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www.us-tech.com 3D X-Ray Inspection Provides Quality Check of Double-sided PCBs By Andreas Tuerk, Team Manager AXI Division, Goepel electronic GmbH T
oday’s electronics are more compact, complex and faster than earlier versions of the
same products. Smaller products demand reduced power usage along with lower costs. Space saving tech- niques used to accomplish these goals includes newer component packages with hidden leads under the body. Combining these packages with double-sided PCBs allows for high performance assemblies with a smaller footprint. This trend pres- ents new challenges for test and inspection technologies. Solder joints hidden beneath
components such as BGAs, can only be evaluated by “looking through” a PCB. X-ray inspection technology takes over where conventional AOI systems reach their limits. 2D x-ray systems are limited when used to inspect double-sided PCBs, providing an image of one side superimposed on the other. This means that obtain- ing a detailed, process-reliable evalu- ation becomes impossible. 2.5D inspection provides a better fit yet does not yield an ideal view. An angled PCB X-ray depends on radia- tion angle and board thickness pro- viding a separation of the solder joints on the top and bottom side assemblies. Dense component lay- outs pose a challenge to a simple angle X-ray that produces insuffi- cient results. Similar to the 2D tech- nology, superimposition of the top and bottom sides prevents satisfacto-
2D x-ray: Superimposed solder joints on PCB top and bottom sides makes evaluation of a single side impossible.
ry evaluation of the solder joints. Digital Tomosynthesis A 3D X-ray inspection system
3D X-ray: Separated solder joints on PCB bottom side permits evaluation of solder joints.
using digital tomosynthesis captures slices of the top and bottom side of a PCB from different angles. Captured 2D images are translated into 3D data via algorithmic reconstruction. The result is an image that is free of superimpositions showing a distinct separation of top- and bottom-side solder joints regardless of component density. Superimposed and electri- cally connected assemblies such as package-on-package (POP) can now be successfully inspected. The 3D reconstruction layer-by-layer enables suitable visualization of top- and bot- tom-side components to provide a successful evaluation of solder joints. 3D X-ray is an imperative for dou- ble-sided production lines.
Component Library Using a true geometric recon-
struction of the PCB from the CAD program allows for the use of a stan- dard component library. Users are able to generate a test program with the CAD data and component entries in the library quickly.
Compensating for PCB Warp A successful solder joint analy-
2D, 2.5D and 3D X-ray inspection use.
sis requires an understanding of the topology of a PCB. Board warp, sag, wavy surfaces or skewed components
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