This document summarizes an X-ray inspection workshop that covered common defects seen in electronics manufacturing and how to identify them using X-ray imaging. The workshop discussed why X-ray inspection is used, suggested requirements for X-ray systems, and provided examples of defects like BGA opens, voids, cracks, and dendrites. Attendees were taught inspection procedures and criteria to evaluate components like BGAs, QFNs, and through-hole joints using X-ray imaging.
5. Why X-ray Inspect?
Non-destructive test for optically hidden joints
(e.g. BGA’s, QFN’s, Connectors) & internal
package details (Ball Bonds, Wedge Bonds)
Field failure analysis
Process development
Production quality control
Set-up changes
New Product Introduction (NPI)
Verification for Rework
6. High magnification at Oblique Views
Application Support
Digital Processing
Sub Micron/High Power
High resolution (1.3 MP or more)
Good separation of similar grey levels within the
x-ray image (65,000 Levels)
Oblique views around point of analysis (Rotation)
Ease of use
Suggested Requirements for X-ray Inspection
9. 9
PCB Pad
BGA
Ball
Solder Paste
Pad
PCB
2 x circles on the x-ray
image show BGA
connection are OK
PCB
Solder Paste
BGA
Ball
If open connection, the
circle on X-ray image
will not be seen
X-Ray
“OPEN Connection”
Inspection Logic
10. Proper BGA Wetting Principles
1. Solder ball is more dense than PCB
pad
2. If proper wetting occurs the lighter
density PCB pad shares its density
with the ball.
3. That being the case, the pad will
show up as a lighter color than the
ball if a homogenous bond is created.
4. If proper wetting does not occur then
the pad will carry it’s own density
properties and will show up as a dark
mass outside the perimeter of the
BGA.
11. When the two masses do
not share a common
density, the PCB pad is
exposed and an open
solder joint is detected as
indicated in the image on
the left.
BGA Open
12. Strength of x-ray inspection is being able to look
for opens, voiding, fractures and generally monitor
production quality.
Also - able to prove to your customer that the
reflow quality is good - BGAs are often forgiving of
process variations - incl. Pb-free
Combat the frequently heard phrase from your
customer - “The boards you sent me do not work! It
must be how you soldered the BGA!”
Using XRAY for BGA Inspection
13. Common BGA Opens
Cold Profile or Cold spots (visible solder-paste spheres)
Hot Tears; caused by rapid cool down using lead free
paste
Head in Pillow
Exposed Pad on PCB……..Indicative of Profile not quite
hot enough to create an inter-metallic bond. Could also
point to contaminated components.
Excessive Voiding Cracks or Fractures due to stress.
Clogged Aperture on stencil
Bridging
30. Recommended BGA Inspection Procedure
Always inspect at an Oblique Angle for Opens
Check corners – shows lifting or Potato Chipping
Work your way into the centre.
This will Most likely to be the last point to reflow if any
substantial ∆T is present
All terminations should be reasonably circular and
consistent in size
Voiding, opens (non-reflow), HIP, Partial Wetting
Inspect whole of BGA after rework – gives confidence in
the process
40. Cracks & Breaks
Copper tracks or in Solder Joints
Die cracks:
Fatigue from thermal cycling
External stress (dropping)
See an absence of material in x-ray image (from lower density)
May need oblique view to see