| Basic Knowledge |
How to select strain test system?
The key to choose a strain test system is select the right strain gage, data acquisition instrument, and strain test software.
Select strain gage:
The IPC/JEDEC-9704 guideline document recommends using three-element stacked rosette strain gages for PCB strain gage tests, details of the recommended strain gage are as follows:
 Three-element stacked rectangular (0/45/90) rosette strain gage
1.0 to 2.0 mm, 2 nominal, gage sensor size
120 or 350 W strain gages
Lead wire attach pads located at or lead wires attached on one side of strain gage
Select data acquisition instrument:
We recommend paying attention to the following parameters while running the test:
Scan frequency (sampling rate)
Sampling resolution and gain setting
Number of channels
Scan frequency: We often call it sampling rate, is the rate at which data is sampled in the units of number of samples per second (Hz). For PCB strain gage tests, a minimum scan frequency of 500 Hz is recommended, although typical scan frequencies range from 500 Hz to 2 kHz. This sampling rate ensures the capture of any high-frequency dynamic events that may occur.
Sampling resolution: It refers to the number of bits of the analog-to-digital converter (ADC) in the data acquisition hardware. The higher the resolution, the smaller the input signal changes which can be detected and the more accurate the measurement. For PCB strain gage tests, a minimum sampling resolution of 12 to 16 bits is recommended.
Number of channels: The number of available monitoring channels limits the number of measurements in one pass. At least 12 measurement channels are required to monitor four stacked rosettes mounted at all corners of a BGA chip.
Select strain test software:
The most basic function of strain test software is to read and record the strain values when assembly and test processing. But for the user, just record the data is not enough, it should contain configuration of hardware, data analysis, report generation and friendly HMI.
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