That is why you never sleep! Understood.
--------------------------
Sent using BlackBerry
----- Original Message -----
From: TechNet <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Sent: Sat Nov 07 17:43:59 2009
Subject: Re: [TN] BGA Balls
Hi Inge,
I do, I do—but I just was in Casablanca.
Werner
-----Original Message-----
From: Inge <[log in to unmask]>
To: TechNet E-Mail Forum <[log in to unmask]>; Werner Engelmaier <[log in to unmask]>
Sent: Sat, Nov 7, 2009 6:11 am
Subject: Re: [TN] BGA Balls
W, do you never sleep?
/Inge
----- Original Message -----
From: "Werner Engelmaier" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Saturday, November 07, 2009 11:25 AM
Subject: Re: [TN] BGA Balls
Hi Gaby,
This is a loaded question, because of the many 'It depends.'
There are some BGAs that are thermally asymmetrically designed—particularly
those with a built-in heat sink. The faster you cool them from soldering the
more they warp; to some extent, that is also true for PCBs.
So, who to blame—see above.
The same mechanism causing your problems is at work with Pb-free soldering
causing 'pad cratering.'
Werner
-----Original Message-----
From: Gabriela <[log in to unmask]>
To: 'TechNet E-Mail Forum' <[log in to unmask]>; 'Werner Engelmaier'
<[log in to unmask]>
Sent: Sat, Nov 7, 2009 4:16 am
Subject: RE: [TN] BGA Balls
Werner,
We experienced the failure of corner solder joints sometimes and supposed
that the trigger was in the mechanical concept of the assembly.
The reflow process was OK.
Warping of the BGA or the printed circuit, electrical test stress by probes
near the corner, connectors near the BGA, were the trigger.
I thought that the separation of the solder ball occurred on the weakest
interface, which may have been on the component side.
Is this a cause for accusing the BGA manufacturer or rather the design of
the assembly and its use at the field?
Gaby
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Werner Engelmaier
Sent: Thursday, November 05, 2009 8:46 PM
To: [log in to unmask]
Subject: Re: [TN] BGA Balls
Hi Bob,
There is a lot of non-sense put force, and unfortunately, IPC no longer has
any reliability experts give workshops on reliability at APEXPO 2010.
Werner
-----Original Message-----
From: Robert Kondner <[log in to unmask]>
To: 'TechNet E-Mail Forum' <[log in to unmask]>; 'Werner Engelmaier'
<[log in to unmask]>
Sent: Wed, Nov 4, 2009 5:51 pm
Subject: RE: [TN] BGA Balls
Hi,
I recall seeing it in the temp specs on the data sheet. It did sound rather
low for SAC.
I did not see SAC305 called out, not sure what material it was. I would
have to go back and double check that data sheet but I swear I saw an above
217 for xxx seconds. I did see the 250 reccomendation and I did see the 260
+0 limit.
Bob Kondner
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Werner Engelmaier
Sent: Wednesday, November 04, 2009 4:53 PM
To: [log in to unmask]
Subject: Re: [TN] BGA Balls
Hi Bob,
Where do you get "were above the 217 minimum" from? 217 is the Solidus of
SAC solders-you cannot solder at that temperature because the Liquidus is
higher than that and alloy dependent. As an absolute minimum for reflow
[unless vapor phase] you need Liquidus+20C at the slowest heating SJ at the
BGA center.
'Verifying conductivity' is insufficient, since the latent defect
'head-on-pillow' will give you functionality in a test-and, yes, 5 C can
make the difference.
Werner
-----Original Message-----
From: Robert Kondner <[log in to unmask]>
To: [log in to unmask]
Sent: Wed, Nov 4, 2009 11:54 am
Subject: Re: [TN] BGA Balls
Rex,
Wow, what a you know what contest. :-(
They complain about a 5C difference at 250C? Hitting 245 is good IMHO, the
absolute max looks like 260. You were above the 217 minimum.
Do you have any pin test functions like JTAG or ICT to verify joint
conductivity? Testing for manufacturing defects (MDA) using execution of
application logic is difficult at best. If they really think there are
manufacturing defects (opens, short) I would go for something to verify
connectivity parts. If there are many manufacturing defects then you have a
process problem. If there are none then it is an application problem.
Bob Kondner
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Rex Waygood
Sent: Wednesday, November 04, 2009 11:36 AM
To: [log in to unmask]
Subject: [TN] BGA Balls
We have built a batch of pcbs for a customer who supplied the pcbs. They
are 2mm thick 6 layer with 0.2mm vias and ENIG finish. None work fully,
they work intermittently at best.
The customer was suspicious that we had not reflowed the BGAs correctly.
Our under BGA temp on a similar pcb is 245C (We now have some samples to
profile correctly)
The customer is suspicious due to the comment on page 753
http://www.atmel.com/dyn/resources/prod_documents/doc6221.pdf
<http://www.atmel.com/dyn/resources/prod_documents/doc6221.pdf> where
it states a min of 250C
Close x-ray evaluation of the BGAs showed tear dropping along tracks,
uniform balls, everything looked tickety boo.
We offered to remove a BGA to see what was happening underneath.
2 corners showed a similar issue with the ball where it separated from
the BGA rather than the pcb.
The removal technique was to use a PDR IR rework station, under board
heating to bring topside pcb temp to 170C and then a lead free reflow
profile to bring the device up to reflow, manual removal.
I didn't have dye for dye and pry so thought this might show if there
was an ENIG problem.
I was surprised by the almost complete removal of ball at the device and
lack of evidence of solder.
Was this just caused by my investigation processes?
Was the ball device interface broken which prevented it from melting the
ball?
Any other clues?
Thanks
Rex
Hopefully Steve has received the images (sorry about the size!)
Rex Waygood
Technical Manager
Hansatech EMS provides value manufacturing through engineering and
quality
________________________________
Hansatech EMS Limited
Benson Road
Nuffield Industrial Estate
Poole
Dorset BH17 0RY
United Kingdom
Tel:
Fax:
DDI: +44 (0)1202 338200
+44 (0)1202 338202
+44 (0)1202 338222
[log in to unmask]
www.HansatechEMS.com <http://www.hansatechems.com/>
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