and you need tell if you:
>plan for through hole mounting or SMT
>fully automatic mounting or much manual mounting (pad size, and locations
>can depend on that)
>mixed tech, i.e. power, digital and RF on same board, or separated
>02 components? Higher demands on the whole process.
>superBGAs? Need very flat boards.
>EMC secured areas with "Faraday" boxes (RF shield)
>copper plugged or solder filled cooling throughs
>metal hardback
>high speed signals that demand nickelfree lines
>size of panel (some very big panels can't be handled in ordinary lines).
>integrated R,C,L
>copper and gold thickness (if you have a tight budget, gold thickness can
>make dollars extra)
>air cooled frame to mount PWB on
>stiffened design to withstand vibration
>"G11" type to withstand temperature and moisture
>reinforced pads for heavy components, like transformers and coils
>separate ground and signal layer, or one common
>LF or ordinary, sane and good old Pb/Sn machine soldering (max heat
>difference)
>US restrictions if you have to ship outside the US (certain hitech board
>material)
>second source
>and more
>and more
and.........most important of all: treat the CAD engineer as a lump of
gold! I've seen and heard so many CAD guys be treated as second class
people, while, in fact, their jobs decide success and money. A alert and
motivated CAD'er can save lots of dollars per board for you, by doing smart
constructions.
Inge
----- Original Message -----
From: "Frank Kimmey" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Thursday, September 28, 2006 5:03 PM
Subject: Re: [TN] Build Structure Communication
Phillip,
To quote the great one "it depends"
What are you trying to achieve?
What is critical to your design?
How bad do you want to keep cost down?
Once you have answered these questions and probably a few dozen more you
can start to develop a plan to document PCB construction.
We do as follows with reasoning included:
1. Copper weight is always stated as starting. This allows us to ensure
we have a minimum copper weight for our current requirements and are not
reliant on various supplier plating processes. Also any additional
plating helps to derate our current calculations. And we can plan our
designs to use standard copper weights and minimize cost and lead
issues.
2. Dielectric thickness needs to be determined according to usage. For a
pure digital design a minimum dielectric thickness is enough but for
controlled impedance we specify a fixed dielectric and thickness.
Presently there are about 20 different standard stackups in my system
ranging from 2 to 10 layers.
We have designs that use .004 min dielectric layers with foil lamination
and designs that have set outer layer thickness that requires book build
processes, some are pure cheap FR-4 and others are RF Exotics, so we
need to have a large number of standard stackups. You may find you need
lots of standards or may get lucky and only have a couple.
Once you classify the design types you are producing you can then
develop the standard stackups you want your suppliers to use. Remember
to first talk to your suppliers and see if you can work concurrently to
find the best match and then to keep it as simple as possible to help
minimize your costs.
Hope it helps,
FNK
Frank N Kimmey CID+
Principal PCB Designer
PCB Programs
Powerwave Technologies Inc
Office 916-941-3159
Fax 916-941-3195
Mobile 916-670-0645
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Anslow, Phillip
Sent: Thursday, September 28, 2006 12:46 AM
To: [log in to unmask]
Subject: [TN] Build Structure Communication
Dear Fellow TechNetters,
Would you please share how you communicate your PCB build structures to
PCB fabricators, or, if you are a fabricator, how those which are
easiest to understand are presented to you.
For copper, is it best to quote (i) Nominal start weight or thickness,
(ii) minimum finished thickness to IPC-2221A tables before and/or after
plating if applicable?
For dielectric thickness, (i) specify value, (ii) give range (iii) leave
open?
Your advice and expertise is greatly appreciated.
Many thanks and regards,
Phil
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