Package attachment to core by means of boltdown method

AN3232

18/26

Doc ID 17594 Rev 3

Figure 8.

First boltdown mounting steps

To further improve the distribution of pressure from the screw head/spring washer

combination, an optional flat washer, with an outer diameter no greater than 0.28 in(7.1

mm), may be inserted between the spring washer and the package bolting surfaces. Many

types of spring washer are available, such as split, conical, Belleville, and wave. The choice

of spring washer is left to the amplifier designer and choices may vary depending on the

application.

Finally, alternately tighten both screws in steps up to the recommended torque value using a

torque driver or equivalent. Depending on the choice of TIM, the final required screw torque

should be adjusted within the range listed in Table 4.

When the above procedure is properly applied, uniform pressure with tolerance for thermal

expansion is provided. The mechanical features designed in the STAC boltdown package

translate the force towards the center of the package at the prescribed screw torque. Along

with the material set featuring low creep and fatigue resistance, the STAC package and the

complete hardware system insure that pressure is maintained uniformly over time.

Table 4.

Recommended screw torque

Minimum

Typical

Maximum

3.5 in-lb

5.0 in-lb

6.5 in-lb

0.4 N-m

0.6 N-m

0.75 N-m

4 kg-cm

5.8 kg-cm

7.5 kg-cm