Hi Peter,
about 'battery effect' read this: http://www.circuitree.com/ct/cda/articleinformation/features/bnp__features__item/0,2133,17528,00.html
Corners=greatest distance to neutral=biggest movement increment=biggest stress.
Corners=highest cooling gradient=solidify before centre=more stress when the middle contracts
Just an idea
Ingemar
-----Original Message-----
From: [log in to unmask] [mailto:[log in to unmask]]
Sent: den 29 mars 2001 10:29
To: Ingemar Hernefjord (EMW)
Subject: RE: [TN] BGA crack pic
Ingemar, or anybody,
Can you tell me more about Biunnos's battery effect?
FYI, we've had some horrible-looking BGA solder joints, and not just in the
corners - mal-formed, very coarse granulation, cracks at ball/solder land
interface and signs of very poor reflow and bad wetting. The cause of much
of this is insufficient heat, but it may just as likely have happened at
the wave soldering process to attach the connectors as during convection
reflow. I guess someone omitted to think about a Wave Solder profile as
including BGA needs, and the solder joints only partly reflowed.
Problems with the corner balls seems to be a combination of creep fatigue
and vibration fatigue. These stresses tend to concentrate on BGA corners
first and work their way inwards to the centre. Which sadist invented BGA's
anyway, and why can't they have more ground clearance? They're still much
lower than many other components used on the rest of the board, and more
clearance would make life a lot easier. It would probably lead to greater
solder joint reliability as well.
BTW the pictures are Rudolph Yu's, not mine, but they are interesting.
Pete Duncan
"Ingemar Hernefjord (EMW)"
<[log in to unmask] To: "'TechNet E-Mail Forum.'" <[log in to unmask]>,
icsson.se> "[log in to unmask]" <[log in to unmask]>
cc:
03/29/01 02:40 PM Subject: RE: [TN] BGA crack pic
Peter,
it's strange with those corner ball problems. We have seen same. Somebody
at TN, forgot who, had the idea that wide traces to ground or power, traces
on top speaking, will act as kind of heatsinking and you'll get some lower
than average temp exposure to those balls. In our case, the cracks didn't
occur at the BGA interace but at the PWB side. Your pictures are
interesting to many I guess, but what about the heatsinking theory? Other
go more for Biunno's battery effect.
The okie man, being head guru (at least best in show, he-he) at TN now, has
the answer already?
Ingemar
-----Original Message-----
From: <Peter George Duncan> [mailto:[log in to unmask]]
Sent: den 29 mars 2001 08:06
To: [log in to unmask]
Subject: Re: [TN] BGA crack pic
I noticed the big fat track too, but as it runs right through the ball next
door, and that ball is said to be OK, I took it that it had no effect on
our faulty friend. I asked Rudolph if he had any other microsection
pictures of the surrounding balls for comparison, in case this is another
example of BGA's 'shady tree' effect, as I call it, i.e. the balls sitting
under such a large parasol don't get the heat they need to reflow properly.
Best regs
Pete Duncan
"Stephen R.
Gregory" To: [log in to unmask]
<SteveZeva@AO cc:
L.COM> Subject: Re: [TN] BGA crack
pic
Sent by:
TechNet
<[log in to unmask]
ORG>
03/29/01
11:20 AM
Please
respond to
"TechNet
E-Mail
Forum.";
Please
respond to
SteveZeva
Rudolph and everybody,
Go to:
http://www.xdrive.com/share/985835366039lhSi4tEHHweAj9vYGZA6
Good pictures Rudolph! Only thing I notice right away is that big fat trace
next to the ball that's failing...is the same pattern with this device on
the
other boards that you say uses this same asic?
-Steve Gregory-
<< Steve:
Thanks for putting this up for me. So you will let me know the URL
address?
Thanks again
Werner, Peter, Hector:
Thanks for the inputs!!
Rudolph >>
---------------------------------------------------------------------------------
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
---------------------------------------------------------------------------------
---------------------------------------------------------------------------------
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
---------------------------------------------------------------------------------
|
