To say that "via in pad" is not reliable is not backed up with any data I
have seen.  On the other hand, I have seen data from IBM that used via in
pad for many of their "ThinkPad" HDI boards in their notebook computers,
for many years that shows that it is very reliable.  The issue like so
many others is how it is applied.  The latest publication from Solectron
about "Voids in VIP Soldering for BGAs" shows that the trapping of air can
be minimized, and even when their is a void, the joint does not fail, but
it's something they want to eliminate none-the-less.  Using VIP on BGAs
may create the "void" in soldering.  If this is something you can't live
with, then a "Inset microvia" can be used, or one next to the soldering
pad but still covered with soldermask.  Proper manufactured VIP used for
SMT discreet components lands saves a lot of space and does not have any
"voids" or failure mechanisms that I know of.
Filled and capped microvias are always an option, using either conductive
or non-conductive fills.


Open via in pad is not reliable for many issues, including z-axis stress
introduced the lead attach during operating temperture exursions.

The design should be reviewed first to look into moving the via which is
generally a good option.  A conductive via fill can also be used to
produce
a flat landing site for soldering.  The cost for conditive via fill often
time outweights the cost to re-layout the package.

---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 1.8e
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
-----------------------------------------------------