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September 2005

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Subject:
From:
"Stadem, Richard" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Stadem, Richard
Date:
Wed, 14 Sep 2005 10:17:55 -0500
Content-Type:
text/plain
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text/plain (170 lines)
Steve,
Now that you have probably identified the root cause of the bumps, going
back to your original question, "should I worry about these bumps?"
I would hazard a guess that you should worry about them.
It depends though, on whether there will be problems if the components
are not sitting flat on the lands. There will be a loss of surface
contact on the components that have exposed pads on the bottom that are
meant to be soldered flat for grounding and cooling purposes. And it
appears that many of the chip caps/resistors will not be sitting on a
flat pad either, which could contribute to tombstoning, skewing, and
other problems. If there are any via-in-pad BGA pads they will most
likely have a multitude of voids and other issues, and so on. I do not
know enough about the rest of the board to tell you if this is going to
be a problem or not, but these are things you may wish to consider. On
the other hand there should be less entrapped flux under the parts.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: Wednesday, September 14, 2005 9:57 AM
To: [log in to unmask]
Subject: Re: [TN] [OT]...sorta RE: [TN] raised vias...I did a "Okie"
cross-section

You're right Dewey. Geeze, always correcting me...

I shoulda' said; I did a "Okie-dokie" Okie cross-section, huh?

Speaking of which, I went back it at again this morning for a bit.
Went deeper and deeper, and the width of the hole in the via did not
change much, which tells me that I was pretty much in the center of the
via....and as was commented earlier, they did a heck of a job plating
the walls of the vias...that's some thick walls of copper.

I got to a point where I could start seeing the back wall of the hole,
because some of the resin was coming out of the hole from the gentle
scraping I was doing with the exacto knife, and yes, now I believe that
is pre-preg resin coming up through the blind via hole during lamination
to the thick copper core.

You can see my latest image at:

http://www.stevezeva.homestead.com/files/Cross_Section.jpg

This is a image that was taken from our SmartScope Flash system at
somewhere around 200 magnification.

Now comes the big question, are the bumps a reliability issue? I did see
some open/insufficient solder defects in the first build of these
boards.
We
touched things up for the most part, before I knew what was causing the
defects.
I can compensate for the insufficient  solder problems probably by
getting a thicker stencil, so should I worry about these bumps?

-Steve-



|---------+------------------------------->
|         |           "Whittaker, Dewey   |
|         |           (AZ75)"             |
|         |           <Dewey.Whittaker@HON|
|         |           EYWELL.COM>         |
|         |           Sent by: TechNet    |
|         |           <[log in to unmask]>   |
|         |                               |
|         |                               |
|         |           09/14/2005 08:38 AM |
|         |           Please respond to   |
|         |           TechNet E-Mail Forum|
|         |           <[log in to unmask]>;  |
|         |           Please respond to   |
|         |           "Whittaker, Dewey   |
|         |           (AZ75)"             |
|         |           <Dewey.Whittaker@HON|
|         |           EYWELL.COM>         |
|         |                               |
|---------+------------------------------->
 
>-----------------------------------------------------------------------
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  |
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  |       To:       [log in to unmask]@SMTP@Exchange
|
  |       cc:       (bcc: Stephen R Gregory/LABARGE)
|
  |       Subject:  Re: [TN] [OT] RE: [TN] raised vias...I did a "Okie"
cross-section                            |
 
>-----------------------------------------------------------------------
---------------------------------------|



I is a half-way measure. Doakie completes the affirmation.
Dewey

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Craig Cullum
Sent: Wednesday, September 14, 2005 5:55 AM
To: [log in to unmask]
Subject: [TN] [OT] RE: [TN] raised vias...I did a "Okie" cross-section

OK, could someone explain to me what "Okie" means please?

TIA

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