APPLICATION NOTE
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Mounting Considerations
For Power Semiconductors
AN1040/D
Prepared by: Bill Roehr

INTRODUCTION
Current and power ratings of semiconductors are
inseparably linked to their thermal environment. Except forlead−mounted parts used at low currents, a heat exchanger
is required to prevent the junction temperature fromexceeding its rated limit, thereby running the risk of a highfailure rate. Furthermore, the semiconductor industry’s
field history indicated that the failure rate of most silicon
semiconductors decreases approximately by one−half for adecrease in junction temperature from 160°C to 135°C.(1)Guidelines for designers of military power supplies impose
a 110°C limit upon junction temperature.(2) Proper
mounting minimizes the temperature gradient between thesemiconductor case and the heat exchanger.
Most early life field failures of power semiconductors
can be traced to faulty mounting procedures. With metal
packaged devices, faulty mounting generally causes
unnecessarily high junction temperature, resulting in
reduced component lifetime, although mechanical damage
has occurred on occasion from improperly mounting to awarped surface. With the widespread use of various
plastic−packaged semiconductors, the prospect of
mechanical damage is very significant. Mechanicaldamage can impair the case moisture resistance or crack
the semiconductor die.
Figure 1 shows an example of doing nearly everything
wrong. A tab mount TO−220 package is shown being used
as a replacement for a TO−213AA (TO−66) part which was
socket mounted. To use the socket, the leads are bent − anoperation which, if not properly done, can crack the
package, break the internal bonding wires, or crack the die.
The package is fastened with a sheet−metal screw througha 1/4″ hole containing a fiber−insulating sleeve. The force
used to tighten the screw tends to pull the package into thehole, possibly causing enough distortion to crack the die. In
addition, the contact area is small because of the area
consumed by the large hole and the bowing of the package;© Semiconductor Components Industries, LLC, 2001

August, 2021 − Rev. 5

the result is a much higher junction temperature than
expected. If a rough heatsink surface and/or burrs aroundthe hole were displayed in the illustration, most but not all,poor mounting practices would be covered.
PLASTIC BODYLEADS
PACKAGE HEATSINKMICA WASHER

EQUIPMENTHEATSINK

SPEED NUT
(PART OF SOCKET)SOCKET FOR
TO−213AA PACKAGE SHEET METAL SCREW

Figure 1. Extreme Case of Improperly Mounting a
Semiconductor (Distortion Exaggerated)

In many situations, the case of the semiconductor mustbe electrically isolated from its mounting surface. The
isolation material is, to some extent, a thermal isolator as
well, which raises junction operating temperatures. In
addition, the possibility of arc−over problems is introduced
if high voltages are present. Various regulating agencies
also impose creepage distance specifications which further
complicates design. Electrical isolation thus places
additional demands upon the mounting procedure.
Proper mounting procedures usually necessitate orderly
attention to the following:
1. Preparing the mounting surface
2. Applying a thermal grease (if required)
3. Installing the insulator (if electrical isolation is desired)
4. Fastening the assembly
5. Connecting the terminals to the circuit

1

Publication Order Number:
AN1040/D

AN1040/D
Surface Finish

In this note, mounting procedures are discussed ingeneral terms for several generic classes of packages. As
newer packages are developed, it is probable that they will
fit into the generic classes discussed in this note. Uniquerequirements are given on data sheets pertaining to theparticular package. The following classes are defined:
Stud Mount
Flange Mount
Pressfit
Plastic Body Mount
Tab MountSurface Mount
Appendix A contains a brief review of thermal resistanceconcepts. Appendix B discusses measurement difficulties
with interface thermal resistance tests. Appendix C
indicates the type of accessories supplied by a number ofmanufacturers.

Surface finish is the average of the deviations both aboveand below the mean value of surface height. For minimum
interface resistance, a finish in the range of 50 to 60
microinches is satisfactory; a finer finish is costly toachieve and does not significantly lower contact resistance.
Tests conducted by Thermalloy, Inc., using a copper
TO−204 (TO−3) package with a typical 32−microinch
finish, showed that heatsink finishes between 16 and64 μ−in caused less than ± 2.5% difference in interface
thermal resistance when the voids and scratches were filledwith a thermal joint compound.(3) Most commerciallyavailable cast or extruded heatsinks will require spotfacing
when used in high−power applications. In general, milled
or machined surfaces are satisfactory if prepared with tools
in good working condition.
Mounting Holes

Mounting holes generally should only be large enough toallow clearance of the fastener. The larger thick flange typepackages having mounting holes removed from thesemiconductor die location, such as the TO−3, may
successfully be used with larger holes to accommodate an
insulating bushing, but many plastic encapsulated
packages are intolerant of this condition. For thesepackages, a smaller screw size must be used such that thehole for the bushing does not exceed the hole in the
package.
Punched mounting holes have been a source of trouble
because if not properly done, the area around a punchedhole is depressed in the process. This “crater” in theheatsink around the mounting hole can cause two
problems. The device can be damaged by distortion of the
package as the mounting pressure attempts to conform it to
the shape of the heatsink indentation, or the device may
only bridge the crater and leave a significant percentage of
its heat−dissipating surface out of contact with theheatsink. The first effect may often be detected
immediately by visual cracks in the package (if plastic), but
usually an unnatural stress is imposed, which results in an
early−life failure. The second effect results in hotter
operation and is not manifested until much later.
Although punched holes are seldom acceptable in therelatively thick material used for extruded aluminumheatsinks, several manufacturers are capable of properly
utilizing the capabilities inherent in both fine−edgeblanking or sheared−through holes when applied to sheet
metal as commonly used for stamped heatsinks. The holes
are pierced using Class A progressive dies mounted onfour−post die sets equipped with proper pressure pads andholding fixtures.

MOUNTING SURFACE PREPARATION
In general, the heatsink mounting surface should have aflatness and finish comparable to that of the semiconductor
package. In lower power applications, the heatsink surface
is satisfactory if it appears flat against a straight edge and is
free from deep scratches. In high−power applications, amore detailed examination of the surface is required.
Mounting holes and surface treatment must also be
considered.
Surface Flatness

Surface flatness is determined by comparing the variancein height (Δh) of the test specimen to that of a reference
standard as indicated in Figure 2. Flatness is normallyspecified as a fraction of the Total Indicator Reading (TIR).
The mounting surface flatness, i.e, Δh/TlR, if less than
4 mils per inch, normal for extruded aluminum, issatisfactory in most cases.
TIR = TOTAL INDICATOR READINGSAMPLEPIECEΔhÉÉÉÉÉÉÉÉÉÉÉÉÉÉ
ÉÉÉÉÉÉÉÉÉÉÉÉÉÉ
ÉÉÉÉÉÉÉÉÉÉÉÉÉÉTIRREFERENCE PIECEDEVICE MOUNTING AREA

Figure 2. Surface Flatness Measurement

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AN1040/D
To avoid using grease, manufacturers have developed
dry conductive and insulating pads to replace the more
traditional materials. These pads are conformal, therefore,
they partially fill voids when under pressure.

When mounting holes are drilled, a general practice withextruded aluminum, surface cleanup is important.
Chamfers must be avoided because they reduce heattransfer surface and increase mounting stress. However, theedges must be broken to remove burrs which cause poor
contact between device and heatsink and may punctureisolation material.

Thermal Compounds (Grease)

Joint compounds are a formulation of fine zinc or otherconductive particles in a silicone oil or other synthetic basefluid which maintains a grease−like consistency with time
and temperature. Since some of these compounds do not
spread well, they should be evenly applied in a very thinlayer using a spatula or lintless brush, and wiped lightly toremove excess material. Some cyclic rotation of the
package will help the compound spread evenly over theentire contact area. Some experimentation is necessary to
determine the correct quantity; too little will not fill all thevoids, while too much may permit some compound toremain between well−mated metal surfaces where it will
substantially increase the thermal resistance of the joint.
To determine the correct amount, several semiconductor
samples and heatsinks should be assembled with different
amounts of grease applied evenly to one side of eachmating surface. When the amount is correct, a very small
amount of grease should appear around the perimeter of
each mating surface as the assembly is slowly torqued to
the recommended value. Examination of a dismantled
assembly should reveal even wetting across each mating
surface. In production, assemblers should be trained toslowly apply the specified torque even though an excessive
amount of grease appears at the edges of mating surfaces.
Insufficient torque causes a significant increase in thethermal resistance of the interface.
To prevent accumulation of airborne particulate matter,
excess compound should be wiped away using a clothmoistened with acetone or alcohol. These solvents should
not contact plastic−encapsulated devices, as they may enter
the package and cause a leakage path or carry in substances
which might attack the semiconductor chip.
The silicone oil used in most greases has been found toevaporate from hot surfaces with time and become
deposited on other cooler surfaces. Consequently,
manufacturers must determine whether a microscopicallythin coating of silicone oil on the entire assembly will pose
any problems. It may be necessary to enclose components
using grease. The newer synthetic base greases show far
less tendency to migrate or creep than those made with asilicone oil base. However, their currently observed
working temperature range is less, they are slightly poorer
on thermal conductivity and dielectric strength and theircost is higher.

Surface Treatment

Many aluminum heatsinks are black−anodized to
improve radiation ability and prevent corrosion. Anodizing
results in significant electrical, but negligible thermal
insulation; it need only be removed from the mounting area
when electrical contact is required. Heatsinks are alsoavailable which have a nickel plated copper insert under
the semiconductor mounting area. No treatment of thissurface is necessary.
Another treated aluminum finish is iridite, or
chromateacid dip, which offers low resistance because of
its thin surface, yet has good electrical properties because it
resists oxidation. It need only be cleaned of the oils andfilms that collect in the manufacture and storage of thesinks, a practice which should be applied to all heatsinks.
For economy, paint is sometimes used for sinks; removalof the paint where the semiconductor is attached is usuallyrequired because of paint’s high thermal resistance.
However, when it is necessary to insulate thesemiconductor package from the heatsink, hard anodized
or painted surfaces allow an easy installation for low
voltage applications. Some manufacturers will provide
anodized or painted surfaces meeting specific insulation
voltage requirements, usually up to 400 volts.
It is also necessary that the surface be free from all
foreign material, film, and oxide (freshly bared aluminum
forms an oxide layer in a few seconds). Immediately prior
to assembly, it is a good practice to polish the mounting
area with No. 000 steel wool, followed by an acetone or
alcohol rinse.
INTERFACE DECISIONS
When any significant amount of power is being
dissipated, something must be done to fill the air voids
between mating surfaces in the thermal path. Otherwise,
the interface thermal resistance will be unnecessarily highand quite dependent upon the surface finishes.
For several years, thermal joint compounds, often called
grease, have been used in the interface. They have aresistivity of approximately 60°C/W/in whereas air has
1200°C/W/in. Since surfaces are highly pock−marked withminute voids, use of a compound makes a significant
reduction in the interface thermal resistance of the joint.
However, the grease causes a number of problems, as
discussed in the following section.

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AN1040/D
greased bare joint and a joint using Grafoil®, a drygraphite compound, is shown in the data of Figure 3
through Figure 6. Grafoil is claimed to be a replacement for
grease when no electrical isolation is required; the data
indicates it does indeed perform as well as grease. Anotherconductive pad available from Aavid is called Kon−Duxt.
It is made with a unique, grain oriented, flake−likestructure (patent pending). Highly compressible, it
becomes formed to the surface roughness of both theheatsink and semiconductor. Manufacturer’s data shows it
to provide an interface thermal resistance better than ametal interface with filled silicone grease. Similar dry
conductive pads are available from other manufacturers.
They are a fairly recent development; long term problems,
if they exist, have not yet become evident.

Data showing the effect of compounds on several
package types under different mounting conditions isshown in Table 1. The rougher the surface, the morevaluable the grease becomes in lowering contact
resistance; therefore, when mica insulating washers areused, use of grease is generally mandatory. The joint
compound also improves the breakdown rating of theinsulator.
Conductive Pads

Because of the difficulty of assembly using grease andthe evaporation problem, some equipment manufacturers
will not, or cannot, use grease. To minimize the need for
grease, several vendors offer dry conductive pads whichapproximate performance obtained with grease. Data for a

Table 1. Approximate Values for Interface Thermal Resistance Data from Measurements Performed
in onsemi Applications Engineering Laboratory
Dry interface values are subject to wide variation because of extreme dependence upon surface conditions.
Unless otherwise noted, the case temperature is monitored by a thermocouple located directly under the die reached througha hole in the heatsink. (See Appendix B for a discussion of Interface Thermal Resistance Measurements.)
Interface Thermal Resistance (°C/W)
Package Type and Data
JEDEC
Outlines

Description

DO−203AA, TO−210AA
TO−208AB

Metal−to−Metal

With Insulator

Test Torque
In−Lb

Dry

Lubed

Dry

Lubed

Type

10−32 Stud
7/16″ Hex

15

0.3

0.2

1.6

0.8

3 mil
Mica

DO−203AB, TO−210AC
TO−208

1/4−28 Stud
11/16″ Hex

25

0.2

0.1

0.8

0.6

5 mil
Mica

DO−208AA

Pressfit, 1/2″

−

0.15

0.1

−

−

−

TO−204AA (TO−3)

Diamond Flange

6

0.5

0.1

1.3

0.36

3 mil
Mica

TO−213AA (TO−66)

Diamond Flange

6

1.5

0.5

2.3

0.9

2 mil
Mica

TO−126

Thermopad
1/4″ x 3/8″

6

2.0

1.3

4.3

3.3

2 mil
Mica

TO−220AB

Thermowatt

8

1.2

1.0

3.4

1.6

2 mil
Mica

See
Note

1

1, 2

NOTES: 1. See Figure 3 through Figure 7 for additional data on TO−3 and TO−220 packages.
2. Screw not insulated. See Figure 20.

INSULATION CONSIDERATIONS
Since most power semiconductors use vertical device
construction, it is common to manufacture power
semiconductors with the output electrode (anode, collector
or drain) electrically common to the case; the problem ofisolating this terminal from ground is a common one. For
lowest overall thermal resistance, which is quite importantwhen high power must be dissipated, it is best to isolate theentire heatsink/semiconductor structure from ground,rather than to use an insulator between the semiconductor
and the heatsink. Heatsink isolation is not always possible,
however, because of EMI requirements, safety reasons,instances where a chassis serves as a heatsink or where aheatsink is common to several non−isolated packages. In

these situations, insulators are used to isolate the individualcomponents from the heatsink. Newer packages, such as
the onsemi FULLPAKt and EMS modules, contain theelectrical isolation material within, thereby saving theequipment manufacturer the burden of addressing theisolation problem.
Insulator Thermal Resistance

When an insulator is used, thermal grease is of greater
importance than with a metal−to−metal contact, because twointerfaces exist instead of one and some materials, such as
mica, have a hard, markedly uneven surface. With many
isolation materials, reduction of interface thermal resistanceof between 2 to 1 and 3 to 1 are typical when grease is used.

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4AN1040/D

THERMAL RESISTANCE FROM TRANSISTOR CASE
TO MOUNTING SURFACE, R θ CS ( C/WATT)
°

2

1.6
(1)

1.4

(2)
(3)
(4)
(5)

1.2
1
0.8
0.6

(6)
(7)

0.4

(1) Thermafilm, .002 (.05) thick.
(2) Mica, .003 (.08) thick.
(3) Mica, .002 (.05) thick.
(4) Hard anodized, .020 (.51)
thick.
(5) Aluminum oxide, .062 (1.57)
thick.
(6) Beryllium oxide, .062 (1.57)
thick.
(7) Bare joint − no finish.
(8) Grafoil, .005 (.13) thick.**Grafoil is not an insulating material.

0.2
(8)

0

THERMAL RESISTANCE FROM TRANSISTOR CASE
TO MOUNTING SURFACE, R θ CS ( C/WATT)

highly toxic.) Thermafilm® is a filled polymide material
which is used for isolation (variation of Kapton®). It is a
popular material for low power applications because of its
low cost ability to withstand high temperatures, and ease ofhandling in contrast to mica which chips and flakes easily.
A number of other insulating materials are also shown.
They cover a wide range of insulation resistance, thermal
resistance and ease of handling. Mica has been widely usedin the past because it offers high breakdown voltage andfairly low thermal resistance at a low cost, but it certainly
should be used with grease.

Data obtained by Thermalloy, showing interface
resistance for different insulators and torques applied toTO−204 (TO−3) and TO−220 packages, are shown in
Figure 3 through Figure 6, for bare and greased surfaces.
Similar materials to those shown are available from several
manufacturers. It is obvious that with some arrangements,
the interface thermal resistance exceeds that of thesemiconductor (junction to case).
Referring to Figure 3 through Figure 6, one may
conclude that when high power is handled, beryllium oxide
is unquestionably the best. However, it is an expensive
choice. (It should not be cut or abraded, as the dust is

°

1
0.9
0.8
0.7
0.6

0.4

(2)
(3)
(5)
(4)

0.3
0.2

(6)
(7)

0.1
0

0

1
2
3
4
5
6
MOUNTING SCREW TORQUE (IN-LBS)

0

1
2
3
4
5
6
MOUNTING SCREW TORQUE (IN-LBS)072
145 217 290 362
INTERFACE PRESSURE (psi)072
145 217 290 362
INTERFACE PRESSURE (psi)

435

5
(1)
4

°

(2)
(3)
(4)

3

2

(1) Thermafilm, .002 (.05) thick.
(2) Mica, .003 (.08) thick.
(3) Mica, .002 (.05) thick.
(4) Hard anodized, .020 (.51)
thick.
(5) Thermasil II, .009 (.23)
thick.
(6) Thermasil III, .007‘6 (.15)
thick.
(7) Bare joint − no finish.
(8) Grafoil, .005 (.13) thick.*(5)(6)(7) *Grafoil is not an insulating material.
(8)

1

0
0

435

Figure 4. TO−204AA (TO−3) With
Thermal Grease12 (IN-LBS) 456
MOUNTING SCREW TORQUE (IN-LBS)

THERMAL RESISTANCE FROM TRANSISTOR CASE
TO MOUNTING SURFACE, R θ CS ( C/WATT)

Figure 3. TO−204AA (TO−3)
Without Thermal Grease

THERMAL RESISTANCE FROM TRANSISTOR CASE
TO MOUNTING SURFACE, R θ CS ( C/WATT)

(1)

0.5

5

4

°

3
(1)
2
(2)
(3)
(4)
1
(7)
0
0

4
1
2
3
5
6
MOUNTING SCREW TORQUE (IN-LBS)

Figure 6. TO−220 With Thermal Grease

Figure 5. TO−220 Without Thermal Grease

INTERFACE THERMAL RESISTANCE FOR TO−204, TO−3, AND TO−220 PACKAGES USING DIFFERENTINSULATING MATERIALS AS A FUNCTION OF MOUNTING SCREW TORQUE (DATA COURTESY THERMALLOY)

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AN1040/D
Silicone rubber insulators have gained favor because
they are somewhat conformal under pressure. Their ability
to fill in most of the metal voids at the interface reduces theneed for thermal grease. When first introduced, they
suffered from cut−through after a few years in service. The
ones presently available have solved this problem byhaving imbedded pads of Kapton or fiberglass. By
comparing Figure 5 and Figure 6, it can be noted that
Thermasilt, a filled silicone rubber, without grease, has
about the same interface thermal resistance as greased mica
for the TO−220 package.
A number of manufacturers offer silicone rubber
insulators. Table 2 shows measured performance of anumber of these insulators under carefully controlled,
nearly identical conditions. The interface thermal
resistance extremes are over 2:1 for the various materials.
It is also clear that some of the insulators are much moretolerant than others of out−of−flat surfaces. Since the tests
were performed, newer products have been introduced.
The Bergquist K−10® pad, for example, is described ashaving about 2/3 the interface resistance of the Sil−Pad®
1000 which would place its performance close to the
Chomerics 1671 pad. Aavid also offers an isolated padcalled Rubber−Duct, however, it is only available
vulcanized to a heatsink and, therefore, was not included in
the comparison. Published data from Aavid shows RθCS
below 0.3°C/W for pressures above 500 psi. However,surface flatness and other details are not specified, so a
comparison cannot be made with other data in this note.

for Thermasil III to exceed the performance of greased
mica, total surface flatness must be under 2 mils, a situationthat requires spot finishing.

Table 2. Thermal Resistance of Silicone Rubber Pads

Silicon rubber insulators have a number of unusual
characteristics. Besides being affected by surface flatness
and initial contact pressure, time is a factor. For example, ina study of the CHO−THERM® 1688 pad thermal interface
impedance dropped from 0.90°C/W to 0.70°C/W at the endof 1000 hours. Most of the change occurred during the first
200 hours where RθCS measured 0.74°C/W. The torque on
the conventional mounting hardware had decreased to
3 in−lb from an initial 6 in−lb. With nonconformalmaterials, a reduction in torque would have increased theinterface thermal resistance.
Because of the difficulties in controlling all variables
affecting tests of interface thermal resistance, data fromdifferent manufacturers is not in good agreement. Table 3
shows data obtained from two sources. The relative
performance is the same, except for mica which varies
widely in thickness. Appendix B discusses the variables
which need to be controlled. At the time of this writing,
ASTM Committee D9 is developing a standard forinterface measurements.
The conclusions to be drawn from all this data is thatsome types of silicon rubber pads, mounted dry, will
outperform the commonly used mica with grease. Cost
may be a determining factor in making a selection.

Manufacturer

Product

RθCS @
3 Mils*RθCS @
7.5 Mils*

Wakefield
Bergquist
Stockwell Rubber
Bergquist
ThermalloyShin−Etsu
Bergquist
Chomerics
Wakefield
Bergquist
Ablestik
Thermalloy
Chomerics

Delta Pad 173−7
Sil−Pad K−4®
1867
Sil−Pad 400−9®
Thermasil II
TC−30AG
Sil−Pad 400−7®
1674
Delta Pad 174−9
Sil−Pad 1000®
Thermal Wafers
Thermasil III
1671

.790
.752
.742
.735
.680
.664
.633
.592
.574
.529
.500
.440
.367

1.175
1.470
1.015
1.205
1.045
1.260
1.060
1.190
.755
.935
.990
1.035
.655

INTERFACE THERMAL RESISTANCE ( C/W)

1.2

(1)

1

(2)

°

0.8

0.6

0.4

(1) Thermasil II, .009 inches (.23) thick.
(2) Thermasil III, .006 inches (.15) thick.

0.2

0
0

0.002
0.004
0.006
0.008
0.01
TOTAL JOINT DEVIATION FROM FLAT OVER
TO-3 HEADER SURFACE AREA (INCHES)
Data courtesy of Thermalloy

Figure 7. Effect of Total Surface Flatness on
Interface Resistance Using Silicon Rubber Insulators*Test Fixture Deviation from flat from Thermalloy EIR86−1010.

The thermal resistance of some silicone rubber insulators
is sensitive to surface flatness when used under a fairly
rigid base package. Data for a TO−204AA (TO−3) package
insulated with Thermasil is shown in Figure 7. Observethat the “worst case” encountered (7.5 mils) yields results
having about twice the thermal resistance of the “typicalcase” (3 mils), for the more conductive insulator. In order

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AN1040/D
Table 3. Performance of Silicon Rubber Insulators
Tested Per MIL−I−49456

The newer insulated packages can be grouped into two
categories. The first has insulation between thesemiconductor chips and the mounting base; an exposedarea of the mounting base is used to secure the part. The
Energy Management Series (EMS) modules, shown in
Figure 16, Case 806 (ICePAKt) and Case 388A
(TO−258AA) (see Figure 16) are examples of parts in thiscategory. The second category contains parts which have aplastic overmold covering the metal mounting base. The
isolated, Case 221C, illustrated in 21, is an example ofparts in the second category.
Parts in the first category (those with an exposed metal
flange or tab) are mounted the same as their non−insulated
counterparts. However, as with any mounting system
where pressure is bearing on plastic, the overmolded typeshould be used with a conical compression washer,described later in this note.

Measured Thermal Resistance(°C/W)
Material

Thermalloy
Data(1)

Bergquist
Data(2)

0.033
0.082
0.233
−
0.263
0.267
0.329
0.400
0.433
0.500
0.533
0.583

0.008
−
−
0.009
0.200
−
0.400
0.300
−
−
0.440
0.440

Bare Joint, greased
BeO, greased
CHO−THERM, 1617
Q Pad (non−insulated)
Sil−Pad, K−10
Thermasil III
Mica, greased
Sil−Pad 1000
CHO−THERM 1674
Thermasil II
Sil−Pad 400
Sil−Pad K−4(1) From Thermalloy EIR 87−1030(2) From Bergquist Data Sheet

FASTENER AND HARDWARE
CHARACTERISTICS
Characteristics of fasteners, associated hardware, and thetools to secure them determine their suitability for use inmounting the various packages. Since many problems havearisen because of improper choices, the basic
characteristics of several types of hardware are discussed
next.

Insulation Resistance

When using insulators, care must be taken to keep thematting surfaces clean. Small particles of foreign mattercan puncture the insulation, rendering it useless orseriously lowering its dielectric strength. In addition,
particularly when voltages higher than 300 V are
encountered, problems with creepage may occur. Dust andother foreign material can shorten creepage distances
significantly; so having a clean assembly area is important.
Surface roughness and humidity also lower insulation
resistance. Use of thermal grease usually raises thewithstand voltage of the insulation system, but excess must
be removed to avoid collecting dust. Because of thesefactors, which are not amenable to analysis, hi−pot testingshould be done on prototypes and a large margin of safety
employed.

Compression Hardware

Normal split ring lock washers are not the best choice formounting power semiconductors. A typical #6 washer
flattens at about 50 pounds, whereas 150 to 300 pounds isneeded for good heat transfer at the interface. A very usefulpiece of hardware is the conical, sometimes called a
Belleville washer, compression washer. As shown in
Figure 8, it has the ability to maintain a fairly constantpressure over a wide range of its physical deflection −generally 20% to 80%. When installing, the assembler
applies torque until the washer depresses to half its original
height. (Tests should be run prior to setting up the assemblyline to determine the proper torque for the fastener used toachieve 50% deflection.) The washer will absorb any
cyclic expansion of the package, insulating washer or othermaterials caused by temperature changes. Conical washers
are the key to successful mounting of devices requiring
strict control of the mounting force or when plastic
hardware is used in the mounting scheme. They are usedwith the large face contacting the packages. A newvariation of the conical washer includes it as part of a nut
assembly. Called a “sync nut,” the patented device can besoldered to a PC board and the semiconductor mountedwith a 6−32 machine screw.(4)Insulated Electrode Packages

Because of the nuisance of handling and installing theaccessories needed for an insulated semiconductor
mounting, equipment manufacturers have longed forcost−effective insulated packages since the 1950’s. The
first to appear were stud mount types which usually have alayer of beryllium oxide between the stud hex and the can.
Although effective, the assembly is costly and requires
manual mounting and lead wire soldering to terminals on
top of the case. In the late 80’s, a number of electricallyisolated parts became available from various
semiconductor manufacturers. These offerings presently
consist of multiple chips and integrated circuits as well as
the more conventional single chip devices.

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AN1040/D

200

result. When standard sheet metal screws are used, theymust be used in a clearance hole to engage a speednut. If aself−tapping process is desired, the screw type must be
used which roll−forms machine screw threads.

160

Rivets

PRESSURE ON PACKAGE (LB‐F)

280
240

Rivets are not a recommended fastener for any of theplastic packages. When a rugged metal flange−mountpackage or EMS module is being mounted directly to aheatsink, rivets can be used provided press−riveting isused. Crimping force must be applied slowly and evenly.
Pop−riveting should never be used because the highcrimping force could cause deformation of mostsemiconductor packages. Aluminum rivets are muchpreferred over steel because less pressure is required to set
the rivet and thermal conductivity is improved.
The hollow rivet, or eyelet, is preferred over solid rivets.
An adjustable, regulated pressure press is used such that a
gradually increasing pressure is used to pan the eyelet. Useof sharp blows could damage the semiconductor die.

120
80
40
0
0

20
40
60
80
DEFLECTION OF WASHER DURING MOUNTING (%)

100

Figure 8. Characteristics of the ConicalCompression Washers Designed for Use with
Plastic Body Mounted Semiconductors
Clips

Fast assembly is accomplished with clips. When only a
few watts are being dissipated, the small board−mounted orfree−standing heat dissipaters with an integral clip, offeredby several manufacturers, result in a low cost assembly.
When higher power is being handled, a separate clip may
be used with larger heatsinks. In order to provide properpressure, the clip must be specially designed for aparticular heatsink thickness and semiconductor package.
Clips are especially popular with plastic packages suchas the TO−220 and TO−126. In addition to fast assembly,
the clip provides lower interface thermal resistance thanother assembly methods when it is designed for properpressure to bear on the top of the plastic over the die. The
TO−220 package usually is lifted up under the die location
when mounted with a single fastener through the hole in
the tab because of the high pressure at one end.

Solder

Until the advent of the surface mount assembly
technique, solder was not considered a suitable fastener for
power semiconductors. However, user demand has led tothe development of new packages for this application.
Acceptable soldering methods include conventionalbelt−furnace, irons, vapor−phase reflow, and infrared
reflow. It is important that the semiconductor temperature
not exceed the specified maximum (usually 260°C) or thedie bond to the case could be damaged. A degraded diebond has excessive thermal resistance which often leads toa failure under power cycling.
Adhesives

Adhesives are available which have coefficients ofexpansion compatible with copper and aluminum.(5)Highly conductive types are available; a 10 mil layer has
approximately 0.3°C/W interface thermal resistance.
Different types are offered: high strength types fornon−field serviceable systems or low strength types forfield serviceable systems. Adhesive bonding is attractive
when case−mounted parts are used in wave soldering
assembly because thermal greases are not compatible withthe conformal coatings used and the greases foul the solder
process.

Machine Screws

Machine screws, conical washers, and nuts (or sync nuts)
can form a trouble−free fastener system for all types of
packages which have mounting holes. However, proper
torque is necessary. Torque ratings apply when dry;
therefore, care must be exercised when using thermal
grease to prevent it from getting on the threads asinconsistent torque readings result. Machine screw heads
should not directly contact the surface of plastic packages
types as the screw heads are not sufficiently flat to provide
properly distributed force. Without a washer, cracking of
the plastic case could occur.

Plastic Hardware

Most plastic materials will flow, but differ widely in thischaracteristic. When plastic materials form parts of thefastening system, compression washers are highly valuable
to assure that the assembly will not loosen with time andtemperature cycling. As previously discussed, loss ofcontact pressure will increase interface thermal resistance.

Self−Tapping Screws

Under carefully controlled conditions, sheet−metalscrews are acceptable. However, during the tapping
process with a standard screw, a volcano−like protrusion
will develop in the metal being threaded; an unacceptablesurface that could increase the thermal resistance may

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AN1040/D
FASTENING TECHNIQUES

Bending can be minimized by:
1. Mounting the component parallel to the heatsink fins toprovide increased stiffness.
2. Allowing the heatsink holes to be a bit oversized sothat some can slip between surfaces as the temperaturechanges.
3. Using a highly conductive thermal grease or mounting
pad between the heatsink and semiconductor tominimize the temperature gradient and allow for
movement.

Each of the various classes of packages in use requires
different fastening techniques. Details pertaining to eachtype are discussed in the following sections. Some generalconsiderations follow.
To prevent galvanic action from occurring when devices
are used on aluminum heatsinks in a corrosive atmosphere,
many devices are nickel− or gold−plated. Consequently,
precautions must be taken not to mar the finish.
Another factor to be considered is that when acopper−based part is rigidly mounted to an aluminumheatsink, a bi−metallic system results which will bend withtemperature changes. Not only is the thermal coefficient ofexpansion different for copper and aluminum, but thetemperature gradient through each metal also causes eachcomponent to bend. If bending is excessive and the
package is mounted by two or more screws, thesemiconductor chip could be damaged.

CASE 42A(DO−5)

CASE 56−03
DO−203AA(DO−4)

CASE 245(DO−4)

Stud Mount

Parts which fall into the stud−mount classification are
shown in Figure 8 through Figure 11. Mounting errors with
non−insulated stud−mounted parts are generally confined
to application of excessive torque or tapping the stud into a
threaded heatsink hole. Both of these practices may cause awarpage of the hex base which may crack thesemiconductor die. The only recommended fastening
method is to use a nut and washer. The details are shown in
Figure 12.

CASE 257
DO−203AB(DO−5)

CASE 263−04

Figure 9. Standard Non−Isolated Types

CASE 144B−05(.380″ STUD)CASE 145A−09(.380″ STUD)CASE 145A−10(.500″ STUD)CASE 244−04(.280″ STUD)

Figure 10. Isolated Type

CASE 305−01(.204″ STUD)

Figure 11. RF Stripline Opposed Emitter (SOE) Series
A VARIETY OF STUD−MOUNT PARTS

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9

CASE 311−02

CASE 332−04(.380″ STUD)AN1040/D
CHAMFER
0.01 NOM.
SHOULDER RING
0.501
0.505 DIA.

0.01 NOM.
HEATSINK

0.24

INSULATOR

0.0499 ± 0.001 DIA.

TEFLON BUSHINGHEATSINK MOUNTINGCHASSISADDITIONALHEATSINK PLATE

RIVET

INSULATORFLAT STEEL WASHERSOLDER TERMINALINTIMATECONTACT AREACOMPLETEKNURL CONTACT
AREA

THIN CHASSIS

THIN−CHASSIS MOUNTINGCONICAL WASHER

The hole edge must be chamfered as shown to prevent
shearing off the knurled edge of the case during press−in. The
pressing force should be applied evenly on the shoulder ringto avoid tilting or canting of the case in the hole during thepressing operation. Also, the use of a thermal joint compound
will be of considerable aid. The pressing force will vary from
250 to 1000 pounds, depending upon the heatsink material.
Recommended hardnesses are: copper−less than 50 on the
Rockwell F scale; aluminum−less than 65 on the Brinell scale.
A heatsink as thin as 1/8″ may be used, but the interface thermal resistance will increase in direct proportion to the contact
area. A thin chassis requires the addition of a backup plate.

HEX NUT

Figure 12. Isolating Hardware Used fora Non−Isolated Stud−Mount Package

Insulated electrode packages on a stud mount baserequire less hardware. They are mounted the same as their
non−insulated counterparts, but care must be exercised to
avoid applying a shear or tension stress to the insulation
layer, usually a beryllium oxide (BeO) ceramic. Thisrequirement dictates that the leads must be attached to thecircuit with flexible wire. In addition, the stud hex should
be used to hold the part while the nut is torqued.
RF transistors in the stud−mount Stripline Opposed
Emitter (SOE) package impose some additional constraints
because of the unique construction of the package. Special
techniques to make connections to the stripline leads and to
mount the part so no tension or shear forces are applied to
any ceramic − metal interface are discussed in the section
entitled, “Connecting and Handling Terminals.”

Figure 13. Press−Fit Package
Flange Mount

A large variety of parts fit into the flange mount category
as shown in Figure 14 through Figure 17. Few known
mounting difficulties exist with the smaller flange mountpackages, such as the TO−204 (TO−3). The rugged baseand distance between die and mounting holes combine to
make it extremely difficult to cause any warpage unless
mounted on a surface which is badly bowed or unless one
side is tightened excessively before the other screw isstarted. It is, therefore, good practice to alternate tighteningof the screws so that pressure is evenly applied. After thescrews are finger−tight, the hardware should be torqued toits final specification in at least two sequential steps. A
typical mounting installation for a popular flange type partis shown in Figure 18. Machine screws (preferred),self−tapping screws, eyelets, or rivets may be used tosecure the package using guidelines in the previous section,“Fastener and Hardware Characteristics.”

Press Fit

For most applications, the press−fit case should be
mounted according to the instructions shown in Figure 13.
A special fixture, meeting the necessary requirements,
must be used.

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AN1040/D
a ceramic (BeO) substrate is attached to a relatively thin,fairly long, flange. The maximum allowable flange
bending to avoid mechanical damage has been determinedand presented in detail in Engineering Bulletin EB107/D,“Mounting Considerations for onsemi RF Power
Modules.” Many of the parts can handle a combinedheatsink and flange deviation from flat of 7 to 8 mils whichis commonly available. Others must be held to 1.5 mils,
which requires that the heatsink have nearly perfectflatness.

The copper flange of the Energy Management Series(EMS) modules is very thick. Consequently, the parts arerugged and indestructible for all practical purposes. No
special precautions are necessary when fastening theseparts to a heatsink.
Some packages specify a tightening procedure. For
example, with the Power Tap package, 15, final torqueshould be applied first to the center position.
The RF power modules (MHW series) are more sensitive
to the flatness of the heatsink than other packages because

CASE 1, 11
TO−204AA(TO−3)

CASE 357C

CASE 383

Figure 14. TO−3 Variations

CASE 373

CASE 807

CASE 211

CASE 211

CASE 215

Figure 15. Plastic PowerTap

CASE 807A

CASE 316

CASE 319(CS−12)

CASE 328A

CASE 333

CASE 333A(MAAC PAC)

CASE 336

CASE 368(HOG PAC)

CASE 744A

CASE 808

CASE 809

CASE 812

CASE 813

CASE 814B

CASE 816

CASE 819

CASE 337

Figure 16. Energy Management Series (Isolated Base Plate)Figure 17. RF Stripline Isolated Output Opposed
Emitter (SOE) Series

A LARGE ARRAY OF PARTS FIT INTO THE FLANGE−MOUNT CLASSIFICATION

is a common problem. In some parts returned for failure
analysis, indentions up to 10 mils deep in the mounting
screw areas, have been observed.
Calculations indicate that the length of the flange
increases in excess of two mils with a temperature changeof 75°C. In such cases, if the mounting screw torque isexcessive, the flange is prevented from expanding inlength; instead, it bends upward in the mid−section,
cracking the BeO and the die. A similar result can also
occur during the initial mounting of the device if anexcessive amount of thermal compound is applied. With

Specific mounting recommendations are critical to RF
devices in isolated packages because of the internal
ceramic substrate. The large area, Case 368−03 (HOG
PAC), will be used to illustrate problem areas. It is moresensitive to proper mounting techniques than most otherRF power devices.
Although the data sheets contain information on
recommended mounting procedures, experience indicatesthat they are often ignored. For example, the recommended
maximum torque on the 4−40 mounting screws is 5 in./lbs.
Spring and flat washers are recommended. Over−torquingwww.onsemi.com
11

AN1040/D
Use of the washer is only important when the size of themounting hole exceeds 0.140 in. (6−32 clearance). Larger
holes are needed to accommodate the lower insulatingbushing when the screw is electrically connected to thecase; however, the holes should not be larger thannecessary to provide hardware clearance and should neverexceed a diameter of 0.250 inch. Flange distortion is also
possible if excessive torque is used during mounting. A
maximum torque of 8 in./lbs is suggested when using a6−32 screw.
Care should be exercised to assure that the tool used todrive the mounting screw never comes in contact with theplastic body during the driving operation. Such contact can
result in damage to the plastic body and internal device
connections. To minimize this problem, onsemi TO−220
packages have a chamfer on one end. TO−220 packages ofother manufacturers may need a spacer or combination
spacer and isolation bushing to raise the screw head above
the top surface of the plastic.

sufficient torque, the thermal compound will squeeze outof the mounting hole areas, but will remain under the centerof the flange, deforming it. Deformations of 2 − 3 mils havebeen measured between the center and the ends under suchconditions (enough to crack internal ceramic).
Another problem arises because the thickness of theflange changes with temperature. For the 75°C temperature
excursion mentioned, the increased amount is around0.25 mils which results in further tightening of themounting screws, thus increasing the effective torque fromthe initial value. With a decrease in temperature, theopposite effect occurs. Therefore, thermal cycling not only
causes risk of structural damage but often causes theassembly to loosen which raises the interface resistance.
Use of compression hardware can eliminate this problem.
NO. 6 SHEET METAL SCREWS

POWER
TRANSISTORINSULATORCASE 221A−04(TO−220AB)

CASE 221B−03(TO−220AC)

INSULATING
BUSHINGHEATSINKCASE 314B(5 PIN TO−220)

SOCKET

CASE 340−02(TO−218)

Figure 18. Hardware Used for a TO−204AA (TO−3)
Flange Mount Part

CASE 314D

CASE 387−01(TO−254AA)
CASE 388A−01(TO−258AA)

CASE 339

CASE 806−05(ICePAK)Figure 19. Several Types of Tab−Mount Parts

Tab Mount

The popular TO−220 Package and others of similar
construction lift off the mounting surface as pressure isapplied to one end. (See Appendix B, Figure 36.) To
counter this tendency, at least one hardware manufacturer
offers a hard plastic cantilever beam which applies moreeven pressure on the tab.(6) In addition, it separates themounting screw from the metal tab. Tab mount parts may

The tab mount class is composed of a wide array of
packages as illustrated in Figure 19. Mounting
considerations for all varieties are similar to that for the
popular TO−220 package, whose suggested mounting
arrangements and hardware are shown in Figure 20. The
rectangular washer shown in Figure 20a is used tominimize distortion of the mounting flange; excessive
distortion could cause damage to the semiconductor chip.

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AN1040/D
Plastic Body Mountalso be effectively mounted with clips as shown in
Figure 27.
To obtain high pressure without cracking the case, apressure spreader bar should be used under the clip.
Interface thermal resistance with the cantilever beam orclips can be lower than with screw mounting.
The ICePAK (Case 806−05) is basically an elongatedTO−220 package with isolated chips. The mounting
precautions for the TO−220 consequently apply. In
addition, since two mounting screws are required, thealternate tightening procedure described for the flange
mount package should be used.
In situations where a tab mount package is making directcontact with the heatsink, an eyelet may be used, provided
sharp blows or impact shock is avoided.
a) Preferred Arrangement
for Isolated or Non−isolated
Mounting. Screw is at
Semiconductor Case
Potential. 6−32 Hardware is
Used.

The Thermopadt and isolated plastic power packages
shown in Figure 21 are typical of packages in this group.
They have been designed to feature minimum size with nocompromise in thermal resistance. For the Thermopad(Case 77) parts, this is accomplished by die−bonding thesilicon chip on one side of a thin copper sheet; the opposite
side is exposed as a mounting surface. The copper sheet has
a hole for mounting; plastic is molded enveloping the chip
but leaving the mounting hole open. The low thermal
resistance of this construction is obtained at the expense ofa requirement that strict attention be paid to the mounting
procedure.
The isolated (Case 221C−02) is similar to a TO−220
except that the tab is encased in plastic. Because themounting force is applied to plastic, the mounting
procedure differs from a standard TO−220 and is similar tothat of the Thermopad.

b) Alternate Arrangement
for Isolated Mounting when
Screw must be at Heatsink
Potential. 4−40 Hardware is
Used.

CASE 77
TO−225AA/TO−126(THERMOPAD)

Use Parts Listed Below

Choose from Parts Listed
Below4-40 PAN OR HEX HEAD SCREW
6-32 HEXHEAD SCREWCASE 221C−02(FULLY ISOLATED)FLAT WASHERINSULATING BUSHING(1) RECTANGULAR STEEL WASHERSEMICONDUCTOR(CASE 221, 221A)

CASE 221D−02(FULLY ISOLATED)SEMICONDUCTOR(CASE 221, 221A)(2) RECTANGULAR
 INSULATORHEATSINK

CASE 340B−03(FULLY ISOLATED)RECTANGULAR
INSULATOR(2) BUSHINGHEATSINK(3) FLAT WASHERCOMPRESSION WASHER

Figure 21. Plastic Body−Mount Packages(4) CONICAL WASHER
6-32 HEX NUT
4-40 HEX NUT(1) Used with thin chassis and/or large hole.
(2) Used when isolation is required.
(3) Required when nylon bushing is used.

Figure 20. Mounting Arrangements for
Tab Mount TO−220

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AN1040/D
resistance is about the same for either method. This occurs
because the clip bears directly on top of the die and holds
the package flat while the screw causes the package to lift
up somewhat under the die. (See Figure 36 of Appendix B.)
The interface should consist of a layer of thermal grease ora highly conductive thermal pad. Of course, screw
mounting shown in Figure 26 may also be used, but aconical compression washer should be included. Bothmethods afford a major reduction in hardware as comparedto the conventional mounting method with a TO−220
package which is shown in Figure 25.

Several types of fasteners may be used to secure thesepackages; machine screws, eyelets, or clips are preferred.
With screws or eyelets, a conical washer should be usedwhich applies the proper force to the package over a fairly
wide range of deflection and distributes the force over afairly large surface area. Screws should not be tightenedwith any type of air−driven torque gun or equipment which
may cause high impact. Characteristics of a suitableconical washer is shown in Figure 8.
Figure 22 through Figure 24 shows details of mounting
Case 77 devices. Clip mounting is fast and requires
minimum hardware, however, the clip must be properlychosen to insure that the proper mounting force is applied.
When electrical isolation is required with screw mounting,a bushing inside the mounting hole will insure that thescrew threads do not contact the metal base.
The isolated, (Case 221C, 221D, and 340B) permits themounting procedure to be greatly simplified over that of astandard TO−220. As shown in Figure 27, one properlychosen clip, inserted into two slotted holes in the heatsink,is all the hardware needed. Even though clip pressure ismuch lower than obtained with a screw, the thermal

Surface Mount

Although many of the tab mount parts have been surface
mounted, special small footprint packages for mounting
power semiconductors using surface mount assembly
techniques have been developed. The DPAK, shown in
Figure 28, for example, will accommodate a die up to
112 mils x 112 mils, and has a typical thermal resistancearound 2°C/W junction to case. The thermal resistancevalues of the solder interface is well under 1°C/W. The
printed circuit board also serves as the heatsink.

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AN1040/D
MACHINE SCREW ORSHEET METAL SCREW
4−40 SCREWHEATSINK
SURFACECOMPRESSION WASHER

PLAIN WASHERTHERMOPAD PACKAGEINSULATING BUSHING

INSULATING WASHER(OPTIONAL)
MACHINE OR SPEED
NUT

INSULATORHEATSINK

Figure 22. Machine Screw Mounting

COMPRESSION WASHER
NUT

EYELET

Figure 25. Screw−Mounted TO−220
6−32 SCREWPLAIN WASHERCOMPRESSIONWASHER
INSULATING WASHER(OPTIONAL)HEATSINKCOMPRESSION WASHER
NUT

Figure 23. Eyelet Mounting

Figure 26. Screw−Mounted Isolated Package

CLIP

Figure 24. Clips
HEATSINK

Figure 27. Clip−Mounted Isolated Package
MOUNTING ARRANGEMENTS FOR THE ISOLATEDPACKAGE AS COMPARED TO A CONVENTIONAL

RECOMMENDED MOUNTING ARRANGEMENTS FOR
TO−225AA (TO−126) THERMOPAD PACKAGES

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15

AN1040/D

CASE 369−07

resistance and reduce thermal resistance. As a generalpractice, however, it is better to support the package. A
plastic support for the TO−220 Package and other similartypes is offered by heatsink accessory vendors.
In many situations, because its leads are fairly heavy, theCase 77 (TO−225AA) (TO−127) package has supported asmall heatsink; however, no definitive data is available.
When using a small heatsink, it is good practice to have thesink rigidly mounted such that the sink or the board isproviding total support for the semiconductor. Two
possible arrangements are shown in Figure 30 and
Figure 31. The arrangement of Figure 30 could be usedwith any plastic package, but the scheme of Figure 31 ismore practical with Case 77 Thermopad devices. With theother package types, mounting the transistor on top of theheatsink is more practical.

CASE 369A−13

Figure 28. Surface Mount D−PAK Parts

Standard Glass−Epoxy 2−ounce boards do not make very
good heatsinks because the thin foil has a high thermal
resistance. As Figure 29 shows, thermal resistanceasymptotes to about 20°C/W at 10 square inches of board
area, although a point of diminishing returns occurs at
about 3 square inches.
Boards are offered that have thick aluminum or copper
substrates. A dielectric coating designed for low thermal
resistance is overlaid with one− or two−ounce copper foil
for the preparation of printed conductor traces. Tests run onsuch a product indicate that case to substrate thermal
resistance is in the vicinity of 1°C/W, exact values
depending upon board type.(7) The substrate may be aneffective heatsink itself, or it can be attached to aconventional finned heatsink for improved performance.
Since DPAK and other surface mount packages aredesigned to be compatible with surface mount assembly
techniques, no special precautions are needed other than toinsure that maximum temperature/time profiles are notexceeded.

HEATSINK

TO−225AA
CASE 77
HEATSINK
SURFACER θ AJ, THERMAL RESISTANCE ( C/W)

CIRCUIT BOARD
100°

Figure 30. Simple Plate, Vertically Mounted

PCB, 1/16 IN THICK
G10/FR4, 2 OUNCEEPOXY GLASS BOARD,DOUBLE SIDED

80

60

TWIST LOCKSORSOLDERABLELEGSHEATSINK

40

20
TO−225AA
CASE 77
HEATSINK
SURFACECIRCUIT
BOARD

0
2

4
6
PCB PAD AREA (IN2)810Figure 29. Effect of Footprint Area on Thermal
Resistance of DPAK Mounted on a Glass−Epoxy Board

FREE AIR AND SOCKET MOUNTING
In applications where average power dissipation is on theorder of a watt or so, most power semiconductors may be
mounted with little or no heatsinking. The leads of thevarious metal power packages are not designed to support
the packages; their cases must be firmly supported to avoid
the possibility of cracked seals around the leads. Many
plastic packages may be supported by their leads inapplications where high shock and vibration stresses are
not encountered and where no heatsink is used. The leads
should be as short as possible to increase vibration

Figure 31. Commercial Sink, Horizontally Mounted
METHODS OF USING SMALL HEATSINKS WITH
PLASTIC SEMICONDUCTOR PACKAGES

In certain situations, in particular where semiconductor
testing is required or prototypes are being developed,

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AN1040/D

CONNECTING AND HANDLING TERMINALS
Pins, leads, and tabs must be handled and connected
properly to avoid undue mechanical stress which could
cause semiconductor failure. Change in mechanicaldimensions, as a result of thermal cycling over operating
temperature extremes, must be considered. Standard metal,
plastic, and RF stripline packages each have some special
considerations.

greater than 4 pounds may result in permanent damage tothe device. If the mounting arrangement imposes axial
stress on the leads, a condition which may be caused bythermal cycling, some method of strain relief should be
devised. When wires are used for connections, care should
be exercised to assure that movement of the wire does notcause movement of the lead at the lead−to−plastic
junctions. Highly flexible or braided wires are good forproviding strain relief.
Wire−wrapping of the leads is permissible, provided thatthe lead is restrained between the plastic case and the pointof the wrapping. The leads may be soldered; the maximum
soldering temperature, however, must not exceed 260°C
and must be applied for not more than 5 seconds at a
distance greater than 1/8 inch from the plastic case.

Metal Packages

Stripline Packages

The pins and lugs of metal packaged devices using glass
to metal seals are not designed to handle any significant
bending or stress. If abused, the seals could crack. Wires
may be attached using sockets, crimp connectors or solder,provided the data sheet ratings are observed. When wires
are attached directly to the pins, flexible or braided leads
are recommended in order to provide strain relief.

The leads of stripline packages normally are soldered
into a board while the case is recessed to contact a heatsink
as shown in Figure 32 through Figure 34. The following
rules should be observed:
1. The device should never be mounted in such a manneras to place ceramic−to−metal joints in tension.
2. The device should never be mounted in such a manneras to apply force on the strip leads in a verticaldirection towards the cap.
3. When the device is mounted in a printed circuit board
with the copper stud and BeO portion of the header
passing through a hole in the circuit boards, adequate
clearance must be provided for the BeO to prevent
shear forces from being applied to the leads.
4. Some clearance must be allowed between the leads andthe circuit board when the device is secured to theheatsink.
5. The device should be properly secured into theheatsinks before its leads are attached into the circuit.
6. The leads on stud type devices must not be used toprevent device rotation during stud torque application.
A wrench flat is provided for this purpose.
Figure 33 shows a cross−section of a printed circuitboard and heatsink assembly for mounting a stud−typestripline device. H is the distance from the top surface ofthe printed circuit board to the D−flat heatsink surface. If H
is less than the minimum distance from the bottom of thelead material to the mounting surface of the package, there
is no possibility of tensile forces in the copper stud − BeO
ceramic joint. If, however, H is greater than the package
dimension, considerable force is applied to the cap to BeO
joint and the BeO to stud joint. Two occurrences are
possible at this point. The first is a cap joint failure when
the structure is heated, as might occur during thelead−soldering operation; while the second is BeO to studfailure if the force generated is high enough. Lack ofcontact between the device and the heatsink surface will
occur as the differences between H and the package

sockets are desirable. Manufacturers have provided sockets
for many of the packages available from onsemi. The user
is urged to consult manufacturers’ catalogs for specificdetails. Sockets with Kelvin connections are necessary toobtain accurate voltage readings across semiconductor
terminals.

EMS Modules

The screw terminals of the EMS modules look
deceptively rugged. Since the flange base is mounted to arigid heatsink, the connection to the terminals must allow
some flexibility. A rigid buss bar should not be bolted toterminals. Lugs with braid are preferred.
Plastic Packages

The leads of the plastic packages are somewhat flexible
and can be reshaped, although this is not a recommended
procedure. In many cases, a heatsink can be chosen whichmakes lead−bending unnecessary. Numerous lead andtab−forming options are available from onsemi on large
quantity orders. Preformed leads remove the users’ risk ofdevice damage caused by bending.
If, however, lead−bending is done by the user, several
basic considerations should be observed. When bending
the lead, support must be placed between the point ofbending and the package. For forming small quantities ofunits, a pair of pliers may be used to clamp the leads at thecase, while bending with the fingers or another pair ofpliers. For production quantities, a suitable fixture should
be made.
The following rules should be observed to avoid damage
to the package.
1. A leadbend radius greater than 1/16 inch is advisablefor TO−225AA (CASE 77) and 1/32 inch for TO−220.
2. No twisting of leads should be done at the case.
3. No axial motion of the lead should be allowed withrespect to the case.
The leads of plastic packages are not designed towithstand excessive axial pull. Force in this direction

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AN1040/D
dimension become larger; this may result in device failure
as power is applied.

the package are avoided. However, if distance H exceeds
the package dimension, problems similar to those
discussed for the stud type devices can occur.
CLEANING CIRCUIT BOARDS
It is important that any solvents or cleaning chemicals
used in the process of degreasing or flux removal do notaffect the reliability of the devices. Alcohol andunchlorinated Freon solvents are generally satisfactory for
use with plastic devices, since they do not damage thepackage. Hydrocarbons such as gasoline and chlorinatedFreon may cause the encapsulant to swell, possibly
damaging the transistor die.
When using an ultrasonic cleaner for cleaning circuitboards, care should be taken with regard to ultrasonicenergy and time of application. This is particularly true if
any packages are free−standing without support.

CERAMICCAP

TRANSISTOR
CHIP

LEADS

METALLICPATTERNBeO
DISC
WRENCHFLAT

SURFACE S

Figure 32. Component Parts of a Stud Mount
Stripline Package. Flange Mounted
Packages are Similarly Constructed

THERMAL SYSTEM EVALUATION
Assuming that a suitable method of mounting thesemiconductor without incurring damage has beenachieved, it is important to ascertain whether the junction
temperature is within bounds.
In applications where the power dissipated in thesemiconductor consists of pulses at a low duty cycle, theinstantaneous or peak junction temperature, not averagetemperature, may be the limiting condition. In this case,use must be made of transient thermal resistance data. For afull explanation of its use, see onsemi Application Note,
AN569/D.
Other applications, notably RF power amplifiers or
switches driving highly reactive loads, may create severe
current crowding conditions which render the traditional
concepts of thermal resistance or transient thermal
impedance invalid. In this case, transistor safe operating
area, thyristor di/dt limits, or equivalent ratings asapplicable, must be observed.
Fortunately, in many applications, a calculation of theaverage junction temperature is sufficient. It is based on theconcept of thermal resistance between the junction and atemperature reference point on the case. (See Appendix A.)
A fine wire thermocouple should be used, such as #36
AWG, to determine case temperature. Average operating
junction temperature can be computed from the following
equation:“D” FLATPRINTEDCIRCUIT
BOARD
HEAT
SINK
SURFACE“D” FLATTOP
VIEW

PRINTEDCONDUCTORPATTERN

SIDE VIEW
CROSS SECTION

METAL
HEAT
SINK

Figure 33. Typical Stud Type SOE Transistor
Mounting Method
MOUNTING
HOLES
METAL
HEATSINK
SURFACECIRCUITBOARD

TOP VIEW

COPPERCONDUCTORSALIGNMENTSPACERMETAL HEATSINK SURFACESIDE VIEW
CROSS SECTION

TJ = TC + RθJC x PD

where

Figure 34. Flange Type SOE Transistor Mounting
MethodMOUNTING DETAILS FOR SOE TRANSISTORS

Figure 34 shows a typical mounting technique forflange−type stripline transistors. Again, H is defined as the
distance from the top of the printed circuit board to theheatsink surface. If distance H is less than the minimum
distance from the bottom of transistor lead to the bottom
surface of the flange, tensile forces at the various joints in

TJ= junction temperature (°C)
TC
= case temperature (°C)
RθJC = thermal resistance junction−to case as
specified on the data sheet (°C/W)
PD= power dissipated in the device (W)The difficulty in applying the equation often lies indetermining the power dissipation. Two commonly used
empirical methods are graphical integration andsubstitution.

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18

AN1040/D
Graphical Integration

switching arrangement is provided which allows operating
the load with the device under test, until it stabilizes intemperature. Case temperature is monitored. By throwing
the switch to the “test” position, the device under test isconnected to a dc power supply, while another pole of theswitch supplies the normal power to the load to keep it
operating at full power level. The dc supply is adjusted sothat the semiconductor case temperature remains
approximately constant when the switch is thrown to eachposition for about 10 seconds. The dc voltage and current
values are multiplied together to obtain average power. It is
generally necessary that a Kelvin connection be used forthe device voltage measurement.

Graphical integration may be performed by taking
oscilloscope pictures of a complete cycle of the voltage andcurrent waveforms, using a limit device. The pictures
should be taken with the temperature stabilized.
Corresponding points are then read from each photo at asuitable number of time increments. Each pair of voltage
and current values are multiplied together to give
instantaneous values of power. The results are plotted onlinear graph paper, the number of squares within the curvecounted, and the total divided by the number of squares
along the time axis. The quotient is the average power
dissipation. Oscilloscopes are available to perform thesemeasurements and make the necessary calculations.
Substitution

This method is based upon substituting an easily
measurable, smooth dc source for a complex waveform. A

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19

AN1040/D
APPENDIX A
THERMAL RESISTANCE CONCEPTS
The basic equation for heat transfer under steady−state
conditions is generally written as:

PD = power dissipation
RθJC = semiconductor thermal resistance(junction to case),
RθCS = interface thermal resistance (case toheat−sink),
RθSA = heat sink thermal resistance (heatsink
to ambient),TA= ambient temperature.
The thermal resistance junction to ambient is the sum of
the individual components. Each component must be
minimized if the lowest junction temperature is to result.
The value for the interface thermal resistance, RθCS, may
be significant compared to the other thermal resistanceterms. A proper mounting procedure can minimize RθCS.
The thermal resistance of the heatsink is not absolutely
constant; its thermal efficiency increases as ambient
temperature increases and it is also affected by orientationof the sink. The thermal resistance of the semiconductor isalso variable; it is a function of biasing and temperature.
Semiconductor thermal resistance specifications arenormally at conditions where current density is fairly
uniform. In some applications, such as in RF power
amplifiers and short−pulse applications, current density is
not uniform and localized heating in the semiconductor
chip will be the controlling factor in determining power
handling ability.

q = hAΔT (1)

where

q

= rate of heat transfer or power
dissipation (PD)h= heat transfer coefficient,A= area involved in heat transfer,
ΔT = temperature difference between
regions of heat transfer.
However, electrical engineers generally find it easier towork in terms of thermal resistance, defined as the ratio of
temperature to power. From Equation 1, thermal resistance,Rθ, isRθ = ΔT/q = 1/hA (2)The coefficient (h) depends upon the heat transfer
mechanism used and various factors involved in thatparticular mechanism.
An analogy between Equation (2) and Ohm’s Law isoften made to form models of heat flow. Note that T could
be thought of as a voltage thermal resistance corresponds toelectrical resistance (R); and, power (q) is analogous tocurrent (I). This gives rise to a basic thermal resistancemodel for a semiconductor as indicated by Figure 35.
The equivalent electrical circuit may be analyzed byusing Kirchoff’s Law and the following equation results:
where

TJ = PD (RθJC + PθCS + RθSA) + TA (3)TJ= junction temperature,

TJ, JUNCTION TEMPERATURE
DIE
INSULATORSTC, CASE TEMPERATURE
TS, HEATSINKTEMPERATUREHEATSINK

TA, AMBIENTTEMPERATURE

FLAT WASHER

RθJC

PD

RθCS
RθSA

SOLDER TERMINAL
NUT

REFERENCE TEMPERATURE

Figure 35. Basic Thermal Resistance Model Showing Thermal to Electrical Analogy for a Semiconductor

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20

AN1040/D
APPENDIX B
MEASUREMENT OF INTERFACE THERMAL RESISTANCE
2. The JEDEC location is close to the die on the top
surface of the package base reached through a blindhole drilled through the molded body. The
thermocouple is swaged in place.
3. The Thermalloy location is on the top portion of thetab between the molded body and the mounting screw.
The thermocouple is soldered into position.

Measuring the interface thermal resistance RθCS appears
deceptively simple. All that’s apparently needed is athermocouple on the semiconductor case, a thermocouple
on the heatsink, and a means of applying and measuring
DC power. However, RθCS is proportional to the amount ofcontact area between the surfaces and consequently isaffected by surface flatness and finish and the amount ofpressure on the surfaces. The fastening method may also bea factor. In addition, placement of the thermocouples canhave a significant influence upon the results. Consequently,
values for interface thermal resistance presented bydifferent manufacturers are not in good agreement.
Fastening methods and thermocouple locations are
considered in this Appendix.
When fastening the test package in place with screws,
thermal conduction may take place through the screws, forexample, from the flange ear on a TO−3 package directly tothe heatsink. This shunt path yields values which are
artificially low for the insulation material and dependent
upon screw head contact area and screw material.
MIL−I−49456 allows screws to be used in tests forinterface thermal resistance probably because it can beargued that this is “application oriented.”
Thermalloy takes pains to insulate all possible shuntconduction paths in order to more accurately evaluate
insulation materials. The onsemi fixture uses an insulated
clamp arrangement to secure the package which also does
not provide a conduction path.
As described previously, some packages, such as a
TO−220, may be mounted with either a screw through thetab or a clip bearing on the plastic body. These two
methods often yield different values for interface thermal
resistance. Another discrepancy can occur if the top of the
package is exposed to the ambient air where radiation andconvection can take place. To avoid this, the package
should be covered with insulating foam. It has been
estimated that a 15 to 20% error in RθCS can be incurredfrom this source.
Anothersignificant
cause
for
measurement
discrepancies is the placement of the thermocouple tomeasure the semiconductor case temperature. Consider the
TO−220 package shown in 36. The mounting pressure at
one end causes the other end − where the die is located − tolift off the mounting surface slightly. To improve contact,
onsemi TO−220 Packages are slightly concave. Use of a
spreader bar under the screw lessens the lifting, but some isinevitable with a package of this structure. Threethermocouple locations are shown:
1. The onsemi location is directly under the die reachedthrough a hole in the heatsink. The thermocouple isheld in place by a spring which forces thethermocouple into intimate contact with the bottom of
the semi’s case.

DIE

E.I.A.

THERMALLOY

onsemiFigure 36. JEDEC TO−220 Package Mounted to
Heatsink Showing Various Thermocouple Locationsand Lifting Caused by Pressure at One End

Temperatures at the three locations are generally not thesame. Consider the situation depicted in the figure.
Because the only area of direct contact is around themounting screw, nearly all the heat travels horizontally
along the tab from the die to the contact area.
Consequently, the temperature at the JEDEC location ishotter than at the Thermalloy location and the onsemi
location is even hotter. Since junction−to−sink thermal
resistance must be constant for a given test setup, thecalculated junction−to−case thermal resistance values
decrease and case−to−sink values increase as the “case”
temperature thermocouple readings become warmer. Thus,
the choice of reference point for the “case” temperature isquite important.
There are examples where the relationship between thethermocouple temperatures are different from the previous
situation. If a mica washer with grease is installed between
the semiconductor package and the heatsink, tightening thescrew will not bow the package; instead, the mica will be
deformed. The primary heat conduction path is from thedie through the mica to the heatsink. In this case, a small
temperature drop will exist across the vertical dimension of
the package mounting base so that the thermocouple at the
EIA location will be the hottest. The thermocouple
temperature at the Thermalloy location will be lower, butclose to the temperature at the EIA location as the lateralheat flow is generally small. The onsemi location will becoolest.
The EIA location is chosen to obtain the highest
temperature on the case. It is of significance because power

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21

AN1040/D
semiconductors becoming available, however, thedifference becomes significant and it is important that thesemiconductor manufacturer and equipment manufacturer
use the same reference point.
Another EIA method of establishing reference
temperatures utilizes a soft copper washer (thermal greaseis used) between the semiconductor package and theheatsink. The washer is flat to within 1 mil/inch, has afinish better than 63 μ−inch, and has an imbedded
thermocouple near its center. This reference includes theinterface resistance under nearly ideal conditions and is,therefore, application−oriented. It is also easy to use, but
has not become widely accepted.
A good way to improve confidence in the choice of casereference point is to also test for junction−to−case thermal
resistance while testing for interface thermal resistance. If
the junction−to−case values remain relatively constant asinsulators are changed, torque varied, etc., then the casereference point is satisfactory.

ratings are supposed to be based on this reference point.
Unfortunately, the placement of the thermocouple istedious and leaves the semiconductor in a condition unfit
for sale.
The onsemi location is chosen to obtain the highest
temperature of the case at a point where, hopefully, the caseis making contact to the heatsink. Once the special
heatsink, to accommodate the thermocouple has been
fabricated, this method lends itself to production testingand does not mark the device. However, this location is noteasily accessible to the user.
The Thermalloy location is convenient and is oftenchosen by equipment manufacturers. However, it also
blemishes the case and may yield results differing up to
1°C/W for a TO−220 package mounted to a heatsink
without thermal grease and no insulator. This error is small
when compared to the thermal resistance of heat dissipaters
often used with this package, since power dissipation isusually a few watts. When compared to the specified
junction−to−case values of some of the higher power

APPENDIX C
Sources of Accessories
Insulators
Joint
CompoundAdhesives

BeO

AlO2

Anodize

Mica

Plastic
Film

Silicone
RubberHeatsinks

Clips

Aavid

−

−

−

−

−

−

X

X

X

X

AHAM−TOR

−

−

−

−

−

−

−

−

X

−

Asheville−
Schoonmaker

−

−

−

−

−

X

−

−

−

−

Astrodynamis

X

−

−

−

−

−

−

−

X

−

Delbert Blinn

−

−

X

−

X

X

X

X

X

−

IERC

X

−

−

−

−

−

−

−

X

−

Staver

−

−

−

−

−

−

−

−

X

−

Thermalloy

X

X

X

X

X

X

X

X

X

X

Tran−tec

X

−

X

X

X

X

−

X

X

−

Wakefield

X

X

X

−

X

−

−

X

X

X

Manufacturer

Other Sources for silicone rubber pads: Chomerics, Bergquist

Suppliers Addresses
Aavid Engineering, Inc., P.O. Box 400, Laconia, New Hampshire 03247(603) 524−1478
AHAM−TOR Heatsinks, 27901 Front Street, Rancho, California 92390(714) 676−4151
Asheville−Schoonmaker, 900 Jefferson Ave., Newport News, VA 23607(804) 244−7311
Astro Dynamics, Inc., 2 Gill St., Woburn, Massachusetts 01801(617) 935−4944
Bergquist, 5300 Edina Industrial Blvd., Minneapolis, Minnesota 55435(612) 835−2322
Chomerics, Inc.,16 Flagstone Drive, Hudson, New Hampshire 03051
1−800−633−8800
Delbert Blinn Company, P.O. Box 2007, Pomona, California 91769(714) 623−1257
International Electronic Research Corporation, 135 West Magnolia Boulevard, Burbank, California 91502(213) 849−2481
The Staver Company, Inc., 41−51 Saxon Avenue, Bay Shore, Long Island, New York 11706(516) 666−8000
Thermalloy, Inc., P.O. Box 34829, 2021 West Valley View Lane, Dallas, Texas 75234(214) 243−4321
Tran−tec Corporation, P.O. Box 1044, Columbus, Nebraska 68601(402) 564−2748
Wakefield Engineering, Inc., Wakefield, Massachusetts 01880(617) 245−5900

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22

AN1040/D
PACKAGE INDEXPREFACE
When the JEDEC registration system for package
outlines started in 1957, numbers were assigned
sequentially whenever manufacturers wished to establish apackage as an industry standard. As minor variations
developed from these industry standards, either a new,non−related number was issued by JEDEC ormanufacturers would attempt to relate the part to anindustry standard via some appended description.
In an attempt to ease confusion, JEDEC established thepresent system in late 1968 in which new packages are
assigned into a category, based on their general physicalappearance. Differences between specific packages in a

ON
Case
Number
001
003
009
011
011A
012
036
042A
044
054
056
058
61-04
63-02
63-03
077
080
086
086L
144B-05
145A-09
145A-10145C
157
160-03167
174-04

JEDEC Outline
Original
System

Revised
SystemMounting
Notes Class

TO-3
TO-3
TO-61
TO-3
TO-3
TO-3
TO-60
DO-5
DO-4
TO-3
DO-4
DO-5

TO-204AA

TO-64
TO-64
TO-126
TO-66−−

TO-208AB
TO-2088AB
TO-225AA
TO-213AA
TO-208TO-298−−1
1

TO-232−
TO-59−

DO-203
TO-210AA
DO-2031
1−
1

2
TO-210AC
TO-204AA−−
TO-210AB
DO-203AB
DO-203AA
−
−
−

−
2
2
−
−
−
2
−
2

FlangeFlangeStud
FlangeFlangeFlange
Stud
Stud
Stud
FlangeStud
Stud
FlangeStud
Stud
Plastic
Flange
Stud
Stud
Stud
Stud
Stud
Stud
Stud
Stud
Stud
Pressfit

ON
Case
Number175-03
197
211-07211-11215-02
221
221C-02
221D-02235
235-03238
239
244-04245
257-01
263
263-04283
289
305-01
310-02311-02311-02311-02314B-03category are denoted by suffix letters. The older package
designations were re−registered to the new system as time
permitted.
For example the venerable TO−3 has many variations.
Can heights differ and it is available with 30, 40, 50, and 60
mil pins, with and without lugs. It is now classified in the
TO−204 family. The TO−204AA conforms to the original
outline for the TO−3 having 40 mil pins while theTO−204AE has 60 mil pins, for example.
The new numbers for the old parts really haven’t caught
on very well. It seems that the DO−4, DO−5 and TO−3 still
convey sufficient meaning for general verbal
communication.

JEDEC Outline
Original
System

Revised
SystemMounting
Class
Notes

−

TO-204AE−−

TO-220AB

−

−

−

−

TO-208−−

TO-208
TO-208

DO-4
DO-5
−

−
−
TO-208

DO-4−−
TO-209IsolatedTO-2201

Stud
FlangeFlangeFlangeFlangeTab
Plastic
Plastic

Stud
Stud
Stud
1
Stud
−
Stud
Stud
−
Stud
−
Stud
−
Stud
Stud
−
Stud
1
Stud
Pressfit
Isolated Stud
Pressfit
Stud
Tab

ON
Case
NumberJEDEC Outline
Original
System

314D-03316-01319-06
328A-03332-04333-04333A-02336-03337-02340
340A-02
340B-03342-01
357B-01
361-01368-02369-06
369A-12373-01
383-01387-01
388A-01744-02
744A-01
043-07

Revised
SystemNotes

TO-218AC
IsolatedTO-218

DO-21

Mounting
Class
Tab
FlangeFlangeFlangeStud
FlangeFlangeFlangeFlangeTab
Plastic
Plastic

FlangeFlangeFlangeFlangeInsertion
TO-251
SurfaceTO-252Isolated Flange
Isolated Flange
TO-254AA Isolated 2 Tab
TO-258AA Isolated 2 Tab
FlangeFlangePressfit
DO-208AA

Notes: 1. Would fit within this family outline if registered with JEDEC.
2. Not within all JEDEC dimensions.

(6) Catalog, Edition 18, Richco Plastic Company, 5825 N. Tripp
Ave., Chicago, IL 60546.
(7) Herb Fick, “Thermal Management of Surface Mount Power
Devices,” Powerconversion and Intelligent Motion, August
1987.

(1) MIL−HANDBOOK − 2178, SECTION 2.2.
(2) “Navy Power Supply Reliability − Design and Manufacturing
Guidelines” NAVMAT P4855−1, Dec. 1982 NAVPUBFORCEN,
5801 Tabor Ave., Philadelphia, PA 19120.
(3) Catalog #87−HS−9, (1987), page 8, Thermalloy, Inc., P.O. Box
810839, Dallas, Texas 75381−0839.
(4) ITW Shakeproof, St. Charles Road, Elgin, IL 60120.
(5) Robert Batson, Elliot Fraunglass and James P Moran, “HeatDissipation Through Thermalloy Conductive Adhesives,”
EMTAS ’83. Conference, February 1 − 3, Phoenix, AZ; Societyof Manufacturing Engineers, One SME Drive, P.O. Box 930,
Dearborn, Ml 48128.

www.onsemi.com
23

AN1040/D

Grafoil is a registered Union Carbide.
Kon−Dux and Rubber−Duc are trademarks of Aavid Thermal Technologies, Inc.
Thermasil is a registered trademark and Thermafilm is a trademark of Thermalloy, Inc.
Kapton is a registered trademark of du Pont de Nemours & Co., Inc.
Sil−Pad is a registered trademark of the Bergquist Company.
CHO−THERM is a registered trademark of Chomerics, Inc.
FULLPAK, ICePAK and Thermopad are trademarks of Semiconductor Componenets Industries, LLC.
onsemi,, and other names, marks, and brands are registered and/or common law trademarks of Semiconductor Components Industries, LLC dba “onsemi” or its affiliates
and/or subsidiaries in the United States and/or other countries. onsemi owns the rights to a number of patents, trademarks, copyrights, trade secrets, and other intellectual property.
A listing of onsemi’s product/patent coverage may be accessed at www.onsemi.com/site/pdf/Patent−Marking.pdf. onsemi reserves the right to make changes at any time to any
products or information herein, without notice. The information herein is provided “as−is” and onsemi makes no warranty, representation or guarantee regarding the accuracy of theinformation, product features, availability, functionality, or suitability of its products for any particular purpose, nor does onsemi assume any liability arising out of the application or useof any product or circuit, and specifically disclaims any and all liability, including without limitation special, consequential or incidental damages. Buyer is responsible for its products
and applications using onsemi products, including compliance with all laws, regulations and safety requirements or standards, regardless of any support or applications information
provided by onsemi. “Typical” parameters which may be provided in onsemi data sheets and/or specifications can and do vary in different applications and actual performance mayvary over time. All operating parameters, including “Typicals” must be validated for each customer application by customer’s technical experts. onsemi does not convey any licenseunder any of its intellectual property rights nor the rights of others. onsemi products are not designed, intended, or authorized for use as a critical component in life support systems
or any FDA Class 3 medical devices or medical devices with a same or similar classification in a foreign jurisdiction or any devices intended for implantation in the human body. Should
Buyer purchase or use onsemi products for any such unintended or unauthorized application, Buyer shall indemnify and hold onsemi and its officers, employees, subsidiaries, affiliates,and distributors harmless against all claims, costs, damages, and expenses, and reasonable attorney fees arising out of, directly or indirectly, any claim of personal injury or deathassociated with such unintended or unauthorized use, even if such claim alleges that onsemi was negligent regarding the design or manufacture of the part. onsemi is an Equal
Opportunity/Affirmative Action Employer. This literature is subject to all applicable copyright laws and is not for resale in any manner.

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Phone: 011 421 33 790 2910

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