Load Applications: (CA: 30°C/W)
Threaded
Heat Sink
0804MC Socket
6-32 Head
Metal Board
Nylon Fasteners Socket
Soldered Pins
Sync Nut
Low-Power Applications: (HA: 3-20°C/W)
Heat Sink Thickness 0.250 Inches
Teflon Sleeves
6-32 Head Heat Sink
Teflon Sleeves
Belleville Washer Locknut 0804MC Socket Board Cage Jacks: Cambion 450-3716-01-03 (For complete listing Table III).
High-Power Applications: 125W (HA: 0.4-3°C/W)
FIGURE TO-3 Mounting Examples.
thermal resistance these types heat sink range from 3°C/W operation still air. With forced air, reduced one-half two-thirds. high power applications, overall thermal resistance (JA) 1°C/W. Under these conditions, obtaining critical. insure good mounting joint, recommended fastener hardware surface preparations described previous sections this application bulletin. THERMAL MEASUREMENT EVALUATION always good idea check TO-3 mounting scheme measuring package case temperature (TC) under actual operating conditions. semiconductor junction temperature (TJ) then calculated from case temperature, indicated Figure where total power dissipation (including quiescent power) junction-to-case thermal resistance (given product data sheet). calculated junction temperature should less than maximum allowable temperature indicated product data sheet (typically 150°C). true case temperature located directly below substrate centered within package pins (see Figure This location, called case backside, will also give most repeatable measurements. directly access case backside, drill heat sink with optional thermocouple hole(7) illustrated Figure recommended thermocouple
Omega fast-response probe (part SDX-SET-RT-KSMP). Allow enough time system reached thermal equilibrium. touch thermal grease probe will ensure good thermal contact. package case temperature also estimated fitting spade-lug type thermocouple under head mounting fastener. This will give temperature mounting flange package rather than case backside. case backside will actually hotter than mounting flange. difference large 10°C, depending power dissipation, mounting thermal resistance, etc. high power applications, recommended that case backside temperature measured directly, least prototype setup. References: Thermalloy catalog #90-HS-11 (page 13), Figures EG&G Wakefield catalog, printed 4/90 (page 103), "115, 116, 117, Series SyncNut". Thermalloy catalog #90-HS-11 (page 12), "Test Results". Thermalloy catalog #90-HS-11 (page "Available Finishes". Thermalloy catalog #90-HS-11 (page 13), Figures Thermalloy catalog #90-HS-11 (page 106), "Test Method Comparison TO-3 Silicon Rubber Insulators". optional thermocouple hole will increase mounting thermal resistance significantly. difference cannot measured experimentally. Computer simulations indicate increase less than 0.02oC/W.
Junction Temp (TJ) Backside Case Temp (TC) Heat Sink
Flange Temp
Thermocouple (Spade-lug)
Thermocouple Hole (Drill size #51) Thermocouple (Omega fast response SDX-SET-RT-K-SMP)
FIGURE Package Case Thermal Measurement.
APPENDIX
MANUFACTURER BURR-BROWN CONCORD Cambion Mill-Max NEWARK Thermalloy AAVID Engineering EG&G Wakefield BERGQUIST Power Devices Crayotherm Alpha Wire Technology McMASTER-CARR ASMCO OMEGA TO-3 SOCKET 0804MC GAGE JACKS THERMAL GREASE THERMAL PADS HEAT SINKS TEFLON TUBING FASTENER HARDWARE TEMP MEAS TOOLS
TABLE Sources TO-3 Mounting Hardware. Alpha Wire Corp. Lidgerwood Ave. Elizabeth, 07207-0711 (908) 925-8000 ASMCO Baltimore Nutley, 07110 (201) 661-2600 AAVID Engineering, Inc. Kool Path P.O. 4000 Laconia, 03247 (603) 528-3400 BERGQUIST 5300 Edina Industrial Blvd. Minneapolis, 55435 (612) 835-2322 Cambion Division MIDLAND ROSS Alewife Place Cambridge, 02140 617) 491-5400 CONCORD Great Jones York, 10012 (212) 777-6571 Crayotherm Corp. 1185 Home Anaheim, 92806 (714) 630-2696 Technologies, Inc. 7855 Evans Road, Suite Scottsdale, 85260-3411 (602) 998-1484 EG&G Wakefield Audubon Road Wakefield, 01880 (617) 245-5900 McMASTER-CARR P.O. 54960 Angeles, 90054-0960 (213) 692-5911 Mill-Max Mfg. Corp. P.O. Pine Hollow Road Oyster Bay, 11771-0300 (516) 922-6000 NEWARK Electronics 4801 Ravenswood Ave. Chicago, 60640-4496 (312) 784-5100 OMEGA Omega Drive P.O. 4047 Stamford, 06907 (203) 359-1660 Power Devices 27071 Cabot Road, Bldg. Laguna Hills 92653 (714) 582-6712 Technology 4801 Ravenswood Ave. Chicago, 60640 (312) 907-5181 Thermalloy, Inc. 2021 Valley View Lane P.O. 810839 Dallas, 75381-0839 (214) 243-4321
information provided herein believed reliable; however, BURR-BROWN assumes responsibility inaccuracies omissions. BURR-BROWN assumes responsibility this information, such information shall entirely user's risk. Prices specifications subject change without notice. patent rights licenses circuits described herein implied granted third party. BURR-BROWN does authorize warrant BURR-BROWN product life support devices and/or systems.
IMPORTANT NOTICE Texas Instruments subsidiaries (TI) reserve right make changes their products discontinue product service without notice, advise customers obtain latest version relevant information verify, before placing orders, that information being relied current complete. products sold subject terms conditions sale supplied time order acknowledgment, including those pertaining warranty, patent infringement, limitation liability. warrants performance semiconductor products specifications applicable time sale accordance with TI's standard warranty. Testing other quality control techniques utilized extent deems necessary support this warranty. Specific testing parameters each device necessarily performed, except those mandated government requirements. Customers responsible their applications using components. order minimize risks associated with customer's applications, adequate design operating safeguards must provided customer minimize inherent procedural hazards. assumes liability applications assistance customer product design. does warrant represent that license, either express implied, granted under patent right, copyright, mask work right, other intellectual property right covering relating combination, machine, process which such semiconductor products services might used. TI's publication information regarding third party's products services does constitute TI's approval, warranty endorsement thereof.
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