TECHNET Archives

March 2001

TechNet@IPC.ORG

Options: Use Monospaced Font
Show Text Part by Default
Show All Mail Headers

Message: [<< First] [< Prev] [Next >] [Last >>]
Topic: [<< First] [< Prev] [Next >] [Last >>]
Author: [<< First] [< Prev] [Next >] [Last >>]

Print Reply
Subject:
From:
"<Peter George Duncan>" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Thu, 29 Mar 2001 08:24:53 +0800
Content-Type:
text/plain
Parts/Attachments:
text/plain (136 lines)
It is the fact that it's always the 2nd last ball on the top outside row
that I find interesting. Is there no damage to the adjacent corner ball, as
this is often the first one to go in CTE differences/creep fatigue
situations? Thinking aloud for possible causes:

   Is the substrate material used for the failing boards different from the
   other products on which the BGA is used?
   Is it of a substantially different thickness?
   Is the board reaching high temperature in use, or is it subjected to
   wide temperature varience?
   Is this product subjected to greater levels of vibration and/or flexing
   in the field than other products?
   Is there a feature on or in the board that is acting as a very good
   heatsink just under or close to the failing pin? If everything else is
   heating up and this ball isn't, it's relative lack of expansion might
   pull the joint apart at its weakest point.
   Is there an inherent weakness in the BGA design or manufacture at this
   particular ball position? Is there anything different about the
   attachment point of this ball in comparison with the others if this
   device?
   Have you microsectioned any of the failed boards? Is the form of the
   solder joint significantly different from the others - shape, size,
   cleanliness, grain structure, etc?
   Have you tried doing a peel test on a sample board that hasn't failed?
   Do you suffer from Poltergeists?
   Any combination of the above?

I can't give you a definitive answer as to what causes the problem, but do
you use any underfill material with your BGA's? If not, you could try using
a urethane or epoxy underfill to support the solder joints - enough, maybe,
to hold the thing together. There are thermally conductive types of which
there are types that flow under the component and others that don't flow
under the component. I suggest you use a type that flows under the
component. Although it makes it more difficult to remove the BGA again
later, its thermal conduction properties may serve to even out any
differences in joint expansion and preserve the weak one.

Hope something here inspires some better ideas for you.

Regards

Pete Duncan
Asst Principal Engineer
ST Aerospace




                    Rudolph Yu
                    <ylt@EARTHLIN        To:     [log in to unmask]
                    K.NET>               cc:
                    Sent by:             Subject:     [TN] BGA crack- major headache
                    TechNet
                    <[log in to unmask]
                    ORG>


                    03/29/01
                    12:48 AM
                    Please
                    respond to
                    "TechNet
                    E-Mail
                    Forum.";
                    Please
                    respond to
                    Rudolph Yu






Here are the facts:

PBGA-272 balls
FR4 with HASL finishes 8 layers

The failure point always happens at the same I/O which is the 2nd last ball
of the top outmost row of the package. It is not located near the edge of
the board or any breakaway point.

Failure mode
Micro fracture found near the intermetallic layer between the BGA package
and the solder ball attached to it.

Around 0.001% of the products we built failed in the field because of this.
None of these were caught during the ICT or Functional test.

The same ASIC is also used on several other Products and have never seen an
issue like this.  Somehow this failure mode with this ASIC only occurs in
one particular product /design.


The ASIC / fab lot-related , ICT pin interference, stress by the breakaway
tab, and stencil cleanliness assumptions had already ruled out after a
controlled lot was built few weeks back.  All boards passed the tests.  But
now some boards started failing in the field.

Why the crack always happen to one single location(ball) with the same
product we built??


We have run out all the possibilities that we can think of. I hope all the
experts in TechNet can share their opinions on this.  Customer kept asking
for the root cause analysis. Right now we just cannot came up with a
reasonable one.

Thanks
Rudolph Yu

---------------------------------------------------------------------------------

Technet Mail List provided as a free service by IPC using LISTSERV 1.8d
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 delivery of Technet send the following message: SET
Technet NOMAIL
Search previous postings at: www.ipc.org > On-Line Resources & Databases >
E-mail Archives
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for
additional
information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700
ext.5315
---------------------------------------------------------------------------------

---------------------------------------------------------------------------------
Technet Mail List provided as a free service by IPC using LISTSERV 1.8d
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 delivery of Technet send the following message: SET Technet NOMAIL
Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
---------------------------------------------------------------------------------

ATOM RSS1 RSS2