At 02:00 PM 12/11/98 -0800, Mark Koitmaa wrote:
>I have been asked by an engineer that I am working with to restrict the top
>side/bottom side placement of parts according to part values (all parts are
>0805's).  For example if I place a 10K resistor on the bottom side, all
>10K's should also go to the bottom side.  He does not want me to mix parts
>of the same value between two sides.
>
>He tells me this will significantly reduce assembly costs.  I have never
>heard of such a thing.  Is he correct?  I believe the extra layout time
>will negate any potential savings in assembly setup.  Any comments?

I'm sure he is right that it will reduce assembly costs. How much is
another question.

If it were only a matter of set-up costs, I doubt that these would
counterbalance the nuisance of making sure that parts of a value are only
on one side, and nuisance = design cost. Further, with some boards, this
requirement could impact noise performance.

But his requirement might also affect per-unit costs. I would think that it
might depend a bit on exactly what equipment is being used to do the
pick-and-place. This cost saving, though, would probably be small.

This could be one of those clever ideas which is penny wise and pound
foolish. Every day of delay getting a product to market might cost more
than is saved by shaving the last penny off of assembly costs.

But if this product is already on the market and this is a production
redesign, and the production quantities are really large, well, a million
pennies will buy a fair amount of design time.

And it is not terribly difficult to do what he is asking, unless the design
is really dense.

Now, if the design is not dense, we'll have to ask why it is not so, since
one could probably save *more* by making the PCB board smaller. That's not
just pennies.

[log in to unmask]
Abdulrahman Lomax
P.O. Box 690
El Verano, CA 95433

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