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November 2009

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Subject:
From:
Rex Waygood <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Rex Waygood <[log in to unmask]>
Date:
Fri, 6 Nov 2009 08:00:36 +0000
Content-Type:
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text/plain (251 lines)
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

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Hansatech EMS Limited
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