Effect of sampling rate on the accuracy of strain gage measurement during printed circuit board functional test

Strain gage measurement is widely used in electronic industry as an effective tool for assessing and controlling risk levels. However, the accuracy of strain gage measurement is easily influenced by many factors, among which sampling rate/scan frequency setting of a measure equipment remains an important one. Some critical strain values may be missed if the sampling rate is too low, on the contrary, if the sampling rate is too high, unnecessary time and cost will be wasted on data analysis. In this paper, the effects of sampling rate on the accuracy of strain gage measurements during printed circuit board (PCB) functional tests (FCT) were investigated by comparing the diagonal strain (εd), principle strain (εp), and strain rate of a laptop PCB ranged from 1 to 1k Hz. The test results showed that all the above indicators reduced with decreasing sampling rate, especially for the sampling rate less than 250 Hz. The acceptable sampling rate for accurate strain measurement was defined as the sampling rate at which less than 1% decrease in the indicators compared to those at a sampling rate of 1k Hz. The minimum acceptable sampling rate for the laptop PCB during FCT were 333, 333, and 500 Hz based on εd, εp, or strain rate, respectively. Although the difference between minimum acceptable sampling rates based on two different strain metrics was not significant, the values of principle strain were always higher than the that of diagonal strain around four corners of a array-based package soldered onto the PCB. The minimum acceptable sampling rate based on strain rate was most conservative, followed by based on εp, and εd. The higher strain rate at a sampling rate of 1k Hz, the higher minimum acceptable sampling rate was required. However, the dependence of minimum acceptable sampling rate on ep and εd is not significant.