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August 2009

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Subject:
From:
Guy Ramsey <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Guy Ramsey <[log in to unmask]>
Date:
Thu, 27 Aug 2009 11:50:03 -0400
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text/plain (130 lines)
Makes sense to me. If the x sections look good for thickness and the hole
drill is good you are probably right about the board outgassing.
The mask we use to hand plug vias is heat cured. A good 2 hr bake and we
don't have problems. 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Chris Mahanna
Sent: Thursday, August 27, 2009 10:47 AM
To: [log in to unmask]
Subject: Re: [TN] Via-in-pad blowing bubbles

Bob et al,
Sorry we don't have blinds outgassing.  If we see some I'll send a sample to
you. Obviously I forgot to mention the via type.  They are through vias with
single sided solder mask plug.  The plug is very deep (>75%), and maybe a
separate mask process.  Different mask?  I doubt that the board is
outgassing through the via because we've got ~1.8 mil of uniform plating.
How about incomplete plug cure?  I think that I may have some evidence of
that.

Chris

-----Original Message-----
From: Bob Willis [mailto:[log in to unmask]] 
Sent: Thursday, August 27, 2009 7:23 AM
To: 'TechNet E-Mail Forum'; Chris Mahanna
Subject: RE: [TN] Via-in-pad blowing bubbles

If you have via in a pad and its solder coated or reflowed with paste what
you describe can happen. If there is still volatile material either in the
hole, a void below the level of the solder or thin copper plating outgassing
through the copper plating can happen. Not however on gold over nickel
boards. The eruption and outgassing will be random depending on what is
there, speed of heating and how long the solder remains molten.

Just like any gassing from a plated through hole you can see a nice ball, a
balloon blow out or a sunken joint and this can be all associated with
outgassing. The classic problem with through vias is when engineers try to
fill small vias on side one reflow, then spend hours cleaning balloons off
side two before printing again.

If you simply find a sample board with the problem you describe and place it
under a microscope, fill the view with a group of pads in question. Take a
micro soldering iron and touch sample pads and wash what happens. You can
use the old oil outgassing test I have used for years to see the outgassing
from the vias on a bare board Unfortunately I don't have a via example to
show you but if you look at http://defectsdatabase.npl.co.uk and do a search
for via outgassing you will see some a video and gif animation and images.

If someone has some good examples of blind vias that are outgassing, send me
a board and I will test it and share the video on TechNet. I have tested
vias in the is way before for customers but never videoed the results.

Many thanks

Many thanks
 
Bob Willis
2 Fourth Ave, Chelmsford, Essex, CM1 4HA England
Tel: (44) 1245 351502
Fax: (44) 1245 496123
Mobile: 07860 775858
www.ASKbobwillis.com
www.SolderingStandards.com 


New Package on Package Workshops 24th November
www.ASKbobwillis.com/PoPWorkshops.pdf
PCB Design for Manufacture & Assembly Workshop 15th October
www.ASKbobwillis.com PCB Inspection & Quality Control Workshop 3rd November
www.ASKbobwillis.com/faworkshops.pdf
Book Bob's "Step by Step Failure Analysis Workshop" 4th November
www.ASKbobwillis.com/faworkshops.pdf
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Chris Mahanna
Sent: 27 August 2009 02:34
To: [log in to unmask]
Subject: [TN] Via-in-pad blowing bubbles

Hello netters-

Have we a term for vias-in-pad blowing solder ball bubbles to the point of
bridging?
Regardless, is there a unique cure for the problem?
I wonder because- how does one get just enough pressure to blow the large
bubble, but not blow-out?   Bad luck?
Or is it not that unusual, and just usually gets screened before it gets to
me?

Chris


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