Automating the Rework Process

Bert Kelley, Technical Specialist
Orbotech, Inc., Billerica, MA USA

Automated Optical Rework (AOR) is a new method of reworking shorts by using a fully automated fine laser beam to ablate any excess copper in fine-line PCB patterns. This includes shorts, protrusions, copper splashes, minimum space violations, under etched conductors, excess features and more, without damaging the panel's substrate.

In the traditional PCB production process, following automated optical inspection of a panel, the operator of the verification system manually reworks any excess copper using a knife. Manual rework can damage the adjacent conductor, penetrate the laminate, create cosmetic defects in outer layers and more. In fine-line production (sub 60micron), quality manual rework is not possible, even by highly skilled operators.

This includes, for example, the most advanced smart phone designs with line and space of sub 50micron and prepreg lamination thickness of 40micron and below. In addition, many PCB shops' customers prohibit manual rework of PCBs.

The technological solution for automated rework that has been developed offers:

• Support for fine-line products (down to L/S resolution of 30).
• Fast rework - typically 60 reworks per hour (including handling) for typical high-end HDI production
• High quality - minimum damage to laminate; typical penetration of 15 or less
• Accuracy - deviation from reference of less than 10%
• Repeatability - all reworks are of the same high quality
• An automated process - no human intervention

AOR introduces a closed-loop technology of iterative processes that consist of three parts:

• Image acquisition - captures white-light and UV images.
• Image processing - analyzes and compares the images with the CAM reference data and defines the accurate ablation
contour and parameters.
• Laser ablation - based on the processed data, shorts are reworked using laser ablation

The quality results of AOR are now well-proven for even the most complex PCB designs. The latest technology breakthrough in higher speed with no compromise on rework integrity has cleared the way for more widespread and mainstream use of this technology in the manufacture of today's demanding PCB applications.

This technical paper will describe Automated Optical Rework technology and its advantages for advanced printed circuit board production including examples of actual before and after results.

Based on years of extensive research and development as well as rigorous testing in production, the quality results of AOR are now well-proven for even the most complex PCB designs. The latest breakthrough in higher speed with no compromise on rework integrity has cleared the way for more widespread and mainstream use of this technology in the production of today's demanding PCB applications.

The advantages of AOR provide new opportunities for fabricators to move much closer to achieving zero scrap production, while continuing to push the boundaries of electronics innovation.