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December 2011

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Subject:
From:
Rex Waygood <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Rex Waygood <[log in to unmask]>
Date:
Wed, 14 Dec 2011 16:37:40 +0000
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I'm not sure this will get you far.
All of the Gerbers are modified by the PCB manufacturer to allow their processes and materials to give you as near a representation of the original Gerbers as they can. If they want to change the 'output', ie what the pcb will look like, for any reason then they need to ask.
I think you could end up chasing your tail.
Regards
Rex


Rex Waygood
Technical Manager

Hansatech EMS provides value manufacturing through engineering and quality

Hansatech EMS Limited
Benson Road
Nuffield Industrial Estate
Poole
Dorset BH17 0RY
United Kingdom
Tel:
Fax:
DDI: 
01202 338200
+44 (0)1202 338202
01202 338222 
[log in to unmask]
www.HansatechEMS.com 


 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Phil Bavaro
Sent: 14 December 2011 15:48
To: [log in to unmask]
Subject: Re: [TN] BGA SMD vs NSMD

It is possible to have the gerber soldermask layer that the fabrication house used (after they modified yours) sent to you.  Then you can use a gerber comparision tool to look for differences.  I agree that you want to have the final and best representation of the gerber incorporated into your library.  

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of William Noel
Sent: Wednesday, December 14, 2011 3:44 AM
To: [log in to unmask]
Subject: [TN] BGA SMD vs NSMD

Hello all - I am looking for some advice on building our standardized CAD models for our BGA's.  I have been creating our CAD models using the IPC LP Calculator as a companion tool to the IPC-7351 SM Design and Land Pattern Standard. One of the conventions that 7351 recommends is creating solder mask shapes at a one to one size relative to the pad size.  To my understanding this creates a Solder Mask Defined (SMD) solder joint.  Additionally I believe this  solder joint is termed a "non-collapsing" solder joint using the IPC terminology.  When the solder mask is relieved by a slight amount (in other words if the opening in the solder mask is slightly bigger than the pad geometry) then this creates a Non-Solder Mask Defined (NSMD) solder joint which I believe is termed a "collapsing" solder joint using the IPC technology.  Our fabrication notes indicate that the solder mask may be "swelled" by the fabrication house as appropriate to create a high quality solder joint while simultaneously insulating routes that are in close proximity to the joint itself.  The concerns we have are that now the fabrication house has possibly modified our artwork and we have no way (without close examination under a microscope) of knowing if the soldermask opening was enlarged and if so by how much.  We don't really want to leave it up to our designers to modify the soldermask opening for the "standardized" CAD models coming out of library.  We would prefer to have our CAD model fully represent what is being built.  Any advice on this subject would be appreciated.  Thank you.

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