Key design parameters affecting the reliability of PCB board through-hole

Thermal cycle fatigue failure of vias (PTHs) is one of the main forms of interconnect failure in electronic products. The evaluation of through-hole reliability is mainly divided into two steps, i.e., stress-strain evaluation is performed first, followed by low-cycle fatigue life evaluation. The above two models, namely the stress-strain evaluation model and the fatigue life evaluation model, are given in the IPC research report, as well as the relevant parameter information required for through-hole reliability evaluation.

In engineering practice, these two models are still mainly used to evaluate the reliability of PTH. IPC's PTH fatigue life evaluation model is based on the results of a large number of experimental data on copper foils. Due to the assumptions of the IPC method, its stress-strain evaluation model does not satisfy the boundary free condition of the end face of the PTH coating, nor does it satisfy the displacement continuity condition at the bonding point between the coating and the substrate. The stress calculated by this model is uniformly distributed in the PTH coating, but in engineering practice, PTH failure usually occurs at the hole shoulder position in the center of the coating. The experimental results of 39 groups of samples recorded in the IPC research report also show that 9 groups of the experimental samples did not fail, 2 groups of failures occurred at the corners of the pads, and the remaining 28 groups of failures occurred in the axial direction of the coating near the center. Courseware, fracture failure at the axial center of the coating is the most important form of PTH failure, which is consistent with the location where failure often occurs in engineering practice.

References In view of the above problems, IPC's stress-strain model has been improved. In the study of the improved model, it was found that the ratio of the thickness of the PCB substrate to the aperture (that is, the ratio of thickness to diameter), the ratio of the thickness of the substrate to the thickness of the coating, and the ratio of the radius of the substrate to the radius of the hole are the main geometric design parameters that affect the fatigue life of PTH. Based on the improved analytical model, the sensitivity of PTH fatigue life to these three sets of geometric design parameters is given and analyzed. Select the PCB geometric design parameters within the engineering value range, and the calculated sensitivity can be used to guide the PCB design and improve the reliability of the PCB and PTH.