Current processes and procedures to clean electronic assemblies manufactured with tin-lead materials must be reviewed and updated when changing over to lead-free materials.  Inspection procedures and processes, applicable to products built with tin-lead materials are now considered inadequate when using lead-free materials. 

Electronic manufacturers converting to lead-free solder materials, are investigating x-ray inspection systems to enhance or re-build their acceptability/quality standards.  X-ray equipment featuring a two-dimension x-ray process, provides basic x-ray shadow micrographs as the x-ray light source bombards the sample with x-rays.  As different materials within the sample absorb the radiation, multiple shadows are captured by the detector.  When subjected to an x-ray light source, solder and copper traces appear darker than the laminated circuit board substrate; the denser the material, the darker the shadow.  The detector converts the resulting x-rays into an optical image for the operator to view and evaluate.  Magnification of the sample is achieved by moving the x-ray light source closer to the sample.

X-ray settings, consisting of tube power and accelerating voltage, have a direct bearing on the quality of the resultant image.  Although more power will produce a brighter image, there are technical limitations on the maximum power x-ray tubes can accept.

The image obtained from an x-ray light source passing through a sample is based on multiple factors including the density and atomic number of the sample materials. Solder materials containing lead are denser and have a high Z atomic value; solder materials without lead are less dense and have a lower Z atomic value. Usage of the same power tube setting to inspect lead-free solder material and solder material with lead will result in the lead-free solder material image being over exposed.  X-ray settings must be appropriate for the types of material being inspected.

Leading manufacturers of x-ray equipment have developed and implemented advancements in technology for lead-free solder materials including comprehensive contrast and power adjustments, providing for more accurate and repeatable results. In the past many x-ray systems employed a closed x-ray tube which was sealed, preventing access to the tube components. Technology driven, x-ray equipment suppliers now offer open and/or changeable power tubes as these tubes provide higher magnification and resolution.  Cost reductions pertaining to maintenance and serviceability are achieved by permitting access to key components within the power tube.

The selection of x-ray equipment should be based on the product and production requirements, power tube configuration, operating system, reliability and physical location in the factory.  One aspect of the equipment location that is often over looked is vibration.  Image resolution can be significantly degraded by the ambient factory vibrations.  The solution can be as simple as shock pads under the legs or as complex as constructing an isolation mounting pad to eliminate the problem.  Most x-ray suppliers can conduct a site survey to determine the best location and vibration mitigation strategy. 

Two terms that are commonly used when defining x-ray capabilities are ‘focal spot size’ and “minimum feature size”.  Focal spot size has a direct relationship to achieving high image resolution;  “minimum feature size” relates to a combination of object recognition processes. Focal spot size and image resolution are significantly influenced by the image- capture device, and the image processing system.  When the focal spot size is reduced to meet the requirements of smaller component package types, exposure time must be increased to generate sufficient image quality. However, when the expose time is increased, thru-put is significantly reduced.

The x-ray selection process should recognize and consider for value the many different features available on today’s systems.  Purchasing a high resolution x-ray system is not only a significant investment of capital but also represents a significant investment in analytical capability and is an invaluable process control tool for the factory. 

For additional information on Dage X-Ray equipment or to schedule a demonstration of the Dage X-RAY equipment located at the EMPF, please contact Robert N. Berta by telephone at
610-362-1200 ext 253 or via e-mail at rberta@aciusa.org.