PSI - Issue 18

Alexandru Falk et al. / Procedia Structural Integrity 18 (2019) 214–222 Falk A./ Structural Integrity Procedia 00 (2019) 000–000

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In Fig.5 is shown the way in that PCB is bended due to difference in height of bumps which are 0.2 mm above the PCB seating surface. Screwing sequence for every of the 4 screws is: 0.25 Nm, 0.4 Nm, 0.55 Nm, 0.7 Nm. The screwing positions (Screw 1 to Screw 4) which were done by screwdriver Holex in sequence are shown in the figures below.

Fig. 5 PCB bending.

2.2. Strain gauge measurements Three areas at microprocessor corners were considered on PCB where strain gauges rosettes were placed, and strain measured, Fig. 6. Strain gauges used are HBM RF91 (right angled gauge rosette) with the following characteristics: 120 Ω resistance, three gauge placed at (0°, 45°, 90°).

Fig. 6 Strain gauge rosette placement on PCB.

Data acquisition was carried on with QuantumX MX1615B and analyzed with Catman Easy V5.3.1 software. For each grid, one quarter bridge channel is required. In total, three channels are required to perform the measurement calculations with RF91, Fig.7.

Fig. 7 QuantumX MX1615B.