Identify defective PCBs
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Tests were done at a manufacturing facility in Europe to determine if problems could be identified when comparing the very-near-field emissions of good boards and problem boards. There was an issue that had been eluding detection; it showed as a poor RSSI reading and had been isolated to the IF chain. An EMxpert spatial scan comparison of the IF currents between a good board and the problem board indicated an issue at a location different from where the manufacturer had assumed the problem was. Further investigation uncovered a soldering issue with a single component.
A scan of the entire board at the IF frequency clearly showed a difference in the spatial profile.
Once it was confirmed that there was a problem at the IF frequency a focused analysis on the IF chain was done. Zooming in on the area of the IF right as it exited the first mixer showed a very-near-field variation immediately after the SAW filters.
After viewing the large variation in the very-near-field emissions at this location, a visual inspection of the board revealed the SAW filter highlighted in the image above was populated with a 90° rotation meaning no signal would pass through.