Perform strain gauge measurements at every process step that can over-flex the board and crack solder joints. Recommended assembly steps for strain-gauge measurements include the following:
- PCB router (during PCB loading/unloading into fixture and during the routing process)
- PTH solder assembly during top-catch loading/unloading
- Press fit assembly during press base and tooling loading/unloading and during machine pressing process
- DIMM memory (during PCB loading/unloading and during insertion/removal of DIMM)
- Heat-sink assembly process (during PCB loading/unloading and during entire screw assembly process)
- X-ray fixture (during PCBA loading/unloading)
Strain gauge measurements must be in the range of ±500 μstrain. Use dye-and-pry analysis to confirm if the measured strain causes solder-joint cracking. It is recommended to conduct dye and pry analysis for any strain reading above 500 μstrain. To reduce strain effects on a device, use edge bonding, especially for larger packages. See Edge Bonding Guidelines for implementation details.