[SI-LIST] Re: Layout service recommendations
- From: "Moran, Brian P" <brian.p.moran@xxxxxxxxx>
- To: "'martin@xxxxxxxxxxxxxx'" <martin@xxxxxxxxxxxxxx>,si-list@xxxxxxxxxxxxx
- Date: Thu, 1 Aug 2002 11:40:16 -0700
Martin,
I've had a fair amount of experience with layout service bureaus and know
enough to know that the list of those doing it right changes with
regularity. So any bureau is only as good as their last design. I've been
out of the game for a few years so I won't try to give specific advice. I
remember Lee Ritchey's Shared Resources as a fine example of a good shop
back in the mid 80's and I've watched many others come and go. Many PCB
shops now offer CAD services as well. What has not changed is a couple of
basic tenants.
1) Document your design rules, including stackups, hole/pad geometries, and
trace width spacing geometries, and of course the actual net routing rules
by class. Even if they end up consulting and helping define stackup and
geometries, still document it. You can also help optimize routing density
by looking closely at hole/pad sizes and trace/spacing geometries, based on
package types and via grid spacing. Doing a good job of geometries is half
the battle in my opinion and service bureaus can be one size fits all. You
know where your cost point is and what geometry plateau you want to target.
Sit down with them and optimize. As far as routing rules, I generally used
the technique of tagging nets in the net list with net class codes and
providing a constraint file or table for each class code. You will likely
need to define several classes of nets. For optimal density with full
compliance you might have a dozen or even several dozen classes on a large
board. At the least break down your design by interface and by signal group
and provide clear rules for each. Make sure to set detour limits on critical
paths.
2) If the service bureau is not associated with your PCB fab shop or
assembly shop, make sure the service bureau is using approved DFM rules and
approved pad geometries and such. At least get the parties in touch with
each other to make sure your fab and assembly shop is ok with the service
bureau. You can really make life difficult for fab and assembly if your not
careful.
2) Define several check points in the route process where you can review the
incremental work. With a new vendor you might have more check points than
otherwise. Its a chance to catch and correct mis-steps or miscommunication
before you commit to the next stage. Most good shops have a documented
process flow with check points. You want to check the package after
placement and prior to start of routing. If your auto-routing or using
auto-constraints, you want to check the constraint files and routing
priorities prior to starting routing. Then depending on your design and the
routing methodology you may want to check intermediate results, however,
with a good rules based methodology this should not be required. Once
routing is done you sign-off prior to plotting. I don't actually like
checking other peoples work. If your inputs are clear no checking should be
required, but its nice to get a visual before commiting to copper.
4) Lastly and most important. I tend to shy away from shops that use hired
gun consultants for routing. While these guys are very good, they tend to
focus on throughput and often brush aside complex rules sets and avoid
interactive evaluation in order to get the job out. If you use them you
have to keep them honest. I prefer shops where people are salaried and have
a piece of the overall action, but are not doing piece work.
Brian P. Moran
Signal Integrity Engineer
Intel Corporation
brian.p.moran@xxxxxxxxx
-----Original Message-----
From: Martin Euredjian [mailto:martin@xxxxxxxxxxxxxx]
Sent: Wednesday, July 31, 2002 2:57 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Layout service recommendations
Being almost ready to go to layout I've been thinking about the issues of
sending a design out to a service bureau instead of doing it in-house.
Unless you work for a large corporation (I don't) you might not have access
to the $100K+ EDA tools and support infrastructure (budget, bodies,
equipment, etc.) you might need to produce good designs that work "out of
the box".
My particular design is a small 5x7 in board that has a 1.5Gb/s front end
which gets deserialized and fed into FPGA's etc. Most internal frequencies
are in the 100 to 200 MHz range, with wide busses.
Is it reasonable to assume that a good layout service can get this right the
first time? What should one look for? Are there any rules-of-thumb in
terms of cost? What guarantees should one demand? What should be the
hand-off process? What's the best way to assure success?
Much like the list of recommended PCB houses, it might be nice to assemble a
list of high-speed-capable layout service houses. I'll volunteer to compile
and post to this list.
Thank you,
===============================
Martin Euredjian
eCinema Systems, Inc.
voice: 661-305-9320
fax: 661-775-4876
martin@xxxxxxxxxxxxxx
www.ecinemasys.com
===============================
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