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June 2009

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Subject:
From:
Vladimir Igoshev <[log in to unmask]>
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Date:
Sat, 13 Jun 2009 22:10:07 +0000
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At least I'm in a "better position", as get involved  as a consultant :-)



Vladimir

SENTEC

SENTEC

11 Canadian Road, Unit 7.

Scarborough, ON M1R 5G1

Tel: (416) 899-1882

Fax: (905) 882-8812

www.sentec.ca





-----Original Message-----

From: Gabriela <[log in to unmask]>



Date: Sun, 14 Jun 2009 00:01:07 

To: <[log in to unmask]>; <[log in to unmask]>

Subject: RE: [TN] Corner ball pad cratering





We had similar problems.

As you too, I saw it much more in ROHS applications.

And why not be frank-I will tell you what happened next:

Production did not  believe total loss, BGA's went through re-reflow- for

nothing ( oh, sorry, more cratered pads), removal (more cratered pads),

Lifted pads after removal, Pad repair on those we SAW, NEW BGA soldering,

failure again,due to pad/via open because the lifted pads separated from the

connectors (seen by X-ray).

Blabbering? Because I was and am FURIOUS!!!!!

SAC!!phui!

Gaby



-----Original Message-----

From: TechNet [mailto:[log in to unmask]] On Behalf Of Vladimir Igoshev

Sent: Friday, June 12, 2009 9:51 PM

To: [log in to unmask]

Subject: Re: [TN] Corner ball pad cratering



I wouldn't be surprise if some of the joints are also partially cracked

right after re-flow. That is what I saw in the case I mentioned yesterday.



In fact it was rather unusual to see partially craterred pads under

partially cracked balls.



As far as I know, my customer still tries to convince their CM to change the

re-flow profile (the cooling rate they used was way too high, but they've

never admitted that).



Regards,



Vladimir

SENTEC

SENTEC

11 Canadian Road, Unit 7.

Scarborough, ON M1R 5G1

Tel: (416) 899-1882

Fax: (905) 882-8812

www.sentec.ca





-----Original Message-----

From: Bev Christian <[log in to unmask]>



Date:         Fri, 12 Jun 2009 13:35:13 

To: <[log in to unmask]>

Subject: Re: [TN] Corner ball pad cratering





Chris,

We do extensive cross-sectioning to qualify any new reflow process and

all new Blackberry models. I have never, ever seen a pad cratering event

at this juncture - only after dropping during testing or from field

returns.

Bev



-----Original Message-----

From: TechNet [mailto:[log in to unmask]] On Behalf Of Chris Mahanna

Sent: Friday, June 12, 2009 1:26 PM

To: [log in to unmask]

Subject: Re: [TN] Corner ball pad cratering



Genny and Bev,

Out of curiosity- are you sure that the cratering was not: induced

thermally (during reflow cool down), but did not manifest itself as a

problem until other mechanics came into play?

It just seems like that would be more common.

Chris



Chris Mahanna

Robisan Laboratory







-----Original Message-----

From: TechNet [mailto:[log in to unmask]] On Behalf Of Genny Gibbard

Sent: Friday, June 12, 2009 12:12 PM

To: [log in to unmask]

Subject: Re: [TN] Corner ball pad cratering



As always, Steve, you are a wealth of information.  That article is

perfect, thank you.  This seems to mirror what Amol said about doing a

1/4 of the length.  This article said to do an L shaped bead 2-6 balls

along each corner side.

Here are some photos to post.  Would you oblige?

BGA is 40mm per side.  PCB is ~1 ft sq.  A little bigger than what is

found in the typical blackberry, I think... Ball pitch is 1.27mm.

We believe the cause is mechanical, not thermal.

Thanks everyone.



Genny



-----Original Message-----

From: Steve Gregory [mailto:[log in to unmask]]

Sent: June 12, 2009 6:35 AM

To: TechNet E-Mail Forum; Genny Gibbard

Subject: RE: [TN] Corner ball pad cratering



Morning Genny,



Since you said you were going to look at corner bonding, here is a

really good article (if you haven't seen it already) that Michael

Kochanowski from Intel and Brian Toleno from Henkel did about it:



http://www.trafalgar2.com/documents/Technical_Articles/6.09-kochanowski.

pdf



Steve



-----Original Message-----

From: TechNet [mailto:[log in to unmask]] On Behalf Of Genny Gibbard

Sent: Thursday, June 11, 2009 3:10 PM

To: [log in to unmask]

Subject: [TN] Corner ball pad cratering



Hello all,

If you have identified a BGA with corner ball pad cratering, what would

be your suggestions to correct this condition?

Our thoughts:

1.  We plan to evaluate our handling processes to reduce/remove

excessive flex/strain occurring around this part 2.  We plan to evaluate

corner bonding or underfilling for the BGA.



Which do you feel would be the best direction to go?  Do you have other

suggestions?

Thanks in advance for all your help



Genny



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