AN-9046 데이터 시트보기 (PDF) - Fairchild Semiconductor
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AN-9046 Datasheet PDF : 10 Pages
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Figure 4: X-ray image showing voiding caused by
normal process variation during reflow.
There are also several forms of micro-voiding,
namely planar micro voids and Kirkendall voids.
The mechanism of void creation is different for
each; however both are practically undetectable by
x-ray inspection. Both types are also currently the
subject of several in-depth studies; however, none
have confirmed theories of creation.
Planar micro voids, or “champagne voids” occur
at the PWB land to solder joint interface. There
are several theories on the mechanism that creates
planar micro voids, but there is no industry
consensus on the causal mechanism for this type
of voiding. Planar micro voids are a risk for
reliability failures.
Kirkendall voids are created at the interface of two
dissimilar metals at higher temperatures. In the
case of solder attachments, at the pad to joint
intermetallic layer. They are not due to the reflow
process; Kirkendall voids are created by electro-
migration in assemblies that spend large amounts
of time above 100ºC. There is currently
conflicting evidence whether Kirkendall voids are
a reliability risk or not.
REWORK
Due to the high temperatures associated with lead
free reflow, it is recommended that this
component not be reused if rework becomes
necessary. The Dual Power56 should be removed
from the PWB with hot air. After removal, the
Dual Power56 should be discarded. The solder
remnants should be removed from the pad with a
solder vacuum or solder wick, the pads cleaned
and new paste printed with a mini stencil.
Localized hot air can then be applied to reflow the
solder and make the joint. Due to the thermal
performance of this component, and the typical
high performance PWB it will be mounted on,
quite a bit of heat energy will be necessary.
Heating of the PWB may be helpful for the rework
process.
BOARD LEVEL RELIABILITY
As mentioned previously, per JDC-STD-001D a
solder fillet is not required on the side of the lead
for this package. But it has been found through
modeling and temperature cycling that a solder
fillet on the lead end can improve reliability. An
improvement of 20% can be expected with this
fillet. It has also been found that the 20%
reliability enhancement is attained even when the
fillet only wets halfway up the side of the lead.
The customer can expect to create reliability
enhancing solder fillets through proper process
design and control.
As part of the standard reliability testing this
package was temperature cycled from -10 to 100C.
There could be no failures in the sample set at
1000 cycles to pass the test.
WORKS CITED
[1] Aspandiar, Raiyo, “Voids in Solder Joints,”
SMTA Northwest Chapter Meeting,
September 21, 2005, Intel Corporation
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