Binghamton University

 

CHARACTERIZATION OF THERMO-MECHANICAL BEHAVIOUR OF Pb FREE CERAMIC COLUMN GRID ARRAY - CCGA PACKAGE USING MOIRE INTERFEROMETRY

Prof. S.B. Park & Rahul Joshi

The worldwide ban on lead containing products has made the microelectronics industry incorporate ‘Lead (Pb)-Free’ measures in its components, solders and processes. Little reliability data is available for new generation, Pb-free packages such as the Copper Column Grid Array (CuCGA) package. Moiré interferometry and numerical analysis are therefore being undertaken to understand the thermomechanical behavior of Pb-free packages compared to conventional tin-lead packages. Displacement, strain fields, deformation modes and failure mechanisms are being studied.

U-field moiré image of left-side of CuCGA

 

3D solid model of left-side of CuCGA (Quarter symmetry)

 

Description

The CuCGA package is a 42.5mm sq. ceramic module assembled with 1657 (41x41) copper column interconnections for high reliability, high performance applications. The experimental study uses a high sensitivity moiré interferometer to analyze the thermo mechanical behavior of the CuCGA package. In-situ thermal deformations of the highest DNP (distance to neutral point) column are measured for an initial isothermal loading of ΔT= -75°C and subsequent accelerated thermal cycling of (-40°C) ~ (125°C). The deformed shape of the column and the distribution of inelastic strains are extracted from the displacement fields.

 

Results and Comments

The dominant deformation mode is bending of the column due to thermal expansion mismatch between the module and the board. The results are compared with those of tin-lead CCGA tested under similar conditions. Unlike tin-lead columns, where the failure occurs at the column near the tapering ends of the solder fillet and through the thickness of the column, in the CuCGA, the failure is found to occur first in the solder fillet at the solder-copper column interface and the crack propagates along the periphery of the copper column. The accumulated plastic deformation per cycle is larger in tin-lead columns compared to the copper columns. A deformation mechanism is provided to explain the nature of this failure.

 

Research sponsors : IBM Inc.

Publications :

  • S. B. Park, Rahul Joshi and Lewis Goldmann, “Thermo-mechanical Behavior of Lead-Free Copper and Tin-Lead Column Grid Array Packages” Paper submitted to the IEEE Transactions on Components and Packaging Technologies, September 2004
  • S.. B. Park, Rahul Joshi and Izhar Ahmed, “ Impact of Power Cycling on Organic And Ceramic Ball Grid Array Packages ”, Proceedings of the 10th International Congress of the Society of Experimental Mechanics, Costa Mesa, California, USA, June 2004
  • . B. Park, Rahul Joshi and Lewis Goldmann, “Reliability of Lead-Free Copper Columns in Comparison with Tin-Lead Solder Column Interconnects” Proceedings of the 54th Electronic Components and Technology Conference, Las Vegas, Nevada, USA, June 2004