Laminate stack up
• A layer of uncured prepreg is placed on each
• Outer cores with the internal layers patterned
are laid up in alignment jig.
• Layers are laminated under heat and pressure.
• Laminate is now a single unified structure
Via holes are drilled
• Precision tungsten carbide drill bits are used to
drill holes where needed.
• Drilling results in a damaged layer that must be
removed by etching.
Dye & Pry Testing
• This is a quick/inexpensive way to look for
cracked or non-wetted BGA joints.
• Allows for simultaneous inspection of all of
the joints at once.
• Materials and equipment needed are
Dye & Pry Test Procedure
• Cut out device to be tested from the PCB
• Clean flux from under device and bake dry
• Immerse part in Dykem Red fluid under
• Shake off excess dye and bake dry
• Pry off BGA using pliers and/or vise and
• Inspect for any dye on separated joints
• When the assembly is temperature or power
cycled the different materials in the attach want
to expand/contract according to their CTE’s.
• The attach material is (usually) the weakest
point in the assembly so it is expected to absorb
the stresses of thermal mismatch by yielding in
• The amount of creep an attach can endure is
limited, then it will begin to crack.
Black Pad failure
This only occurs on Electroless Nickel, Immersion Gold
(ENIG) finished devices & boards:
• ENIG has come into wide use with the advent of RoHS and the lead-
• The ENIG process actually “corrodes” the top layer of the electroless
nickel-phosphorous as the gold is deposited in a displacement reaction
• This displacement reaction concentrates the phosphorous in the upper
nickel layer right under the gold, and sometimes gets out of control
• Normal electroless nickel will have 8-12% P, but black pad regions can
have up to 30% P!
• During soldering the very thin gold layer dissolves instantly leaving the
solder on top of the corroded, high P, nickel layer.
• This can result in dewetting and/or poor solder joint strength
• When the solder joints fail, the corroded nickel layer is exposed and it is
usually black in appearance; hence the name…