From Leaded to Lead Free Assembly and New Packaging Technology Challenges

The migration to lead free connections in the microelectronic industry has brought forth many technical challenges, especially in the packaging technology area with respect to materials and processes. The two major drivers to these challenges are the higher melting point and the thermo-mechanical behaviour (less creep than SnPb alloy) of the replacement alloy. The higher melting point drives higher reflow temperatures during the packaging assembly as well as the card assembly and this requires the use of new materials. Higher stresses in the package can result in a reliability impact for the product. The challenge of these lead free related changes is exacerbated by other trends in leading edge organic packaging such as chip low K dielectric materials, larger package and larger chip dimensions and, reduced chip bump pitch. This paper provides the reliability results obtained through various lead free organic package test matrices and qualifications. The principal failure mechanisms are presented and are explained through material properties and finite element modeling studies. Details of the package technology qualification process and results are presented.