Automation of Solder Joint Inspection Procedures Utilizing Laser Induced Infrared

In the rush to automate assembly flow in the fabrication and assembly of electronic equipment, great strides have been made in all areas with the exception of solder joint inspection and rework. This paper focuses on an attempt to automate, at least in part, the inspection of printed wiring assembly (PWA) solder joints. The use of laser and/or X-ray equipment is causing quite a stir in the industry due to the fact that there finally appears to be a technique that may allow for automation of one of the most labor intensive, inexact, and costly tasks in any PWA assembly operation--the visual inspection of solder joint quality. As the complexity of PWA's increase, the number and density of solder joints are increasing. This trend is resulting in decreased efficiency in the inspection process due to the shear number of joints to be inspected, operator fatigue, and the subjectivity of the entire inspection process. In areas where absolute quality is critical, such as military products, this declining inspection effectiveness is being compensated for by the incorporation of multiple inspection-rework loops. These techniques statistically should result in the identification of all defects on a given assembly. However, the impact of this multiple inspection process is one of total disruption to the assembly flow in an automated shop. Laser induced infrared (IR) inspection has been under investigation by Texas Instruments' Defense Systems and Electronics Group for the past several years. Our thrust has been aimed at the incorporation of this technique into the inspection of PWA's that are fabricated for military customers. Extensive efforts have been expended in the determination of the strengths and weaknesses of the technique in an attempt to augment the human element in the inspection process.