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November 2009

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Subject:
From:
"David D. Hillman" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, [log in to unmask]
Date:
Fri, 6 Nov 2009 17:35:34 -0600
Content-Type:
text/plain
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text/plain (459 lines)
Hi Werner! I suspect you asked this question intentionally so I'll provide 
the answer you were expecting - the HASL process was incorrectly applied 
to the board resulting in the thin solder coating. A thin coating results 
in oxidized IMC which is nonwettable in many standard soldering processes. 


Dave Hillman
Rockwell Collins
[log in to unmask]




Werner Engelmaier <[log in to unmask]> 
Sent by: TechNet <[log in to unmask]>
11/06/2009 08:48 AM
Please respond to
TechNet E-Mail Forum <[log in to unmask]>; Please respond to
Werner Engelmaier <[log in to unmask]>


To
[log in to unmask]
cc

Subject
Re: [TN] BGA Balls






 Hi Ioan,
What is causing this is that too much solder was blown off the surface 
leaving not enough solder on top if the IMCs.
Werner

 

 

-----Original Message-----
From: Ioan Tempea <[log in to unmask]>
To: [log in to unmask]
Sent: Fri, Nov 6, 2009 9:28 am
Subject: Re: [TN] BGA Balls










Well, Bob,

Until 5 months ago I had not seen issues with HASL either, but since then 
this 
finish is the biggest issue I have ever had, for a particular product. 
Basically 
we're talking about pads with uneven SnPb thickness, especially on fine 
pitch 
parts, where the protective layer is getting so thin towards the 
extremities of 
pads that I only end up with intermetallics, that I cannot solder on. What 

causes this? Still no exact idea, although I have intensively questioned 
Technet 
and our PCB fab.

Best regards,

Ioan Tempea, ing.
Ingénieur Principal de Fabrication / Senior Manufacturing Engineer
T | 450.967.7100 ext.244
E | [log in to unmask] 
W | www.digico.cc

N'imprimer que si nécessaire - Print only if you must


-----Message d'origine-----
De : Robert Kondner [mailto:[log in to unmask]] 
Envoyé : Friday, November 06, 2009 9:02 AM
À : [log in to unmask]
Objet : Re: [TN] BGA Balls

Rex,

  ENIG seems like a finish that lot of folks love, a big reason is it is
flat.

  I must have tunnel vision because I read on this link the problems with
bad ENIG. Flat is not an issue with solder paste applied, right?

  I am using HASL and it just works so well for me. 

  Now HASL might not work for everyone but I just can not jam into my
neurons why.

  Can anyone help here?

Thanks,
Bob Kondner

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Rex Waygood
Sent: Friday, November 06, 2009 5:14 AM
To: [log in to unmask]
Subject: Re: [TN] BGA Balls

Ummm.
A few things come to mind at the moment
Humble Pie
Egg on Face
Less haste more speed
Live and learn
Etc
Shortly after the post below I decided to look at the 'posted' pcb in more
detail.
I decided to try and pry off another BGA (It's a flash part I think)
I just used my finger nail and there was a slight creaking noise and the
part flicked off (without damaging my finger nail)
Just for fun I did another.
Photo to follow from Steve.
This seems to show no wetting on the Ni on some pads (Passivated Ni?).
I couldn't believe it was a pcb problem as the customer said it was only 
the
processor that did not work.
I went back to the processor and was able to flick off some balls.
I never did like ENIG....................
Thanks again

Regards
Rex

As it is Friday feel free to make this a subject for humour!
:-)

 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Rex Waygood
Sent: 06 November 2009 08:01
To: [log in to unmask]
Subject: Re: [TN] BGA Balls

Dear All

I have a way forward with our customer following the helpful advice 
received
through TechNet and direct from some readers.
I am interested in the comments about the datasheet and as someone pointed
out there were 24 pages of errata on the data sheet but it did not include 


Note: It is recommended to apply a soldering temperature higher than 250°C
Should read
Note: It is recommended to NOT apply a soldering temperature higher than
250°C

So we are assuming they really do need 250C

Here is another lead free part from Atmel
http://www.atmel.com/dyn/resources/prod_documents/doc3438.pdf

Page 3 gives 245C max  Page 4 gives 235C peak

So I don't know how one makes assemblies containing both in mass 
production
process!

Regards
Rex




-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D.
Sent: 05 November 2009 18:59
To: [log in to unmask]
Subject: Re: [TN] BGA Balls

Hi, Werner
I could not agree with you more. The process information that is in many
component specifications is sometimes so off the wall I can't believe they
actually let it get into print. I have seen BGAs that are only available
with SAC305 solder balls, but the recommended profile is for standard 
Sn63,
and so on and so forth. Another stated that if the Sn63 BGA is soldered 
and
has any voiding whatsoever it is proof that an unleaded (hotter) profile 
was
used, and the component vendor would not be responsible for any damage 
that
occurred!

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Werner Engelmaier
Sent: Thursday, November 05, 2009 1:46 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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