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The View Inside
Why to inspect solder joints with X-ray?
The reliability of electronic assemblies strongly depends on solder joint quality. Acceptability criteria are mainly based on shape
and dimension of the solder joints. As quality demands and technology for assembly process for new package types increase,
many solder joints are no longer directly visible. Fortunately, they can easily be inspected by advanced microfocus and nanofo-
cusX-raysystems.phoenix|x-rayoersdedicatedanalysisandautomaticinspectionsolutionsforanytypeofsolderjoint:
BGA: voiding
BGA: solder bridge
BGA: insufficient reflow
BGA
PCB
Scheme of a BGA solder joint , X‑ray image of a BGA solder joint
(top‑down view)
BGA: warpage
All dimensions and features of the solder joint are imaged: diameter,
thickness (grey value), lands and contact areas (darker and brighter
circles), voids (bright spots). All defects that have any influence on the
solder joint's shape are detectable:
Bridges, opens, missing joints, warpage, popcorning, component tilt,
voids, diameter deviations, roundness, shape deviations (roundness),
fuzzy edges (insufficient reflow), misregistration.
BGA type solder joints such as PBGA, CBGA, CGA, etc.
SMD: crack
SOT: defective paste print
MLF: two open joints
Lead
PCB
Scheme of a Gull Wing (QFP) solder joint, X‑ray image of a QFP
solder joint (top‑down view)
QFP: weak heel fillet
In addition to toe and side fillets the X-ray image reveals hidden fea-
tures of the interconnection: the heel fillet which is most important for
the reliability of the solder joint and voids.
Detectable defects: Bridges (in particular under the component),
opens, defective paste print, insufficient co-planarity, incomplete fil-
lets, de-wetting, insufficient reflow, mis-registration, cracks.
Gull Wing and flat ribbon solder joints such as
QFP, SOT, PLCC, Chip devices etc.
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