George,
I am not an experienced metallurgist,
But I agree with you that the mechanical stress for solder balls is very
common on the Ball/ component side.
I suppose that this occurs mainly because the upper joint is solder mask
defined, and the lower joint is usually not solder mask defined,
encapsulating the circuit pad with the solder of the ball.
But in our example, both upper and lower pads are of the same size, and the
solder ball/circuit joint is also solder mask defined.
In the end in this configuration, there is no general rule, and the
strenghth of the solder joints is depending on all processes which may
influence the weakest joint.
Gaby
----- Original Message -----
From: "Wenger, George M." <[log in to unmask]>
To: <[log in to unmask]>
Sent: Saturday, February 16, 2008 9:58 AM
Subject: Re: [TN] Samsung Memory BGA Failure
I've been reading all of the TN emails which cover a wide
Phil,
I've been reading all of the TN emails which cover a wide range of
speculation from brittle fracture to poor solder joint because the
temperature was too low. All of the speculations are good but they are
based on what contributors think they see in the cross section that is
posted on Steve's site. I've been struggling to understand what is
really happening but I feel the quality of the cross section isn't good
enough to be able to know what the defect is. I can't see if there is
IMC and if there is I can't see if the separation occurred between the
IMC and Ni plating or between the IMC and bulk solder or within the IMC.
What I see in the photomicrograph is a BGA solder ball that appears to
be attached to a solder mask defined pad on the package that is
approximately 10% smaller in diameter than the solder mask defined pad
on the PCB. If you had formed a good solder joint to the PCB and there
was mechanical stress on the solder joint I would have expected the
separation to have been at the interface to the package rather than at
the PCB interface. If you like I have access to a world class
metallographer and I'm sure if you sent me the cross section it would
only take him a couple of minutes to re-polish the cross section and I
could provide you with photomicrographs of the re-polished cross
section.
Regards,
George
George M. Wenger
Andrew Wireless Solutions
Senior Principal FMA / Reliability Engineer
40 Technology Drive, Warren, NJ 07059
(908) 546-4531 [Office] (732) 309-8964 [Cell]
[log in to unmask]
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: Friday, February 15, 2008 9:58 AM
To: [log in to unmask]
Subject: Re: [TN] Samsung Memory BGA Failure
Hi Phil!
Got the picture you sent yesterday afternoon posted now, it's at:
http://stevezeva.homestead.com/files/LP_BGA_Crack.jpg
Man, fractured clean through! Do all the fractures look like that?
Steve
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Phillip Bavaro
Sent: Tuesday, February 12, 2008 7:59 PM
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
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