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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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