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SMART Group launches “Lead-Free Process Defect Guide 2”
Real-Time X-ray Inspection
would result in bent leads. Although the than removing the component. It’s worth a
for Quality Control and
package when opened did have a desiccant try, but inspect the component location after
Process Development ...
bag, there was no evidence of a relative with optical or x-ray equipment.
humidity indicator strip, which should also
Glenbrook’s
be present to show. High levels of humidity
can lead to popcorning/cracking of the
component body during reflow. Examples
of cracking are also provided in the defect
section of this guide.
Lead-free wave solder skip
Figure 8 is a solder skip mainly due JewelBox 70-T
™
to incorrect wave height as there is
�
80 kV
�
no evidence of solder on the pad or
10 micron focal spot
�
Up to 2000x
termination. This may be a lead-free joint, magnification
but the principle behind the defect is the
�
5-axis minipulator
same on tin/lead processes. If there had
allows tilt & 360º
rotation
been solder on the termination, the process
Figure 9. Soldering balling under a BGA.
parameters may have been correct; problems
JewelBox 90-T
™
with the pad solderability may have existed.
�
90 kV
In the past, skips have also been BGA ball damage
�
5 micron focal spot
�
Up to 2000x
seen with different component suppliers It is unfortunate, but mechanical testing of
magnification
and different lead forms on this type of joints can happen on production boards, � 5-axis minipulator
capacitor. This type of component has and the result is shown in Figure 10, where
allows tilt & 360º
the highest stand-off for parts used on the ball has been broken off the BGA
rotation
wave solder designs. When investigating and the pad. Probing BGA joints is poor
skips, look at the design, differences in practice when inspection techniques like
component lead form, and process issues x-ray and endoscopes are readily available
like flux gassing and wave height variation. in manufacture.
Great care needs to be taken by skilled
staff if testing of suspect joints is to be
considered. It is clear from the damage to
The GTI-5000
™
the ball surface that the joint surface has
Image Processing
Software
been subjected to a high force. It is very
�
Standard with
easy to apply well over 1 kg of force with any JewelBox
a toothpick, and this type of action should
�
Easy to use
�
be avoided or very well documented.
Fast and accurate
testing routines
�
Fully networkable
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Figure 8. A solder skip most likely caused by
incorrect wave height.
Solder balls on BGA
Figure 9 shows a good example of solder
balling under a BGA that is certainly
outside of the IPC criteria. The ball will
Figure 10. The ball here has broken off the
have undoubtedly reduced the insulation
BGA and the pad.
separation distance below the minimum
for the product design; however, reworking
the component to remove it may be Bob Willis is a process engineer providing
extreme. The solder ball is most likely engineering support in conventional and surface
a result of using paste to rework the part; mount assembly processes. He runs special
JewelBox 70-T
™
excessive paste resulted in a solder ball. production features at exhibitions and also
In the case of rework, it’s worth looking offers his seminars and workshops worldwide.
at the new dip paste, as it can eliminate These complement his own practical hands on
rework stencils. workshops. For further information on how Bob
With care and a height pressure air line, may be able to support your staff with on line
the ball could probably be removed rather consultancy go to www.ASKbobwillis.com
11Emery Ave., Randolph, NJ 07869 USA
Tel:973-361-8866 • Fax:973-361-9286
Toll Free: 800-600-8866
www.globalsmt.net Global SMT & Packaging - August 2008 – 7
www.GlenbrookTech.com
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