Hello,

I have a defect that looks like delamination. One important observation
noted is that this defect is found only around PTH vias NOT component
holes. In addition, this "suspected delamination" surfaces are very flat
to touch - no bulging. I do not think it is delamination because I have
never seen delamination occurs around PTH. However, I am be wrong. This
defect appear in several areas on the board but funny observation is
that 3 out of 5 pcs of the fabricated boards have the same defect at the

same locations, around P3 and P4. The only difference is the intensity
of the defect.

This is a 8-layer design with L4 as power and L5 as ground. As such,
clearances are expected for pads not to be shorted to these
layers.However, instead of solid round clearance around the pads,
irregular shapes are found. In one of them, the clearance actually
overlap each other. The layer stackup is as follows :

---------------------------18um
      prepreg 1080+7628
 -----------------------core 0.21mm(35um/35um)
      prepreg 1080*2
 -----------------------core 0.21mm(35um/35um)
      prepreg 1080*2
 -----------------------core 0.21mm(35um/35um)
      prepreg 1080*2
 ---------------------------18um

I have seek Steve's kind assistance to download 4 pictures of the
defects. Kindly look at them. I would appreciate your opinions on :
1. If this is not delamination, what defect is it?
2. What is or are the likely cause(s)?
3. Does it has impact to reliability?

Thanking you all in advance.

Regards,
Wee Mei

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