Hi Philip,
Bellow my reply:
The balls are SAC305. The process is LF and the BGA balls see 237-245
for
30 seconds minimum. Ramps are less than 2.5 up and down.
The crack occurs catastrophically after exiting the reflow and appears
to
be the result of CTE expansion mismatch. Reuven: Pls inform the CTE XYZ
of the PCB and the component
Accordingly I have some CTE questions:
If the BGA component body is expanding/contracting quicker than the PWB,
stress would be expected at the component/ball interface: True or
False?Reuven: Yes also PCB pads copper epoxy interface during
solidification
If the PWB is expanding/contracting more than the BGA body, the cracking
would be expected at the PWB/ball interface: True of False? Reuven: Yes
also BGA balls / copper pads copper epoxy interface during
solidification
The outside rows of balls solidify first as compared to the center
balls,
and have greater natural stress with respect to mechanical forces: True
of
False?Reuven: Its depend the BA body construction so you have to check
with TC, The outside rows have shorter time to liquid and get to higher
temp and cool faster. The mechanical stress during solidification exist
on both sides of the BGA balls. You should check the coplanarity /
warpage of the BGA component and the copper balance of the PCB layout in
this area (outside and internal layers).
I would not expect the stress of CTE to snap all of the balls across the
component and this might explain why the chip doesn't fall off the
assembly
until someone "taps" it on a bench top. Reuven: how many BGAs and where
are the location on the assembly? do the failure occur only on one
location or randomly?
Best Regards
Reuven ROKAH
e mail: [log in to unmask]
-----Original Message-----
From: Phillip Bavaro [mailto:[log in to unmask]]
Sent: Friday, February 15, 2008 11:23 PM
To: Reuven Rokah
Cc: TechNet E-Mail Forum
Subject: RE: [TN] Samsung Memory BGA Failure
The balls are SAC305. The process is LF and the BGA balls see 237-245
for
30 seconds minimum. Ramps are less than 2.5 up and down.
The crack occurs catastrophically after exiting the reflow and appears
to
be the result of CTE expansion mismatch.
Accordingly I have some CTE questions:
If the BGA component body is expanding/contracting quicker than the PWB,
stress would be expected at the component/ball interface: True or False?
If the PWB is expanding/contracting more than the BGA body, the cracking
would be expected at the PWB/ball interface: True of False?
The outside rows of balls solidify first as compared to the center
balls,
and have greater natural stress with respect to mechanical forces: True
of
False?
I would not expect the stress of CTE to snap all of the balls across the
component and this might explain why the chip doesn't fall off the
assembly
until someone "taps" it on a bench top.
Phil
At 04:24 PM 2/13/2008 +0200, Reuven Rokah wrote:
> Hi Philip,
>
>The Samsung Memory BGAs are Lead free balls (is it?).
>
>Are you using Sn Pb process or lead free process?
>
>Reuven
>e mail: [log in to unmask]
>
>
>-----Original Message-----
>From: TechNet [mailto:[log in to unmask]] On Behalf Of Phillip Bavaro
>Sent: Wednesday, February 13, 2008 3:59 AM
>To: [log in to unmask]
>Subject: [TN] Samsung Memory BGA Failure
>
>I am wondering if anyone else out there has run into a problem with a
>Samsung Flash memory device (in this case, the 0.8 mm pitch, 107 pin
>sac305
>BGA) where the connections are cracking right at the interface between
>the
>pwb and ball.
>
>I had read about some Samsung BGA problems but cannot find the link to
>the
>information now.
>
>We have other BGA's on the same board without any issues. Shear
>strength
>test results are very low as well (if the flash has not already popped
>off
>by itself).
>
>I'll try to get some pictures to Steve to put up tonight. My current
>thoughts are CTE's are grossly mis-matched as we haven't found anything
>on
>the pads to account for the gross failure.
>
>Thanks in advance,
>
>Phil
>
>---------------------------------------------------
>Technet Mail List provided as a service by IPC using LISTSERV 15.0
>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
847-615-7100
>ext.2815
>-----------------------------------------------------
---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 15.0
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 847-615-7100 ext.2815
-----------------------------------------------------
|
