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Big Spy Glass Moves Into Assembly To Catch Small Defects

Component packaging and the PCBs, themselves, are getting increasingly smaller. Many OEMs continue to use traditional size boards, but today, there are growing numbers of smaller and portable products being introduced.

Traditional board inspection involving x-ray and automatic optical inspection or AOI has played a vital role in assuring product reliability. However, now with shrinking PCBs and smaller packaging, and considerably less board area for laying out a design, a relatively new form of close up inspection is being used. This relatively new inspection is called forensics and is tailored to significantly improve reliability and in many cases, save a PCB design that otherwise is discarded because elusive defects cannot be found.

Fig. 1

Most often a design is ìthrown over the wallî with the hope AOI and x-ray will find problems unexpected problems. But it usually doesnít occur to designers that conventional inspection may not be able to catch the small defects. At this point, forensics steps in to take over from conventional inspection to uncover elusive defects. For example, Fig. 1 shows a micro hairline fracture on a BGA ball that was not caught by conventional inspection.

Check out our recently published tech articles (below) to find out more about both conventional inspection and forensics analysis:

For the time being, here are some examples of what forensics can uncover in a faulty design:

  • In the case of buried vias, air bubbles created by plated contamination and trapped between via walls can be uncovered. These air bubbles can create intermittent connections.
  • A cross-section of a package-on-package or PoP is forensically analyzed to show BGA balls with head-on-pillow defect.

  • Thickness of copper (Cu) plating on through holes and vias is investigated.
  • On a gold immersion surface board, gold plating thickness is checked out to determine if the right amount of gold has been deposited per fabrication spec.
  • On an ENIG surface board, assurances are made that the base nickel plating — before gold is deposited ñ is performing according to the spec sheet.
  • Checks and uncovers potential solder thermal fatigue and current leakage failures, especially prevalent in PoP-populated PCBs.

Without the tools and techniques of forensic analysis, the OEM can be at a loss of thousands of dollars and in some cases tens of thousands of dollars, on top of spending countless hours of rework, debugging time, not to mention delays in product launches and lost revenues and so on.

Now, conventional inspection is partnering with forensics analysis to do detective work and sleuth around the insides of a package on package (PoP), for example. This newest of inspection techniques ñ using scanning electron microscopy (SEM) and time domain reflectometry (TDR) — is increasingly making its way into the PCB assembly floor with its bag of tools to investigate and detect the smallest of culprits causing board defects.