I know from experience that if you need to rework the BGA on one side, the one that is mirrored will be affected and can go into partial or full reflow. You will need divine intervention to prevent collateral damage, especially if the CCA is coated. For that reason we do not allow mirror imaged BGA designs. We had all kinds of issues with these.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of David D. Hillman
Sent: Tuesday, December 11, 2012 5:35 PM
To: [log in to unmask]
Subject: Re: [TN] Data Concerning Solder Joint Integrity of Assemblies with "Mirrored BGA" Configuration

Hi Inge! The TechNetee's lead me to a couple of older but good papers showing that having "mirrored" BGA or CSP components has an influence on solder joint integrity. It is a topic I wanted to explore since many product are now encountering this configuration as assembly size is getting much smaller than 10 years ago.  Lots of factors in play but the interaction of component configuration and board warpage is one of the topics described in the published literature.

Dave



From:   Inge Hernefjord <[log in to unmask]>
To:     <[log in to unmask]>
Date:   12/11/2012 04:43 PM
Subject:        Re: [TN] Data Concerning Solder Joint Integrity of 
Assemblies with "Mirrored BGA" Configuration
Sent by:        TechNet <[log in to unmask]>



Dave, what do they base that apprehension on?
Inge

On 21 November 2012 23:27, David D. Hillman
<[log in to unmask]>wrote:

> Hi gang! I have been looking for some data and am not having any great 
> success so I thought I would ask TechNet! I am looking for solder 
> joint integrity data for BGAs and CSPs where you have a two sided 
> board and
the
> BGAs or CSPs are "mirrored" (aka side one has a BGA exactly opposite 
> of
a
> BGA on side 2).  I have found publications discussing the impact of 
> mirrored BGAs due to rework but I am looking more specifically for the 
> influence of having a mirrored configuration  (or even a partially 
> mirrored configuration) on the solder joint integrity in thermal cycle 
> conditions. There seems to be some industry tribal knowledge that 
> having
a
> mirrored BGA/CSP configuration causes a degradation in solder joint 
> integrity but I am not finding supporting data in the industry
literature.
> If you know of any published papers/reports, please send me the 
> citation and I can run down the papers.
>
> TIA
>
> Dave Hillman
> Rockwell Collins
> [log in to unmask]
>
>
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