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July 2008

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From:
Grunde Gjertsen <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, [log in to unmask]
Date:
Tue, 1 Jul 2008 08:11:20 +0200
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Hi

IPC does not allow for a 20% reduction of the copper features, 13mm or 10% 
of a track can deviate up to 20% for class 2 and 3.
I don't think this is well formulated as it doesen't really allow for 
manufacturing tolerances, I believe most manufacturers interpret this in a 
more liberal manner and considers 20% as the manufacturing tolerance.
However, to let the 20% be valid for the larger copper features is a bit 
thick in my opinion. I interpret the maximum allowed reduction on pads as 
the absolute reduction on conductors. Meaning that if the board has 0,1mm 
tracks the maximum allowable reduction on pads is 0,02mm.

Best regards
Grunde




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Ryan Grant <[log in to unmask]> 
Sent by: TechNet <[log in to unmask]>
30.06.2008 21:43
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Subject
Re: [TN] IPC-6012A - allowable conductor width reduction interpretation?






Hi Joe,

I interpret it the same and end up specifying specific BGA pad size
tolerances instead of using 6012. 

By the way, per IPC, the conductor width should be measured from the
bottom of the pad, i.e. the interface between the copper and dielectric.
There is typically a 25um difference in width between top surface and
bottom surface, so measurements of pad width that only measure the top
surface might seem smaller than allowed.

Thanks,
Ryan

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Joe Macko
Sent: Monday, June 30, 2008 10:45 AM
To: [log in to unmask]
Subject: [TN] IPC-6012A - allowable conductor width reduction
interpretation?

All,

 

IPC-6012A with amendment 1, section 3.5.1, Conductor Width and Thickness
states, "When not specified on the master drawing the minimum conductor
width shall be  80% of the conductor pattern supplied in the procurement
documentation".  The PCB suppliers interpret this to mean that BGA pads
for example can be 80% of the pad diameter specified in the procurement
documentation, which is the GERBER files unless specified otherwise and
still be acceptable per IPC-6012.

 

I am interested to hear how other users handle allowable reductions in
BGA pad size from that specified in the procurement documentation.
thanks

 

Best Regards,

-joe

 


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