Hybrid Probing Regimes to Unmask Hidden Ball Grid Array Defects
Combining IEEE 1149.6 boundary scan vectors with deflection-assisted flying Kelvin probes isolates unmasked BGA head-in-pillow defects down to 4.5 micro-ohms.
Micro-Strain Testing
Deformation Analysis
Mechanical stress evaluation involves measuring the minute physical changes in a circuit board during assembly or operation. Micro-strain testing utilizes specialized gauges bonded to the laminate surface to detect the stretching or compression of the epoxy glass matrix.
Process Validation
The placement of the gauges is critical to capturing the peak stress points near large ball grid array components. During a micro-strain testing cycle, the board is subjected to typical handling forces such as those found in a routing machine or a test fixture. If the recorded strain exceeds the thresholds defined in standards like IPC-9704, the assembly process must be modified to prevent pad cratering or trace cracking.
This proactive approach identifies risky manufacturing steps before the product reaches the field.
Dynamic Recording
High frequency events like drop impacts or shipping vibrations can also be monitored using this technique. Because the response time of the strain gauges is nearly instantaneous, micro-strain testing can record the transient bending modes of the board during a shock event. The boundary of the test is reached when the strain rate exceeds the sampling capability of the data logger or when the gauge itself delaminates from the surface.
Engineers use these results to design better mechanical supports and to select more resilient laminate materials.