AC08FSM datasheet(145/223 Pages) TECCOR

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Application Notes

AN1004

AN1004 - 3

http://www.teccor.com

Thyristor Product Catalog

+1 972-580-7777

Allow for adequate ventilation. If possible, route heat sinks to out-

side of assembly for maximum airflow.

Mounting Surface Selection

Proper mounting surface selection is essential to efficient trans-

fer of heat from the semiconductor device to the heat sink and

from the heat sink to the ambient. The most popular heat sinks

are flat aluminum plates or finned extruded aluminum heat sinks.

The mounting surface should be clean and free from burrs or

scratches. It should be flat within 0.002 inch per inch, and a sur-

face finish of 30 to 60 microinches is acceptable. Surfaces with a

higher degree of polish do not produce better thermal conductiv-

ity.

Many aluminum heat sinks are black anodized to improve ther-

mal emissivity and prevent corrosion. Anodizing results in high

electrical but negligible thermal insulation. This is an excellent

choice for isolated TO-220 devices. For applications of TO-202

devices where electrical connection to the common anode tab is

required, the anodization should be removed. Iridite or chromate

acid dip finish offers low electrical and thermal resistance. Either

TO-202 or isolated TO-220 devices may be mounted directly to

this surface, regardless of application. Both finishes should be

cleaned prior to use to remove manufacturing oils and films.

Some of the more economical heat sinks are painted black. Due

to the high thermal resistance of paint, the paint should be

removed in the area where the semiconductor is attached.

Bare aluminum should be buffed with #000 steel wool and fol-

lowed with an acetone or alcohol rinse. Immediately, thermal

grease should be applied to the surface and the device mounted

down to prevent dust or metal particles from lodging in the critical

interface area.

For good thermal contact, the use of thermal grease is essential

to fill the air pockets between the semiconductor and the mount-

ing surface. This decreases the thermal resistance by 20%. For

example, a typical TO-220 with RθJC of 1.2 °C/W may be lowered

to 1 °C/W by using thermal grease.

Teccor recommends Dow-Corning 340 as a proven effective ther-

mal grease. Fibrous applicators are not recommended as they

may tend to leave lint or dust in the interface area. Ensure that

the grease is spread adequately across the device mounting sur-

face, and torque down the device to specification.

Contact Teccor Applications Engineering for assistance in choos-

ing and using the proper heat sink for specific application.

Hardware And Methods

TO-220

The mounting hole for the Teccor TO-220 devices should not

exceed 0.140” (6/32) clearance. (Figure AN1004.7) No insulating

bushings are needed for the L Package (isolated) devices as the

tab is electrically isolated from the semiconductor chip. 6/32

mounting hardware, especially round head or Fillister machine

screws, is recommended and should be torqued to a value of

6 inch-lbs.

Figure AN1004.7

TO-220 Mounting

Punched holes are not acceptable due to cratering around the

hole which can cause the device to be pulled into the crater by

the fastener or can leave a significant portion of the device out of

contact with the heat sink. The first effect may cause immediate

damage to the package and early failure, while the second can

create higher operating temperatures which will shorten operat-

ing life. Punched holes are quite acceptable in thin metal plates

where fine-edge blanking or sheared-through holes are

employed.

Drilled holes must have a properly prepared surface. Excessive

chamfering is not acceptable as it may create a crater effect.

Edges must be deburred to promote good contact and avoid

puncturing isolation materials.

For high-voltage applications, it is recommended that only the

metal portion of the TO-220 package (as viewed from the bottom

of the package) be in contact with the heat sink. This will provide

maximum oversurface distance and prevent a high voltage path

over the plastic case to a grounded heat sink.

TO-202

The mounting hole for the Teccor TO-202 devices should not

exceed 0.112” (4/40) clearance. (Figure AN1004.8) Since tab is

electrically common with anode, heat sink may or may not need

to be electrically isolated from tab. If not, use 4/40 screw with

lock washer and nut. Mounting torque is 6 inch-lbs.

Figure AN1004.8

TO-202 Mounting

A nylon bushing and mica insulation are required to insulate the

tab in an isolated application. A compression washer is recom-

mended to avoid damage to the bushing. Do not attempt to

mount non-formed tabs to a plane surface, as the resulting strain

on the case may cause it or the semiconductor chip assembly to

fail. Teccor has the facilities and expertise to properly tab form

TO-202 devices for the convenience of the consumer.

Lockwasher

6-32 Nut

Heatsink

* Mounting

screw

6-32

* Screw head must not touch

the epoxy body of the device

oid

axial

stress

Boundar

y of

exposed

metal tab

On heavy aluminum heatsinks

High potential appication

using Isolated TO-220

Heat Sink

at Case

Potential

Heat Sink

Compression

Washer

Nut

Appropriate

Screw

4/40 Nylon

Bushing

Mica

Insulator

Tab

Form

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