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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