Hi Franklin,
You are correct, measurements should be from the widest point, where
ever that may be.
The 25um trace taper is a "rough estimation" based on my own empirical
data and varies slightly from supplier to supplier (15um to 30um) and
copper thickness. This is corroborated with the data from multiple
suppliers who bring it up whenever we get into arguments over
outer-layer copper feature dimensions... The taper seems to be there
regardless of pattern or panel plating, or cupric or ferric etch.
Thanks,
Ryan
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Franklin D Asbell
Sent: Monday, June 30, 2008 4:02 PM
To: [log in to unmask]
Subject: Re: [TN] IPC-6012A - allowable conductor width reduction
interpretation?
I am curious in your use of the term "per IPC". I do not believe that it
is
a 'shall' type requirement that width is always measured from the base,
there are some instances where the base will measure less than the top.
What IPC 6012 and IPC A 600 are attempting to convey is that you would
measure at the widest point of the conductor whether that be at the top
or
bottom of the conductor itself ( and I suppose in some strange
situations,
even the middle). If you have a copy of IPC A 600, look at image
IPC-600g-321i.
Finally, I am again curious where you got the figure of 25 um???
Franklin
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Ryan Grant
Sent: Monday, June 30, 2008 2:44 PM
To: [log in to unmask]
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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