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Inspection Guide Illustrates Defects
March 19, 2007 |Estimated reading time: 1 minute
FREMONT, Calif. David Bernard, Ph.D., introduced A Practical Guide to X-ray Inspection Criteria and Common Defect Analysis as a teaching aid and reference guide. Information in the book, published by Dage Precision Industries, covers an introduction to X-ray equipment, including several definitions; theories for effective use of automated X-ray inspection (AXI); and methods for detecting faults in PCB assemblies (PCBAs). Appendices give readers a guide to purchasing X-ray equipment, frequently asked questions (FAQs), and several references for further study.
While Bernard acknowledges different types of X-ray systems, such as laminography and computerized tomography (CT), he focuses on implementation and capabilities of 2-D systems, as these are the most common in the industry. A majority of information revolves around BGA, flip chip, and other array devices that prove difficult to inspect with automated optical inspection (AOI) techniques. While thru-hole soldering is referenced, the guide deals primarily with the defects and inspection techniques relevant to surface mount components. Special attention is paid to reworked boards and the circumstances surrounding lead-free and mixed-assembly defects. Voiding, particularly with BGA devices, is the "most common fault detected," and therefore Bernard invests most attention in directions and information in void detection.
The guide offers X-ray images alongside definitions of defects and components, "to show recommended inspection criteria and typical defects" in a visual manner. While some images depict the benefits of color-filtering which can expose voids within a BGA better than straightforward grayscale imaging most are high-magnification, top-down and oblique, grayscale views of a particular lead, component, or trace. Some illustrate inspection criteria, others expose a particular defect, and more are used to show target, acceptable, and defective conditions for a given chip component, LGA, flip chip, etc.
The guide attempts to leave X-ray users, students, and those managing an assembly line or purchasing equipment with a sense of the what, why, and where related to defects and X-ray systems. Simplified equations explain the principles behind X-ray inspection, and suggested inspection regimes are designed to benefit board assemblers. In the "X-ray Checklist," Bernard lists important questions to ask of equipment manufacturers, such as "What is the system configuration? Is the X-ray tube above the sample or is the detector?," and oft-overlooked information such as maximum board size and maximum inspection area. Manufacturers may not always explain that these two are not always equal. For more information on the guidebook, visit the Dage Website.