Good question, Helena.
Three major reasons why delamination of the substrate is "bad" (read:
cause reliability issues) that come to mind quickly:
1. Delamination puts tremendous pressure on the z-axis of the via wall,
and will lead to separation (electrical open) between the top and bottom
portions of the via hole wall. This would leave the top layer
disconnected from the bottom layer of that particular network, or would
disconnect inner layer traces from the source via. Trace pullaway from
the via will also cause the circuit to fail.
2. Delamination puts extreme stresses on the solder joints. Flexing the
pwb material upwards from any points anchored to vias and through-hole
connections puts stress on the solder, leading to pre-mature failure due
to cracking and creep-fatigue-related solder joint failures. The void
will expand and contract with temperature cycles.
3. Delamination creates a resin void. Actually, it is the other way
around, in that delaminations are usually caused by an abcess that
begins as a resin void. In any case, an air pocket is left inside the
pwb. This can continue to expand if the assembly is thermally cycled
during its normal operation in the field, further damaging the surface
foil and via substrates that are in the area of the delamination.
4. Condensation and flux entrapment can form in the delamination,
causing electrical performance issues.
5. Delamination on high-frequency/high-impedance will disturb the
impedance of the net. This has to be carefully controlled.
6. Dielictric properties of the pwb will change and become unstable.
And lots and lots of other reasons.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Pasquito, Helena
Sent: Tuesday, September 12, 2006 11:45 AM
To: [log in to unmask]
Subject: [TN] Delamination
Hi TechNetters,
Let me ask a question; I know delamination is bad, but why? What is the
failure mode to the board when a board delaminates and would there ever
be an instance that a board that delaminates is still OK to use? This
is a Class 3 application. Yes, I know what the IPC standards say but
not real sure about the board process. Yes, I "googled" and there is a
lot of stuff out there. Maybe someone can recommend some reading
material (hopefully short and sweet and to the point).
Thanks!
Helena
Helena Pasquito
Manufacturing Skills Instructor
M/A-COM, Tyco Electronics
1011 Pawtucket Blvd., M/S 107
Lowell, MA 01853
978-442-5024
[log in to unmask]
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