Hi Ioan,

We have seen one or more things cause this problem.

1. The part in the hole lacking any stand-off height. i.e., a molded
capacitor with the meniscus of the overcoat sticking down into the top of
the hole. If this problem only shows up on the vias, then this is ruled
out.
2. Contamination on the lead in the hole or in the hole wall itself
3. Pin-holes in the sidewall of the hole, will allow moisture to collect
along the fibers internal to the board. When you wavem the moisture turns
to steam and "explodes," producing a bubble of solder, much like blowing a
bubble with bubble gum, on one side of the board. I have usually seem this
on the bottom, rather than on the top side.

If number 3 is your problem, baking the boards prior to wave may solve the
problem. However, as [log in to unmask] said in his message, you probably
have underplated via holes. What is the diameter of the vias and how thick
is the board?  If this is anything like a high rel product, you may need to
reject the boards and return to vendor.

Good luck,

Charlie B.






"Tempea, Ioan" <[log in to unmask]> on 07/14/99 12:28:23 PM

Please respond to "TechNet E-Mail Forum." <[log in to unmask]>; Please respond
      to "Tempea, Ioan" <[log in to unmask]>



 To:      [log in to unmask]

 cc:      (bcc: Charles Barker/US/I-O INC)



 Subject: [TN] Sloder bubbles on the VIAs









Hi,

now that the problem with the blistering solder mask is fixed ( we sent the
boards back since backing them was of no use), I have another one.

Some of our assemblies have a high density of VIAs. On these products,
pretty often we get after wave some solder bubbles over the VIAs, some of
them exploded, like degassing. Since on some we see the same bubbling even
on the fiducials, I wonder if the humidity is the only one to blame, I even
wonder if there's any issue related to humidity at all.

So, what could it be? Incompatibility between flux and solder sounds
possible?

I would appreciate any input,

Ioan