SMTA International Conference Proceedings


Authors: Zhen (Jane) Feng, Jacob Djaja, and Ronald Rocha
Company: Flextronics International
Date Published: 9/22/2002   Conference: SMTA International

Abstract: The benefit of automated x-ray inspection (AXI) has proven to be not only a good defect detection tool, but also an efficient device for SMT process improvement. By understanding the AXI limitations with accuracy and consistency of results, the data can be used real time to adjust process parameters. In manufacturing, we all agree that - Prevention is better than Detection, 1 but it can only happen with good and timely data.

The AXI is an effective test tool for solder joint inspection, and it usually detects about 90% of the total defects on a circuit board assembly.2 Although AXI detection helped increase In Circuit Test (ICT) yields by means of paperless rework, very little was accomplished in the way of improvement in defects per million opportunities (DPMO).

In March 2000, the AXI Flextronics team developed and implemented a process improvement strategy that continues to provide positive results. The combination of gauge repeatability and reproducibility (Gauge R & R), test strategy and development of an attribute database allowed the team not only to understand reliable data, but also to efficiently look at our SMT process issues for each individual product everyday.

Example: A complex networking assembly was processed through AXI with 100% component coverage. The assembly has 29,000 solder joints with 48 Ball Grid Arrays (BGAs) and 93 Quad Flat Packs (QFPs) and gullwings. We tested 7,940 boards from April 2000 to March 2001, and 3,085 from August to November of the same year. The AXI yield increased to 42% from 29% and the DPMO average decreased to 124 from 380. The functional test yield increased from 91% to 95%.

Our data suggests that further process changes can be made to achieve significant improvement in AXI DPMO and Yield. This paper discusses the utilization of AXI attribute data for reactive process improvement and the work in process to convert the AXI output data into a more preventive application tool.

Key words: AXI, attribute, variable, yield, and DPMO.

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