I'm looking to make a thermocouple reader using the Analog Devices
LTC2986 measurement IC, which I would like to use because it does almost all of the hard parts in making the measurement.
While reading the LTC2986 datasheet, I noticed two statements indicating that mechanical stresses on the IC can introduce errors.
Long-term stability will also be affected by differential stresses between the IC and the board material created during board assembly.
The mechanical stress of soldering the LTC2986 to a PC board can cause the output voltage reference to shift and temperature coefficient to change. These two changes are not correlated. For example, the voltage may shift but the temperature coefficient may not. To reduce the effects of stress-related shifts, mount the reference near the short edge of the PC board or in a corner.
I've seen similar concepts mentioned in the datasheet for TI's
REF54.
The long-term stability value is tested in a typical setup that reflects standard PCB board manufacturing practices. The boards are made of standard FR4 material, the board does not have special cuts or grooves around the devices or go through burn-in process to relieve the mechanical stress of the PCB. These conditions reflect real world use case scenario and common manufacturing techniques.
Can someone point me to an article or app note that outlines best practices for preventing or relieving mechanical stresses on an IC package? I would like to do my best here, even if I can't quantify the magnitude of the effect.
For what it's worth, my normal practice is to use 4-layer FR-4 boards and to solder by hand with tin-bismuth solder. I use this because it behaves mostly like leaded solder while being lead free. The bonus is that it has a lower melting point than even eutectic tin-lead solder. Maybe this assembly method results in lower stresses compared to reflow with normal lead free solder?