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April 2010

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From:
"Post, Scott E" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Post, Scott E
Date:
Thu, 22 Apr 2010 08:31:26 -0400
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Head in pillow at the periphery can also be due to BGA and/or board
warpage.  I've dealt with two instances where this was the root cause.
Inconsistent paste print has bit us a few times too and right now I'm
dealing with one where I suspect the copper pattern on the board being
the issue.  Unfortunatly I haven't dealt with a ball in cup situation
yet that could be fixed with the reflow profile.

Scott Post 
P.O.U. 0000-001E-0CTC
2151 E. Lincoln Road 
Kokomo, Indiana    46904-9005 
765-451-2983 (Phone) 
765-451-0287 (FAX) 


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Werner Engelmaier
Sent: Wednesday, April 21, 2010 3:05 PM
To: [log in to unmask]
Subject: Re: [TN] Head in Pillow and grapping effects mitigation without
Nitrogen

 Hi Cedric,
What do you mean by 'grapping effect"?
You do not say where you find 'Head-on-Pillow' defects-they can occur at
the BGA periphery and in the BGA center and the root cause is quite
different.
HOP at the periphery is a solderability issue and certainly involves the
choice of paste/flux.
HOP in the BGA center means you do not have enough heat there to get the
solder ball to a low-viscosity liquid state-that means you need to
increase the peak reflow temperature.
One of the reasons for larger solder volumes is to achieve greater SJ
stand-off heights to improve reliability.
Werner

 


 

 

-----Original Message-----
From: Cedric ORAIN <[log in to unmask]>
To: [log in to unmask]
Sent: Wed, Apr 21, 2010 2:38 pm
Subject: [TN] Head in Pillow and grapping effects mitigation without
Nitrogen


Hello all, 

Very fine pitch BGAs (typically 0.5mm) and 0201 chips are becoming
common in our company for some months. 

We recently have to face with new defects type such as grapping effect
and head in pillow defect. 

The solder paste we use has been qualified for even smaller component
(WLP, 0.4mm pitch) but in Nitrogen atmosphere.

I'm now wondering if this solder paste is suitable with Air reflow. I'm
also wondering if a solder paste suitable in that case even exists. 

Having a look to this study from intel (link hereunder, page 31), I
found that the people from Intel are recommending a solder paste volume
larger than 2000 mil^3 as a minimum.
 
http://edc.intel.com/Download.aspx?id=3044&returnurl=/default.aspx

That is, off-course, impossible for a VFBGA (which solder paste deposit
is closer to 900mil^3) but this reading makes me feel uncomfortable. 

So the question is: is it possible to find out a solder paste which is
suitable for VFBGA assembly in Air reflow? 

If it is not against TechNet rules, have you some solder paste
references that you could advise?

Here are some additional details: ENIG PCB finition, SAC305 Alloy.

Cedric ORAIN
Technical Director
Electronic Manufacturing Services
www.inovelec-groupe.com 

PS: I'm very new and I'm also French. I wish it will not be too much for
you! Anyway, thank for being patient if I have difficulties to
understand.




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