Journal of SMT Article


Author: Anthony A. Primavera et al.
Company: Universal Instruments Corporat
Date Published: 1/1/1999   Volume: 12-1

Abstract: Ball Grid Arrays (BGAS) have emerged as a relatively robust area array packaging alternative for applications requiring high input/output counts on limited printed circuit board (PCB) real estate. Due to their leadless configuration, larger ball pitch, and compatibility with existing standard surface mount PCB assembly equipment, BGAs avoid a significant segment of the assembly problems encountered in fine pitch PCB assembly. However, while the use of BGA has been steadily increasing, it is not considered significantly widespread. The explosive growth in BGA development in recent months has been fueled by the promise of exceptionally high assembly yields.

One significant issue concerning BGA process development has been in the area of joint quality and inspection. Often BGAs are suspect in the test and burn-in stage of production due to inability to visually inspect the joints. While transmission x-ray inspection can assist in inspection of joint-related parameters such as voids, the impact on joint integrity is difficult to assess.

This paper addresses some of the factors that influence the formation of voids in BGA assembly. In addition, effects of void size and frequency on joint reliability are addressed. Factors that affect the formation of voids in BGA assemblies can be classified into several categories, including process methods, solder and flux materials, component ball alloy, attachment metallurgy, reflow atmosphere, and oxidation levels on solderable surfaces. The influence of several factors in each category is discussed.

The "process methods" category can be further sub-divided into equipment-related parameters such as reflow parameters, fluxing and solder paste deposition methods, and handling and storage conditions. This paper also considers the impact of void size and frequency on long-term joint robustness.

Key words: printed circuit boards, area array components, ball gird arrays, void formation, and reliability.

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