BUL44 BUL44F

8

Motorola Bipolar Power Transistor Device Data

TEST CONDITIONS FOR ISOLATION TESTS*

MOUNTED

FULLY ISOLATED

PACKAGE

LEADS

HEATSINK

0.110

″ MIN

Figure 22a. Screw or Clip Mounting Position

for Isolation Test Number 1

* Measurement made between leads and heatsink with all leads shorted together.

CLIP

MOUNTED

FULLY ISOLATED

PACKAGE

LEADS

HEATSINK

CLIP

0.107

″ MIN

MOUNTED

FULLY ISOLATED

PACKAGE

LEADS

HEATSINK

0.107

″ MIN

Figure 22b. Clip Mounting Position

for Isolation Test Number 2

Figure 22c. Screw Mounting Position

for Isolation Test Number 3

MOUNTING INFORMATION**

4–40 SCREW

PLAIN WASHER

HEATSINK

COMPRESSION WASHER

NUT

CLIP

HEATSINK

Laboratory tests on a limited number of samples indicate, when using the screw and compression washer mounting technique, a screw

torque of 6 to 8 in . lbs is sufficient to provide maximum power dissipation capability. The compression washer helps to maintain a constant

pressure on the package over time and during large temperature excursions.

Destructive laboratory tests show that using a hex head 4–40 screw, without washers, and applying a torque in excess of 20 in . lbs will

cause the plastic to crack around the mounting hole, resulting in a loss of isolation capability.

Additional tests on slotted 4–40 screws indicate that the screw slot fails between 15 to 20 in . lbs without adversely affecting the package.

However, in order to positively ensure the package integrity of the fully isolated device, Motorola does not recommend exceeding 10 in . lbs

of mounting torque under any mounting conditions.

Figure 23a. Screw–Mounted

Figure 23b. Clip–Mounted

Figure 23. Typical Mounting Techniques

for Isolated Package

** For more information about mounting power semiconductors see Application Note AN1040.