Ryu,
A few more things to consider here:
- Board handling: Are the BGAs near the edge of the board where someone
holding the board with their thumbs over the top and their fingertips
underneath it, would apply high board flex stresses to the package?
Common especially near ejector latches.
-Board flexion in ATE fixtures or depanelization & breakaway tab
processes
- Post Ass'y processes: including the insertion of nearby PEMS, ejector
latches, pressfit connectors, metal shields, opto transceivers, etc.
-Mounting of daughterboards around this site, or near it on the opposite
side of the board
- Is the heatsink installation assembly process for these BGAs well
controlled?
-Are the same parts doing OK elsewhere on the board or on other
assemblies - or do they all have the same issue?
Agree with other postings that the 5DX probably won't catch this.
Depending upon the visibility of the joint, the size of the separation,
and the skill of the operator, an ERSA scope might.
Sometimes you have a fighting chance seeing that package interface using
a small first-surface mirror - like the Metrons, with a beveled edge.
You can bevel the edge yourself on a sheet of fine sandpaper. (Note -
This'll make the edge very thin and fragile; it's easily chipped.)
Illuminate with fiber optics, and under an inspection microscope,
carefully inspect the joints while very gently lifting and pressing at
the corners. You'll need to grow a third hand to do this.
Bruce Tostevin
Benchmark Electronics
Hudson, New Hampshire
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Rudolph yu
Sent: Friday, September 15, 2006 2:22 PM
To: [log in to unmask]
Subject: [TN] Need help on a Dye & Pry test result
Recently I asked an outside lab to perform the dye & pry test on couple
failure assemblies. The heatsink was not removed from the PBGA prior to
the
dye application.
According to the result and pictures, the corner pads of the BGA
package
from both units were covered by the dye completely . An indication that
a
seperation was formed between the BGA package's pads and its original
solder
balls at that one corner after the SMT process.
Have anyone of you experienced this kind of defects in the past and what
could be the root cause of this phenomena? ( Poor plating from the IC
manufacturer? SMT reflow profile? PCB warpage? )
I have been in the industry for 10 years and have never seen thing like
this. Is it common??
Thanks
Ryu
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