Strain gauge measurements are recommended to be done at each process step that has the potential to cause excessive board flexing leading to solder joint cracking. Assembly processes where strain gauge measurements are recommended include:
- 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 should be in the range of ±500 μstrain. Dye and pry analysis is required to confirm if the measured strain causes solder joint cracking. It is recommended to conduct dye and pry analysis for any strain reading greater than 500 μstrain. To reduce the affects of strain on a device, edge bonding can be used and is recommended for larger packages. See Edge Bonding Guidelines for implementation details.