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August 2007

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From:
Dwight Mattix <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Dwight Mattix <[log in to unmask]>
Date:
Fri, 31 Aug 2007 15:45:25 -0700
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shape of the uVia in x-section matters greatly.

As the finished uVia hole wall moves from a top/bottom taper (top being 
larger finished diameter) and approaches the vertical then solder voiding 
increases. As the finished uVia hole wall passes vertical and the top of 
the via opening develops an overhang effect then voiding becomes unavoidable.

... and yes, I'll take the Friday extra points for that pun.

  At 10:14 AM 8/31/2007, Bev Christian wrote:
>Other things to consider:
>1) How clean are the vias (trapped plating salts)?
>2) The smaller the VIP, the smaller the voids
>3) Two passes of the squeegee with the paste can jam more paste down
>into the vias (of course need to have good gasketing of the stencil to
>the board)
>4) We have found somewhat less voiding with a thinner stencil, but there
>are limit to this because of the requirements of different types of
>components.
>Bev
>RIM
>
>-----Original Message-----
>From: TechNet [mailto:[log in to unmask]] On Behalf Of Joe Macko
>Sent: Friday, August 31, 2007 12:53 PM
>To: [log in to unmask]
>Subject: Re: [TN] vOID IN Micro BGA
>
>I will 2nd that. I have experienced a lot of voiding issues when there
>are VIPs on uBGAs as well as other BGAs. Often the VIPs are the same
>size whether they are located in a uBGA pad or a larger say 25 mil BGA
>pad and consequently, its impact is significant. I am trying to get the
>design group to always plug and cap all VIPs so this does not become an
>issue.
>
>One work around is to use a 2 mil stencil and paste/reflow the side of
>the board with this issue prior to populating any side of the board! The
>2 mils of paste helps fill the VIPs as long as they are not too big.
>Adding an additional reflow to a non-populated board should not be an
>issue but needs to be verified.
>
>Good luck,
>- Joe
>
>-----Original Message-----
>From: TechNet [mailto:[log in to unmask]] On Behalf Of Vladimir Igoshev
>Sent: Friday, August 31, 2007 9:04 AM
>To: [log in to unmask]
>Subject: Re: [TN] vOID IN Micro BGA
>
>The presence of vias in the pads causes it. Mind, though, that even such
>large voids might not affect a long time reliability of the joints.
>
>Regards,
>
>Vladimir
>
>-----Original Message-----
>From: TechNet [mailto:[log in to unmask]] On Behalf Of shankar rao
>Sent: Friday, August 31, 2007 11:49 AM
>To: [log in to unmask]
>Subject: [TN] vOID IN Micro BGA
>
>Dear All,
>
>   We are getting Large voids  in Micro BGA  on someof the pads having
>PTH/via  (greater than 40% in dia) after reflow soldering in one of our
>multi layer PCB. We are using ROHS paste and ROHS component.  Can I know
>what may be the reason for  these voids
>
>   Regards
>
>   SHANKAR
>
>
>K. Shankar Rao
>
>---------------------------------
>  Unlimited freedom, unlimited storage. Get it now
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