I do not know if this is "permissible", nor do I know if it needs to be.
I think this design is a very good idea for mounting decoupling caps, perhaps even input signal or latch-up resistors and other components as well.
The only concern I see is the potential stress that the large dogbone pads will place on the caps during any temperature cycling while operating or in storage. The solder joints that are formed appear to be very rigid, with little modulus of elasticity.
You may wish to thermal cycle one or two scrap CCAs and check for any evidence of chip cracking as part of a qualification of the design.
I certainly don't anticipate any issues with current carrying capacity, and it appears you have plenty of electrical clearance, at least in the photos.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of [log in to unmask]
Sent: Tuesday, November 15, 2016 1:54 PM
To: [log in to unmask]
Subject: Re: [TN] SMT Ceramic Cap, pad skew/offset
Steve,
I thank you very much for posting my pics. I have experienced a lot is issues with TechNet forum server. That is why the multiple inquiries. Thanks a million. My main concern with this design is electrical spacing violation. Once given the go ahead to destroy the card will be measuring external copper pads distances. Is this practice permissible by IPC Standards.
Victor,
From: Steve Gregory [mailto:[log in to unmask]]
Sent: Tuesday, November 15, 2016 1:36 PM
To: Hernandez, Victor G <[log in to unmask]>
Cc: [log in to unmask]
Subject: Re: SMT Ceramic Cap, pad skew/offset
Hi Victor,
I have your pictures posted. Sorry I didn't post them earlier but there's been a few fires here at work. I only posted three of them because it looks like there were duplicates of the same sort of images. This all looks purely intentional to me. I have seen the same sort of layout recommendations for decoupling caps in a few vendor guidelines...
http://stevezeva.homestead.com/SMT_Cap_Pads-1b.JPG
http://stevezeva.homestead.com/SMT_Cap_Pads-1c.JPG
http://stevezeva.homestead.com/SMT_Cap_Pads-1e.JPG
Steve
Steve
On Tue, Nov 15, 2016 at 11:50 AM, <[log in to unmask]<mailto:[log in to unmask]>> wrote:
Steve,
Can you please post this pics to the forum for me, Thanks,
Back side of BGA. Ceramic capacitors skew from center of pad. Any Pro and Cons on this practice. Perhaps, spacing violation????? Analysis is pending/Ongoing......
Victor,
-----Original Message-----
From: Leadfree [mailto:[log in to unmask]<mailto:[log in to unmask]>] On Behalf Of Steve Gregory
Sent: Wednesday, February 03, 2010 11:57 AM
To: [log in to unmask]<mailto:[log in to unmask]>
Subject: Re: [LF] [TN] track lifting
Hi Werner,
I didn't know you wanted me to post the picture last night, so I got it up now. It's at:
http://stevezeva.homestead.com/files/Werner_Buckle.jpg
I'm working swing shift now...
Steve
-----Original Message-----
From: Leadfree [mailto:[log in to unmask]<mailto:[log in to unmask]>] On Behalf Of Werner Engelmaier
Sent: Wednesday, February 03, 2010 9:41 AM
To: [log in to unmask]<mailto:[log in to unmask]>
Subject: Re: [LF] [TN] track lifting
Hi Everybody,
I sent Steve another 'buckle-up' trace lifting picture to put on his site. So now, together with Brian's case we have 3 documented occurrences.
So, please, as I wrote to Brian:
I would appreciate pictures, possibly also to Steve, that I could use in my reliability column—this is a failure mode fairly new and unknown to most people.
If you could, I also would appreciate the base material, the peak reflow temperature, the cooling rate after reflow, the Cu trace thickness and whether it was covered with solder, and what solder. I now, its asking a lot, but only with all the pertinent info can we make sense of this.
Werner
-----Original Message-----
From: Stadem, Richard D. <[log in to unmask]<mailto:[log in to unmask]>>
To: TechNet E-Mail Forum <[log in to unmask]<mailto:[log in to unmask]>>; Werner Engelmaier <[log in to unmask]<mailto:[log in to unmask]>>
Sent: Wed, Feb 3, 2010 9:33 am
Subject: RE: [TN] track lifting
Like Steve, my first thoughts were that the BGA in the picture was apparently impacted, or somehow lifted and then put back down and reflowed.
However if that had happened, it could not have happened without many other traces on each side of the lifted ones also being lifted and damaged, but they are not.
Therefore I agree with Werner, that this is a case of damage due to severe CTE mismatch. I have never seen this before.
Burke, I'll take you up on that bet. I doubt that there will be any delamination issues. This appears to be a case where the PWB expanded and shrunk back in the X and Y axis during reflow or temperature cycling, but I doubt that it saw any significant Z-axis expansion.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]<mailto:[log in to unmask]>] On Behalf Of Werner Engelmaier
Sent: Wednesday, February 03, 2010 8:13 AM
To: [log in to unmask]<mailto:[log in to unmask]>
Subject: Re: [TN] track lifting
Hi Brian,
I would appreciate pictures, possibly also to Steve, that I could use in my reliability column—this is a failure mode fairly new and unknown to most people.
If you could, I also would appreciate the base material, the peak reflow temperature, the cooling rate after reflow, the Cu trace thickness and whether it was covered with solder, and what solder. I now, its asking a lot, but only with all the pertinent info can we make sense of this.
Werner
-----Original Message-----
From: Brian Chandler <[log in to unmask]<mailto:[log in to unmask]>>
To: [log in to unmask]<mailto:[log in to unmask]>
Sent: Wed, Feb 3, 2010 7:28 am
Subject: Re: [TN] track lifting
We just conducted a study on acceptable strain levels for lead free products.
Our BGA test coupons showed this exact result from excess strain.
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