Re: Emulator boards

[Marc Randolph <mrand@pobox.com>]

On Tue, Feb 15, 2000 at 01:43:57PM -0500, David Cooley wrote:
> After the family crisis and the system crash I bailed out in SC, they sent 
> me to Ft. Bragg to do an installation at Womack Army Hospital. Kept us 
> there until the acceptance testing was out of the way and I got back 
> Saturday night. Went thru the boards last night and noticed they all seem 
> to have areas where the data/address lines are either missing copper or are 
> covered solid in one or two places. Verified my drawings had .010 spacing 
> and .010 minimum line width, PCB house spec'd at .008 minimum spacing and 
> .008 line width. Spoke with them about 30 minutes ago and they stated they 
> were having problems with some of their processing equipment... they said 
> if I would have been willing to pay the $200.00 "UL testing fee" it would 
> have caught the errors. Regardless, this is the 2nd time I've been hosed 
> and they agreed to refund the cost. Everyone that has sent me a check 
> please send me a note with an address so I can get the money returned.
> For a 100.00 item, this has been a ridiculous battle.

Wow.  I'm sorry you had to go through this, David.
I'm going to reply to the list in case someone else thinks
about doing this kind of thing in the future.

I'm an electrical engineer and we regularly specify we want our boards 
electrically tested, which is probably the same thing as their 
"UL testing" fee.  If we do not have our boards electrically tested, 
any board we get back might or might not have shorts or opens 
anywhere on the board (most always on the traces).  On a board with
12 layers and over 5000 traces, you can imagine how difficult it
would be to find any these opens or shorts.

Basicly what happens is that the board shops are like chip
vendors - they have an approximate % yield for a given technology
(line width and spacing).  In general, the bigger the width and 
spacing, the higher the yield.

If you specify electrical testing, you are placing the burden on them.
Estimating their yield, they will over produce by a few boards to make 
sure the run yields enough "good" boards that they can, for sure, 
sell you the number of boards you want.  They charge extra for this
because they must make or configure a custom fixture for your board
(some shops make a custom fixture, others use a universal fixture
that can be customized) to test each and every trace on the board.

If you don't specify electrical testing, you are basicly saying you
want them to build ten PCB's and you are agreeing to buy all ten, 
regardless of opens or shorts.  They charge less because they don't
have to over produce and don't have to dink with a test fixture.  
I know it doesn't sound right, but that's the way they typically
do business.

Again, I'm sorry you had to go through it all.  I've been through
it and it isn't fun chasing missing traces.

   Marc

-- 
  Marc Randolph     -    mrand@pobox.com    -     PGP keyID: 0x4C95994D
     If you have any info on the mid-60's car called the Bill Thomas
       Cheetah, or know anyone that might, please contact me.
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