AOI First Article Inspection
Process Overview and ROI

High-Mix / Low-Volume (HMLV) manufacturing environments (typically CMs) can save big by improving efficiency through AOI First Article Inspection.

• Know the first board is assembled in accordance with the BOM
• Know the pick-and-place machine is correctly configured
• Know that parts have been placed into the feeders in the correctly
• Know that the reflow oven settings are correct
• Eliminate 99.9% of human error related faults

AOI, First Article Inspection Process Overview

A populated reflowed PCB is scanned into the system. The CAD data is then imported, directly from the pick-and-place or line-control software. The operator has all relevant data required to perform the inspection. Because the X and Y coordinates are associated with the pick-and-place data, the AOI system displays an exploded view of the part with its associated data on the screen. There is no requirement to locate parts manually.

The BOM data (reference designator and part-numbers) are imported along with the CAD for cross-checking relationships the pick-and-place data (see image). The operator establishes the fiducials on the PCB, and then inspects the PCB as each part is displayed on the screen with its associated data (part numbers, reference designators, etc.). Any differences are brought to the operator’s attention automatically in AOI mode or by observation using Comparator mode.

For the first PCB of any type ever inspected, all of the data on the BOM is stepped through with the image on the screen, showing a greatly expanded view of the part being inspected. The operator does not need to worry about checking off parts in the system, as the data contained in the BOM came from the SMT loader - making it 100% accurate. The location on the PCB is displayed automatically, enabling the operator to concentrate on the visual inspection of parts loaded on the PCB.

The system will track all parts inspected to ensure that the inspection is complete. Once the inspection is complete, the operator saves this known-good sample and data for subsequent runs. On these runs, the operator loads the sample, while the system compares the PCB being inspected against a known-good sample with respect to the BOM and CAD data. This would virtually guarantee that the setup of the pick-and-place machine is the same.

Risk Analysis

If a company produces 10 million parts a month on PCBs, the first article inspection process would check about 20,000 of them. If human error leads to one problem in 1,000 (considered very good), there would be a potential of 20 problems each month. If each of those 20 problems were associated with reels of 5,000 parts, then 30,000 parts are placed incorrectly every month. Even if only 10% of reels were used each time on average, there would be 3,000 parts incorrectly placed each month. Using an automated first article inspection system ensures 100% of the parts are inspected, and could eliminate 99.9% of these problem types.

In a recent return-on-investment (ROI) study at a medium-size CM was shown that cost savings could be achieved by automating the first article inspection process. Because their customers are in the medical and military markets, it was required that their first article be completed before manufacture. For an average-size PCB with 400 surface mount components, it was taking 15 seconds to locate and check off each part. This equals 1 hour, 40 minutes during which the line is not producing - with a lost opportunity cost of $1,650. Considering that they have five SMT lines with changeovers two times a week, the total lost-opportunity cost was calculated at $16,500/week. Once automated inspection was implemented, the average time to perform the same task was reduced to 15 minutes, a 65-minute savings per inspection (See Chart). This calculated to $10,830/week in savings, or 10.83 hours of lost opportunity on SMT loaders.

Conclusion

An automated first article inspection system aids in the accurate setup of a pick-and-place system. It can reduce the time spent performing this process - speeding production and eliminating errors in manufacturing. Cost savings also are difficult to ignore. Using an automated first article inspection system allows the SMT work cell to become an integrated department that verifies its output according to customer requirements for overall process control.

Call (858) 536-5050, for more information

Credits: Risk and ROI Analysis w/ Chart,
SMT Article, Feb. 2007 - Greg Ross(CEO), Cluso Vision Systems