Re: gEDA-user: SMT assembly and gerbv lilbro.mosquito.net.nz

[John Griessen <john@xxxxxxxxxxxxxx>]

Here is a Q&A betweeen me and lilbro, a low volume assembly business
that wants to make geda circuit boards.  These are the questions I asked in regards to a batch of 50 boards.

=====================
[JG]Question 1. "Some software packages will output a file we can use to
place your parts."

[JG]If I give you a X-Y list of centroids generated by pcb, of the gEDA
project, I imagine all the symmetric shapes
will be usable, by a calculated averaged centroid.  Where should the X-Y
reference point
  be on a SOT23 transistor package?  The center of the rectangular plastic
body?

     [LB] Yes.....the centroid would end up being centered on the body. Most
software generates centroid data from
     the library, not from the gerber. It is not calculated, it is based on
the 0,0 location of how the part
     is drawn. That is why we (the company) will be faced with teaching the
machine manually until we can afford
     automatic gerber to centroid conversion software. It is a little
pricey.(about $8500.00)

  ========================

[JG] Question 2. 99% of my parts are going to be cut tape, or reels, but I'd
like to be able to use
  trays for parts that are left over from prototyping.

      [LB]I'm not sure where to get trays cheaply (actually haven't
researched it).

         [JG]OK. Not really a problem.  I have zero waffle trays, and they
seem expensive.  Next.

=========================

[JG] For handling parts on tape, if the job needs an amount, should I cut
the whole
  700 of one kind of resistor as one curl of tape?

     [LB] Yes.... it is much better to keep the tape as one piece. We will
reduce it down if needed.

=========================

[JG]At what length of cut tape is it better to send you the reel?

      [LB]That depends on how often you are going to have items assembled
using those parts. It gets expensive
      shipping back and forth. We will store reels for customers who have
jobs assembled often. They will only
      be used for the customer who sent them. That is the determining factor
for us. We really do not want to
      store for people who order once a year. We leave the cut-tape/reel
decision with the customer.
      We figure, if you have 1200 parts to put on boards, you will send the
reel.
      Also depends on how big the parts are. 0201's are pretty small.....and
a reel could hold 10,000 of them.

=========================

[JG]How can I mark cut tape so it doesn't slow you down?
adhesive label on the back side of one end of tape would be easy.

     [LB]An adhesive label will be fine, as long as the tape has it's top
peel away cover.

         [JG] So a label doesn't gum up the works, should it be on the end of
the tape and on the back,
         or on the peel away cover?

             [LB]A label attached to the peel away cover would be the best.
This is based on the idea, the tape will be emply when the job is complete.

[JG] Would a strip of paper stapled around a roll of cut tape be good for a
part label?
[JG]You could just tear it off before engaging the tape in a feeder...

     [LB]Yes this would be fine as well. You will find we are quite flexible
about most things.

=========================

[JG]Question 3. Should fiducials be two corners of copper intersecting?

     [LB]The best fiducials are round 1.5 mm circles. They require 3 mm total
clear space (for the whole fiducial).
      [LB]We can aim on anything that is not trapezoidal.

  ==========================

[JG] Question 4. I have a board to do that is 2.5 X 5.8 inches with 295 SMT
pads.
  It can be defined as a panel of 5 boards
that is 5.8 X 12.5 inches with 1475 pads.  Is that the best way to define
it?

     [LB] let me make sure I understand the question.  The design is one
board with 295 pads.
     You are planning to send it panelized in 10 panels (arrays) which have 5
boards per panel (array).

     [LB]Our price is based on single boards.  If I have the description
correct the price breaks down to:
      $25.00 setup fee
      $7.38 per board.
     $354.38 total (panelized) if no stencil is chosen for an option. I would
figure this is your target at the moment.
     $393.75 total if you sent all those boards single(non-panelized). (we
would have to put each board in the pick & place to assemble it)
     If you want us to separate the boards into individual boards, this is
does not cost extra.

     [LB]I think that will cover the questions....let me know if there is
something unclear.

James Long
Partner/Designer
Lil Brother LLC (SMT Assembly Division)

=======================


John Griessen
-- 
Ecosensory   Austin TX


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