The purpose of acoustic screening is to weed out components with internal structural defects such as delaminations and voids before surface mounting. Counterfeit plastic packaged ICs are typically discovered when a Sonoscan® C-SAM® acoustic microscope is scanning trays of supposedly new plastic IC packages.
The operator may notice that some of the plastic IC packages have defects. When he looks closely at the acoustic images, he notices something else – that the internal defects look a lot like those one usually sees in IC packages that have been heat damaged or even “popcorned” during a surface mount process. In addition the internal features may be inconsistent – die size or die orientation, lead frame geometry differences, etc. The components in the trays may just not look consistent or they may look more like improperly handled devices.
Are these counterfeit parts? To find out more, additional Sonoscan (www.sonoscan.com) C-SAM methods may be used to inspect the same components by looking for 28 characteristics associated with counterfeit parts, including the following:
• Evidence of sanding on the surface of the mold compound beneath a “blacktopped” surface.
• Remnants of an old ink printed label, not completely sanded off, beneath the ”blacktopped” surface.
• Remnants of an old laser marked label, not completely sanded off, beneath the ”blacktopped” surface.
• The acoustic impedance value of the mold compound. If the parts are authentic, they should all have the same mold compound and the same acoustic impedance. If some of the parts are counterfeit, they may have come together from many sources, therefore having varying acoustic impedance values.
Along with the original suspicious appearance of the defects, these methods help to identify the authenticity of parts. Unfortunately it is quite common for components such as plastic ICs packages and capacitors to be stripped from “junked” PC boards and cosmetically refurbished for resale as new components.
Although verification of counterfeit status may be aided by optical and x-ray methods, C-SAM acoustic microscopy is unique in that it alone is sensitive to delaminations.