One issue to watch out for in purchase of dummy BGAs for reliability
testing is that the size / presence of the die in the BGA can
significantly effect the solder joint life. We found (to our dismay)
that most dummy parts HAVE NO DIE. Even those that said they did in
fact when we examined parts we found the die had been "deleted" by
vendor as "non-functional" (in an electrical sense in the dummy parts it
is as the "daisy chain" is done by the interposer).
If thermal cycling is part of reliability testing, I suggest you get
parts with die of size you'll be using. And if you find a source LET ME
KNOW!!!!!
Any sources known to anyone else would be GREATLY appreciated.
Jim
===============================
Jim Maguire
Senior Principal Engineer
Boeing Defense & Space Group
PO Box 3999 M/S 3W-97
Seattle, WA 98124-2499
Phone (206)657-9063 Fax 657-8903
Email: [log in to unmask]
================================
> ----------
> From: Charles Barker[SMTP:[log in to unmask]]
> Reply To: TechNet Mail Forum.;[log in to unmask]
> Sent: Tuesday, October 14, 1997 1:41 PM
> To: [log in to unmask]
> Subject: [TECHNET] Assy: BGA stuff
>
> Charles Barker@IO-US
> 10/14/97 03:41 PM
>
> Perhaps Friday was not a good time to put out such an extensive
> questionaire, so I am re-posting it today.
>
> I have received several answers to question #1 and one partial answer
> to
> the other seven.
>
> Four or five folks have asked for a copy of the summary of the
> feedback I
> get.
>
> I sure would appreciate some more data to summarize!
>
> TIA,
>
> Charlie B.
>
> ---------------------- Forwarded by Charles Barker/IO-US on 10/14/97
> 03:31
> PM ---------------------------
>
> To: [log in to unmask]
> cc:
> Subject: Assy: BGA, dummies, pad finishes, stencils, profiles, SM
> opening
> size, Bd material
>
> We are about to get into processing boards with BGA devices. We will
> more
> than likely have products which will require a SMT reflow - wash - SMT
> reflow - wash - through hole soldering (either selective wave or hand)
> -
> wash, series of process steps.
>
> If our design engineers don't change their minds, the first package we
> will
> have to deal with will be a 432-ball plastic Xilinx critter with balls
> 1.27mm (0.050") apart. Once they are happy with this design, I am sure
> we
> will be looking a micro-BGA, etc. Our present board finish is LPI
> SMOBC
> with hot air level. Bd material is regular FR-4.
>
> The products we produce are used in the field all over the world in
> all
> temps and climates. This first BGA product will be speced and temp
> cycled
> from -10 deg C to +55 deg C. Probable future units will have to
> handle
> from -50 deg C to +85 deg C.
>
> For those of you who have experience with BGA's, help! We don't want
> to
> totally re-invent the wheel!
>
> 1. Do you know of a source for dummy practice parts other than
> TopLine?
> They don't have this particular size.
>
> 2. Comments about OSP pad finishes? Will they tolerate all the process
> steps and still protect against oxidation at the latter stages? It
> could be
> that the process may stretch out over several days. e.g., reflow and
> wash
> day one, second reflow and wash on day two or three, and then final
> through
> hole and wash on day four or five. Anything could stretch out the
> over-all
> process time such as weekends and holidays.
>
> 3. What about other pad finishes? Palladium, Gold, Plain old hasl?
>
> 4. What stencil thickness for BGA? Do you find .006" sufficient? Have
> you
> experienced bridging with .008"?
>
> 5. Did you find that your oven profile changed drastically from that
> used
> for boards with, say, 200+ pin leaded devices?
>
> 6. What about solder mask defined pad areas as opposed to SM opening
> bigger
> than the pads?
>
> 7. With this large of a device (40mm x 40mm) I am concerned about CTE
> mismatch over the operating temp range specified as well as the
> process
> temp range to which it will be exposed. What board materials would
> you
> recommend? Would you spec one of the higher Tg materials? Why? I
> will
> need to provide cost justification for wanting this more expensive and
> for
> some shops, more difficult to process, material.
>
> 8. What are your responses to the questions above for Micro-BGA?
>
> For those interested, I will pull together a summary of my findings.
>
> TIA
>
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