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Delamination and its
Countermeasures
November 5, 2010
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Outline
Delamination Defined
Factors Attributed to Delamination in PCB
PCB Design
Material
Process
Case Study
Delamination Defined
IPC-A-600G
A separation between plies within a base material,
between a material and conductive foil, or any other
planar separations within a printed board.
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Factors Attributed to Delamination
PCB Design
Different PCB circuitry designs have different resin
content requirements which depend on the amount of
residual copper. There must be sufficient resin
formation between the glass fabric and the copper to
ensure bonding strength.
Glass stop is an indicator of insufficient amount of
resin wherein the glass fabric is already touching the
copper layer.
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Action: Use a prepreg style
or construction which can
provide more surface resin
and better flow.
Factors Attributed to Delamination
Material
Selection
Choosing the appropriate materials to be used
according to its specific thermal processing
requirements is very important in preventing future
delamination problems.
For lead-free materials, certain properties must be
specified for better performance and reliability, such as
Tg, z-axis CTE, Td and time to delamination.
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Action: Consultation between the supplier and the user
regarding the most suitable material for user’s
specifications and requirements and qualification of the
materials in user’s processes is a must.
Factors Attributed to Delamination
Material
Quality
Another possible cause of delamination is the
presence of foreign materials or contaminants, such as
oil, grease, etc. These contaminants may weaken the
bonding strength between interfaces and initiate
delamination when subjected to thermal processes.
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Action: Stringent prevention and control of entry of
these contaminants in the process work areas; and in
the raw materials being processed
Dust-free and clean working environment
Strict incoming material quality control & inspection
Factors Attributed to Delamination
Process
Oxide Treatment
The objective of this process is to chemically prepare
the surface of the copper to improve adhesion. If the
surface treatment is not optimized, the bond link
between the interface of the oxide layer and the
prepreg will be weak and will result to delamination.
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Action: Use the appropriate oxide
treatment for different PCB types
(e.g. epoxy or polyimide).
Use the right amount of
chemicals or substances.
Ensure adequate cleaning and
rinsing to avoid any unwanted materials.
Factors Attributed to Delamination
Process
Pressing / Lamination
Poor or inefficient pressing or lamination process could
also cause delamination because the material may not
be fully cured and its components have not completely
bonded.
Several properties affected if lamination process is not
good are:
Low Tg (Undercure)
Poor Peel Strength
Poor Wetting
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Action: Use the correct and appropriate press cycles
during pressing or lamination based on recommended
process guidelines of the material being used.
Factors Attributed to Delamination
Process
Handling & Storage
Improper handling, packaging and storage of PCBs
could lead to delamination due to its high sensitivity
towards moisture. The absorbed moisture when
heated at high processing temperatures will result to
an increase in its vapor pressure causing the PCB to
delaminate.
※ Make sure that the packaging is intact and stored in
a cool and dry place, with a humidity of at least 65%.
※ Avoid rapid fall in the temperature because it
causes condensation.
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Action: Heat conditioning or pre-baking of PCBs to reduce
the moisture into an acceptable minimum.
Case Study
Delamination was detected after 1X solder dip test at
288oC for 10 sec.
6-layer Board Construction
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Case Study
Tg Test Results by DSC (IPC TM-650 2.4.25C)
Material Tg Specification: Minimum 140oC
Note: The Tg value of the board increased after baking
at 180oC for 2 hours.
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Case Study
Solder Dip Test at 288oC for 10 sec
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Condition Result
As ReceivedDelamination
after 1X
Baked at 150oC
for 4hrs
Delamination
after 2X
Baked at 180oC
for 2 hrs
No delamination
after 6X
Case Study
Cross-section Analysis (After Solder Dip Test)
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Case Study
Dielectric Thickness Verification
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Case Study
Dielectric Thickness Verification
Note:
(1) The dielectric thickness of L1/L2 and L5/L6 is less
than the thickness of the 2116 glass fabric.
(2) Glass stop or glass fabric touching the inner layer
copper is apparent on the prepreg layers, L1/L2 and
L5/L6.
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Case Study
Press Profile Verification
Note: The maximum product temperature reached is
only 150oC which too low than what is expected.
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Case Study
Findings
DSC-Tg test result for as received condition indicates
that the sample is under-cured. Tg value is lower than
expected. Delamination occurred on prepreg layer
L5/L6 on this sample just after 1 cycle of solder dip
test (288°C/10 sec).
After baking the sample at 150°C for 4 hours, Tg value
increased but still low. Delamination also occurred
after 2 cycles of solder dip test.
After baking the sample at 180°C for 2 hours, Tg test
result indicated full-cured state. It reached its desired
Tg value with ∆Tg of less than 5°C. No delamination
occurred even after 6 cycles of solder dip test.
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Case Study
Findings
The dielectric thickness of prepreg layers L1/L2 and
L5/L6 is less than that of the thickness of the glass
fabric alone, thereby causing glass stop. These layers
will not have sufficient amount of resin formation
between the glass fabric and inner layer copper which
lessen the bonding strength between them and will
eventually delaminate after subjecting to thermal
stress.
Based from the press profile, the maximum product
temperature only reached around150°C. It did not
attain the required curing temperature for this material
that resulted to under-cured state of the board.
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Case Study
Recommendations
Use 2-ply 2116 prepreg instead of 1-ply to promote
sufficient butter coating between the glass fabric and
inner-layer copper interface, since the inner-layer uses
2 oz copper foil.
To ensure full-cure state, this material should be cured
at 170oC for at least 60 minutes based on the
recommended processing guidelines.
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