®
APPLICATION BULLETIN
Mailing Address: PO Box 11400 • Tucson, AZ 85734 • Street Address: 6730 S. Tucson Blvd. • Tucson, AZ 85706
Tel: (602) 746-1111 • Twx: 910-952-111 • Telex: 066-6491 • FAX (602) 889-1510 • Immediate Product Info: (800) 548-6132
MOUNTING CONSIDERATIONS FOR TO-3 PACKAGES
By Hubert Biagi (602) 746-7422
Proper mounting of TO-3 packages is required to assure rated
performance and reliability. Although the procedures are
simple, ignoring them can result in poor performance and
catastrophic failure of the device.
PACKAGE HANDLING
The TO-3 package is a rugged hermetic package, but it can be
damaged with improper handling. Excessive bending or twist-
ing of the package pins can crack the glass seal around the pin
and result in loss of hermeticity. If pin straightening is
required, clamp the pin against the package base using needle-
nose pliers. This will strain-relieve the pin during the straight-
ening operation.
Another potential problem is cracking the internal circuit
substrate from bending of the package base. This can be
caused by mounting the package onto a non-flat surface,
improper use of a compressible thermal pad, or over-tighten-
ing the mounting fasteners.
TO-3 SOCKET
The Burr-Brown 0804MC TO-3 socket is designed to meet
the requirements of high current, high power products such as
the OPA512, OPA541, and OPA2541. The socket has a
rugged contact design which assures positive and reliable
contact even when using thermal grease and pre-tinned pins.
The closed-ended contacts will accept the full pin length of the
TO-3 and guard against solder and flux contamination. The
socket body has a center hole which allows for direct measure-
ment of TO-3 case temperature.
FASTENERS
The fastener hardware used to mount the TO-3 package is very
important. Table I describes the proper hardware combina-
tion. Sources for fastener hardware are listed at the end of this
bulletin. The preferred fastener material is stainless steel.
Plated steel is a good alternative. Brass or plastic fasteners are
not recommended.
The mounting holes of the TO-3 package are designed to
accept 6-32 machine screws; no other size should be used (see
exploded views in Figure 1A and 1B). The pan-head is the best
head style. It has a low profile and large bearing face to
properly cover the mounting hole, but its not so large as to ride
up onto the lip of the welded cover.
In order to maintain proper mounting pressure, the Belleville
spring washer (also known as a conical compression washer),
is recommended. Split ring and star lock washers are not
recommended. They typically bottom out at less than 50
pounds, whereas 150-300 pounds of pressure is needed to
TO-3 Package
6-32 Pan Head
Mounting Joint
Teflon Sleeves
0.250" Max
Heat Sink
0804MC Socket
Belleville Washer
No. 6N Washers
5/16 Full Nut
or
5/16 Locknut
FIGURE 1A. High Power Application Using 0804MC Socket.
©
1992 Burr-Brown Corporation
AB-037
Printed in U.S.A. March, 1992
ETC [ ETC ]
