Source Intel :
https://support.intel.com/support/p...1593-prd483.htm
Any additional board stiffening devices are not necessary and should not be used. These include stiffening plates that install or are pre-installed on the underside of some non-Intel motherboards. Using such devices increases the compressive load on the processor package and socket, likely beyond the maximum load that is specified for those components. In addition, the processor's fan heatsink clip may be difficult or impossible to install correctly, potentially causing fan failure and improper operation, which would void the processor warranty. If your motherboard comes with a stiffening plate installed, please remove it before installing the boxed Pentium 4 processor. Use only the clip and heatsink that came with the boxed processor, and the retention mechanism attached to the motherboard.

Integrators should take care to select chassis that have adequate clearance between the motherboard and chassis wall (minimum 0.250 inch) to ensure the board's underside bend does not contact the chassis.