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Date: | Mon, 16 Oct 95 15:22:26 EST |
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Hello All,
I have three design questions open for discussion or debate.
Please feel free to respond to any or all.
1.) Circuit Routing Programs:
I have seen several designs where traces are routed at the minimum
spacing, between two pads, when they could be routed differently to
optimize spacing. These are typically designs with multiple traces
running between pads. It appears the design algorithm will not
automatically jog a single or multiple lines to maximize the spacing.
Do effective, reliable, high quality programs exist that could
maximize these types of designs? Does the design community support
these programs, assuming they exist? You can guarantee I would notify
the customer and let them review any changes prior to making
implementing any changes.
2.) Plated Hole/Trace Spacing:
In an effort to increase density I have seen a few designs where non
functional pads have been removed from internal layers to rout the
traces closer to the holes. The problem is that the traces have been
0.20 mm (0.0080) from the hole barrel. Referring to Table 5-10, in
IPC-D-275 the minimum standard fabrication allowance is
0.25 mm (0.010). Therefore, using this value I would predict the
minimum finished spacing I could assure the customer would be 0.08mm,
(0.0030). I subtracted half of the minimum standard fabrication
allowance from the minimum distance found between the trace and the
hole barrel. Do you concur with this result?
3.) Drill/Gerber Data Misregistration:
It is more common to find customers who provide drill data and gerber
data which misregisters, approximately 1 out of every 5 jobs. We
typically see this when Gerber data is provided in 2.4 format and the
drill data is provided in 2.3 format. The amount of misregistration
has been 0.03 mm (0.0010). We have also been told this
misregistaration can be a result of the design software used. The main
concern is this misregistration can effectively reduce your hole
location allowance by 33%, considering 0.25 mm (.010) DTP. We correct
the errors but wonder if this trend will be improving.
Thanks is Advance for your thoughts,
Mark Santos
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