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June 2009

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From:
"David D. Hillman" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, [log in to unmask]
Date:
Wed, 3 Jun 2009 16:26:13 -0500
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Hi Steve and TechNet - I have had a several folks ask me to provide a 
further explanation the " "flux only" will have lower solder joint life 
than a BGA reflowed with solderpaste".  If you look at  many of the solder 
joint life prediction models, you will find that the solder joint height 
has a significant impact on overall solder joint integrity.  Take a look 
at IPC-D-279, Appendix A 3.1, you will find the Engelmaier-Wild model and 
the solder joint height influence is fairly easy to see. If an operator 
reflows a BGA using solder paste, you will get more solder volume and 
therefore a slightly increased solder joint height. With that being said, 
the BGA solder joint life will be better but maybe not necessarily 
required for a product use environment. As many of the TechNet responses 
have shown, it is common practice to use "flux only" reflow and meet the 
requirements of many IPC Class 2/IPC Class 3 use environments with no 
issues. Rockwell Collins has used "flux only' practices for many years and 
is just now transitioning to the new dip-able solderpastes for both 
increased solder joint reliability and ease of rework procedure. Rockwell 
Collins will be publishing a paper on the reliability of BGAs reworked 
with a dip-able solder paste process in the near future. The dip-able 
solder paste is not a new thing - many folks in the wafer bumping 
technology have been using it for years. 

Werner gives a much better explanation of the impact of solder joint 
height than my simple attempt. 

Hope this better explains my comments.

Dave



"Steve Kelly" <[log in to unmask]> 
06/03/2009 03:33 PM

To
<[log in to unmask]>
cc
"'TechNet E-Mail Forum'" <[log in to unmask]>
Subject
RE: [TN] BGA-113 package






Thanks everyone for the excellent feedback. Interesting information. 
Regards Steve Kelly
 
From: [log in to unmask] [mailto:[log in to unmask]] 
Sent: June-03-09 2:50 PM
To: Steve Kelly
Subject: Re: [TN] BGA-113 package
 

Hi Steve! Yes, you can reflow a BGA with "flux only" and not use 
solderpaste. Just remember that solder joint integrity is a function of 
the solder joint height. A BGA reflowed with "flux only" will have lower 
solder joint life than a BGA reflowed with solderpaste. And lower life 
doesn't not necessarily mean bad - just lower. The resulting BGA solder 
joints may be perfectly acceptable for the product use environment. Good 
Luck. 

Dave Hillman 
Rockwell Collins 
[log in to unmask] 


Steve Kelly <[log in to unmask]> 
Sent by: TechNet <[log in to unmask]> 
06/03/2009 11:10 AM 


Please respond to
TechNet E-Mail Forum <[log in to unmask]>; Please respond to
Steve Kelly <[log in to unmask]>



To
[log in to unmask] 
cc

Subject
[TN] BGA-113 package
 








Hi All,

We have a rigid flex that has a BGA-113 (microstar BGA) package to be
mounted to it. The routing in this area on the top layer leaves me with
.0005 of soldermask clearance from the edge of the BGA pad and .003 
distance
from the edge of the soldermask to the nearest track- in other words I 
have
.0035 of clearance from pad edge to next track assuming a perfect etch and
perfect soldermask registration.

Having rooted around Texas Instruments web site I believe that it may be
possible to reflow this BGA without adding solder paste to the pad - just
letting the ball collapse do the attachment. If my scenario is correct I
could open up the soldermask and not have too many concerns about bridging
between the BGA pads and the tracks. Any thoughts or comments would be
appreciated.

Thanks Steve Kelly 



Steve Kelly (PLEASE NOTE NEW E-MAIL ADDRESS)

(416) 750-8433 (work)

(416) 750-0016 (fax)

(416) 577-8433 (cell)




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