Journal of SMT Article

LEAD-FREE CARD ASSEMBLY AND REWORK FOR COLUMN GRID ARRAYS

Author: Marie Cole et al.
Company: IBM Microelectronics Division
Date Published: 1/1/2004   Volume: 17-1

Abstract: IBM introduced copper column grid array (CuCGA) interconnect as the lead-free replacement for the lead-tin solder column on the ceramic column grid array (CCGA) (Figure 1). Like CCGA, CuCGA offers a high reliability packaging solution, enabling the use of ceramic chip carriers with excellent electrical and thermal performance.

The move to eliminate lead in microelectronic packaging increases the complexity of processing large body size, high I/O packages. The development of manufacturable card assembly and rework processes in concert with the development of a new package interconnect structure is key to technology acceptance.

Copper column interconnect (CuCGA) has been designed to meet the requirements of manufacturability, reliability, and electrical performance. Optimization of the structure for manufacturability focused on the robustness of the column during manufacturing handling and the ease of card assembly processing. The resulting card-side solder joint is key to the reliability of the interconnect. The interconnect geometry also influences electrical performance [1]. Evaluating these competing factors determined the final column design [2].

This paper focuses on the development and reliability evaluation of the CuCGA card assembly and rework processes. The goal of the process development was to adapt the successful SMT assembly process for CCGA to the developing standards for lead-free SMT processing. Successful integration of the assembly processing of the CuCGA into the developing tin-silver-copper (SnAgCu, or SAC) card assembly process posed challenges in the areas of placement, reflow, and rework. The optimization of these processes, and the proof of successful results demonstrated by reliability evaluations, will be discussed.

Key words: CCGA, CuCGA, ceramic column grid array, copper column grid array, lead-free card assembly.



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