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
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