Drive para soldadores

The drive for Pb-free solders in the microelectronics industry presents several new reliability challenges. Examples include package compatibility with higher process temperatures, new solder compound failure mechanisms, and the selection of the proper Pb-free alloy to maximize product lifetime. In addition to the challenges posed by the Pb-free material conversion, the migration of market focus from desktop computing to portable applications is changing the critical system failure mode of interest from conventional temperature cycling (T/C) induced solder fatigue opens to drop impact induced solder joint fracture. In this paper a study was conducted to investigate the influence of intermetallic compound (IMC) growth on the solder joint reliability of Pb-free ball grid array (BGA) packages under drop loading conditions. Thermal aging at homologous temperatures between 0.76 and 0.91 with microstructural analysis was conducted to analyze the solid phase IMC growth at the solder to BGA pad interface. Component level,ball shear and pull tests were also conducted to investigate the aging effect on solder joint strength. A key finding from this work is that Kirkendall voids formed at the bulk solder to package bare Cu pad interface under relative low 100°C aging. Void formation and coalesce is shown to be the dominant mechanism for solder joint strength and board level drop reliability degradation.

The electronic packaging industry has been using electroless Ni(P)/immersion Au as bonding pads for solder joints. Because of the persistence of the black pad defect, which is due to cracks in the pad surface, the industry is looking for a replacement of the Ni(P) plating. Several Cu-based candidates have been suggested, but most of them will lead to the direct contact of solder with Cu in soldering. The fast reaction of solder with Cu, especially during solid state aging, may be a concern for the solder joint reliability if the package will be used in a high temperature environment and is highly stressed. In this work, the reaction of eutectic SnPb solder with electrodeposited laminate Cu is studied. Emphasis is given to the evolution of the microstructure in the interfacial region during solid state aging and its effect on solder joint reliability. A large number of Kirkendall voids were observed at the interface between Cu3Sn and Cu. The void formation resulted in weak bonding between solder and Cu and led to brittlefracture at the interface in the ball shear and pull tests. The experimental results indicate that a barrier for Cudiffusion may be needed between the solder and the type of Cu used in the test vehicle for the packages that will experience high temperature (>100°C) and high stress.

© 2005 American Institute of Physics

Received 10 Agosto 2004 Accepted 02 Novembro 2004 Published online 23 Dezembro 2004

Acknowledgments:

The authors would like to acknowledge B. Holdford and J. Saekhow for their assistance in experimental analysis. Valuable discussion with Masood Murtuza is greatly appreciated.

Article outline:

I. INTRODUCTION

II. EXPERIMENT

III. RESULTS

A. Interfacial microstructure

B.

...