Re: gEDA-user: any last minute advice prior to sending out for PCB fab

[Bob Paddock <graceindustries@xxxxxxxxx>]

On Wed, Feb 24, 2010 at 3:24 PM, Larry Doolittle
<ldoolitt@xxxxxxxxxxxxxxx> wrote:
> Hi -
>
> On Wed, Feb 24, 2010 at 02:40:50PM -0500, Bob Paddock wrote:
>> I'm making the assumption you will have a contractor build quantities someday,
>> in automated equipment.  These will (at least should) lower production costs:
>
> Although OT, I appreciate and try to learn from discussions like this.
>
>> Do you have at least three Fudicuals on all of your boards?
>
> I know what fiducials look like, but haven't seen a "footprint"
> for one within pcb.  Am I blind?  Is there a standard recipe for
> making one?

Simply a pad with no solder mask.  I use 30 or 40mil pads, with 50 to
80mil solder mask opening,
depending on how much space I have.

> The last time I asked a board loading house about fiducials, they
> said they gave up

Yes.  Because so few do it correctly.

>> Have you put Fudicuals on components, such as tiny QFN packages, or
>> even massive TQFP and BGAs.
>
> I don't think you said what you wanted to say.

Not sure.  I know our CM loves that I put fuducials on the QFN
accelerometer and compass IC's.
They get mounted at funny angles on the board.  My intent was  to say,
that if space is available put
fudcials at the component footprint level, when space is available,
especially on very small or very large packages,
that have multiple pins.  Putting on things like resistors and caps
would be silly.

I've learned most of this by working at a large CM, and 'The Hard Way'
of doing it wrong.

For example the job today is 5,000 boards.  When you get into
quantities, you start to do things
differently.  See the note at the bottom of my blog
http://blog.designer-iii.com/avr_isp_spi/20081116-10511-Digital-MEMS-Accelerometers-will-not-work-with-AVR-ISP-using-SPI
.

""You are supposed to isolated the AVR ISP pins with 1k resistors, as
the Atmel documentation shows".
This is true. However that takes four resistors per board, on a board
that already did not have enough space. Also at 50,000 units per year,
with an design lifetime of five years, that is 10,000,000 resistors.
After a while these resistors start to add up to real money, for what
is a single event at manufacturing time. Design for Manufacturing
always should be given consideration."


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