Damage Due to Lead Insertion in Through-Hole Connectors

Project Number: C94-06
Point of Contact: dasgupta@calce.umd.edu

Objective

Develop mechanistic predictive models to predict the damage caused in plated-through holes (PTHs) and in the surrounding printed wiring board (PWB) by the forces generated by compliant pins in an insertion-mount connector.

Background

There is significant evidence that local forces generated by the compliant pins of insertion- mount connectors cause local damage and permanent deformation to the PTH hole-wall. This leads to concerns over the reliability of the PTH, as well as to the possibility of damaging neighboring traces in fine-pitch technology. Current acceptance methods involve cross-sectioning samples and visually quantifying damage for each new configuration. Unfortunately, the lack of existing quantitative models of this failure mode requires ad hoc empirical acceptance standards that are expensive to implement and questionable in value. Further, the design and manufacturing variabilities of the associated geometric and material variables necessitates a very large test matrix in any empirical methodology. The connector industry estimates that the associated hidden factory cost is on the order of hundreds of thousands of dollars per year, a cost that is ultimately passed on to customers.

 One possible cost-effective solution is to develop and validate quantitative mechanistic models that can predict the magnitude of damage and deformation based on physical parameters of the system, such as pin diameter, PTH diameter, pin material, PTH plating material, PWB material, and plating thickness. Such models would reduce the need for highly repetitive and costly failure analysis for damage evaluation, resulting in significant cost savings to the industry as a whole.

Work Accomplished

• Developed an analytical simulation model to address the problem as a thin-walled plated through hole (PTH) cylinder embedded in an infinitely large printed wiring board (PWB) substrate and loaded internally by distributed forces exerted by the compliant pins of the connector. The analytical model has been formulated for radial and tangential pin loads, using Fourier series techniques. The tangential forces are a result of frictional forces. The model addresses nonlinear deformations by incremental loading techniques.
• Calibrated the model to match the calculated deformation pattern with the actual observed deformation of plating. Samples were provided by Consortium Member.