M.S. Thesis Presentation by Hernán Mercado-Corujo
Monday, March 5, 2001

(Dr. Suresh Sitaraman, advisor)

"A Study of the Thermo-Mechanical Reliability of Plated-Through-Hole / Press-Pin Assemblies"

Abstract

Plated-Through-Hole/Press-Pin (PTH/PP) reliability continues to be an important concern in the electronic packaging industry. At the 2nd level of packaging, through-hole components (such as DIP and PGA, among others) account for more than 50% of the IC packaging on a typical PWB. Others, such as discrete and optical and RF components, remain through-hole. In addition, connectors, used at the 2nd and 3rd level, constitute 21% of the microelectronics market. Continued introduction of new materials, geometries, and processes result in new design challenges. The connection attained by compliant press-fit pins is a determinant factor in the integrity and continuity of electrical signals. PTH/Press-Pin assembly studies are limited and simplified, not fully modeling the interaction between both. Design challenges involve many details, from geometry to stiffness and degree of interference. A small PTH will lead to the damage of its wall by a Press-Pin and could induce Press-Pin buckling during insertion. A big PTH could lead to loss of contact at temperature extremes during thermal excursions. In addition, the plastic deformation on both the pin and the PTH could affect the fatigue life of the assembly, since the Press-Pin insertion could induce cracks on the PTH at the moment of insertion.

In this work, a combined numerical and experimental program has been developed to address the challenges mentioned above. The press-fit pin connection in a PTH is modeled in 3D for reliability studies, taking into consideration material non-linearities and contact behavior. The study intends to determine the stresses induced in the PTH under mechanical (including PP insertion) and thermal loading. In addition, mechanical reliability will be studied due to the possible development of fatigue cracks. This work intends to understand the different mechanisms affecting the reliability of this type of assembly in order to recommend optimum design parameters, such as hole and plating diameter and pin insertion force. Numerical 3D models have been developed and validated through known approximate analytical solutions. Experimental data, both mechanical and electrical, has been gathered to validate the numerical models used in the study. Two different types of pins have been assessed for reliability under three different metallurgies and three different hole sizes.