Journal of SMT Article

PROCESS OPTIMIZATION FOR 1.0 MM PITCH CBGA

Author: Marie Cole
Company: IBM Microelectronics
Date Published: 1/1/2000   Volume: 13-1

Abstract: The ceramic ball grid array (CBGA) package is used today in a wide range of applications, because of its many advantages: high interconnection density; compatibility with standard surface mount technology (SMT) assembly techniques; excellent thermal and electrical performance; and high interconnectivity. Today’s CBGA applications include memory, logic, and microprocessors and are found in computer systems ranging from desktop to mainframe, with highest usage in work station and server applications.

As these applications, particularly the high-end work stations and network servers, demand greater numbers of interconnections, increasing the interconnection density is one means of providing a solution. Decreasing the interconnection pitch on the CBGA package from the typical 1.27 mm to 1.0 mm gives a corresponding increase in interconnection density. This increased density reduces the package body size for the same number of interconnections. For instance, 937 I/O are available on a 32.5 mm package with 1.0 mm pitch, instead of a 42.5 mm package with 1.27 mm pitch (1088 I/0).

The smaller body size conserves area on the printed circuit board, but the tighter pitch requires more advanced printed circuit board (PCB) groundrules, The smaller body size, with its reduced distance to neutral point (DNP), should improve the reliability on a per interconnection basis, although the advantage is tempered by a reduction in solder joint height due to a smaller solder ball. The appropriate geometries and process parameters must be chosen, however, for optimum manufacturing yield and reliability.

This paper will discuss the process development activities and experiments to determine the optimum structure for the 1.0 mm pitch CBGA package. Elements included in the evaluation are: printed circuit board groundrules, ball diameter and attach processing, solder volumes and other card assembly parameters, and card assembly rework processing. Both yield and reliability are considered in choosing the optimum structure and processes.

Keywords - Ceramic Ball Grid Array, Fine Pitch Ball Grid Array, card assembly reliability.



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