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Subject:
From:
Werner Engelmaier <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Werner Engelmaier <[log in to unmask]>
Date:
Sat, 7 Nov 2009 17:43:59 -0500
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text/plain (549 lines)
 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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