IPC Stress Relief Lands and terminals shall be located by design so that components can be mounted or provided with stress relief bends in such a manner that the leads cannot overstress the part lead interface when subjected to the anticipated environments of temperature, vibration, and shock. Where the lead bend radius cannot be in accordance with Figure 8-9 in order to achieve design goals, the bends shall be detailed on the assembly drawing.

IPC Stress Relief The leads of components mounted horizontally with their bodies in direct contact with the printed board shall be mounted with a method that ensures that stress relief is not reduced or negated by solder fill in the lead bends. Leads shall not be formed at the body of the component or between the body of a component and any lead weld. The lead shall extend straight from the body seal or lead weld before starting the bend radius as shown in Figure 8-9.

IPC Stress Relief The requirements shown in Figures 8-9 and 8-10 should be implemented to prevent possible component damage, particularly glass-bodied parts. Lead bending equipment capability should be considered when selecting a lead configuration. The use of spacers under components not mounted directly in contact with the board is recommended.

IPC Stress Relief DIPs mounted directly to heatsink frames, as described in section , may have special stress relief provisions included. The inclusion of a pliable spacer material between the heatsink frame and the printed wiring board is an acceptable method for ensuring stress relief provided the resilient added material is of sufficient thickness (0.2 mm typical) to compensate for forces imposed during temperature change. Many of the pliable spacer materials tend to have low T g and high CTE characteristics, imparting more stress than no spacer at all.

IPC Stress Relief Any heat dissipation technique or device shall permit appropriate cleaning to remove contaminants from the assembly. Conductive materials used to transfer heat between parts and heatsink shall be compatible with assembly and cleaning processes.

IPC Stress Relief Components on Class 3 assemblies which for thermal reasons require extensive surface contact with the board or with a heatsink mounted on the board, shall be protected from processing solutions at the conductive interface. To prevent risk of entrapment, compatible materials and methods shall be specified to seal the interface from entry of corrosive or conductive contaminants. Note: Even totally nonmetallic interfaces that are prone to entrap fluids can have adverse effects on the fabricator's ability to pass required cleanliness tests.