At 01:55 PM 2/27/2002 -0500, Mike Reagan wrote:
>[I wrote]
> > (2) The ability to truly flip a design or design section for re-use in a
> > new design which might predominantly be oriented bottom-up from the point
> > of view of the first design.
>I've read all the threads about wanting to view a board from the bottom up
>and I cant figure out why anyone would do this.

I think I explained it, but it was a bit densely stated. I'll dilate it a bit.

Suppose, I have designed a little piece of RF circuitry on the top of a 
PCB, including vias to layers just below, and this has been used 
successfully, tested, etc. Now I have another design where I would like to 
use this same circuitry, only I need to place it on the bottom. The rest of 
the design is on the top.

>     The IPC -D-325
>Documentation standard  states in        sec 4.2.6 VIEWING :   The layout of
>the board design should always viewed from the primary side of the board.

"Primary" side of the board gets a tad arbitrary with SMT designs with 
components on both sides. Sometimes there are even through-hole components 
on both sides.

Yes. But we are not talking about "documentation" of the "layout," but 
rather the layout itself, for one, where we might need to merge designs, 
flipping some of them and not others, plus, in documentation, we are 
talking about assembly drawings. Assembly drawings are traditionally done 
as viewed from the side being assembled.

>blah blah blah..     I have hit mechanical engineers and anyone else who
>wanted to view it otherwise on the head with a sledge hammer until the
>morons got it right.

Tsk, tsk. I'd be a moron too if I were being regularly hit over the head 
with a sledgehammer.

>     Why did I use a sledge hammer you ask? Because the
>only designs that ever came back with backward connectors  and parts were
>the freaking ones they wanted flipped.     Since they got my message that I
>wouldn't flip boards anymore, we have not had one design come back flipped.
>It was almost a regular occurrence because we had a mech engineer who
>couldn't grasps the concept of a primary side,     I have even seen BGAs,
>and earlier days PGAs flipped because someone thought it was a good idea to
>look at from the bottom.

I remember one layout where I was using a DIP relay and the only 
description I had of the relay was a catalog photo of it; the relay had a 
drawing pasted on top showing the pinout. Naturally, much to my chagrin, it 
was a bottom view. When I got the actual relay, there was even a tiny piece 
of text, not readable in the catalog, which said "pin view" or something 
like that.

Yes, I understand Mr. Reagan's concern. But I'd make an exception for 
*bottom assembly drawings," which are not used for fab but for assembly 
reference. One should be able to easily look at the drawing and at the 
physical board and say, yes, they put that diode in correctly. If that is 
easy for Mr. Reagan, my congratulations on his profound sense of spatial 
relations, with which I am fairly good, but not that good. And I think that 
most people are like me. I can read mirrored text without much difficulty, 
but determining orientations can get a tad dicey. I end up saying to myself 
"the cathode end will be near the IC" or something like that, so that I 
don't have to depend on "left" or "right." Which get reversed in a mirror 
view, unless it is rotated.

>     The advantage of the way the software flips it
>now is, you know it wrong when you look at it because the text becomes
>backward.    Yes  I said the view was wrong.    I really do not want this
>feature, I know some of you mechanical types do but I don't.   You can flip
>right now in the x axis or y axis, neither of which is an acceptable method
>of documenting a design.   The board must be viewed from the primary side
>looking thu the board.  (Actually ) I am going thru this same scenario right
>now with a chassis because some mech bozo doesn't know up from down.  Stick
>to the standards and everyone is on the same page

I don't think the standards conflict with what I am saying, but I could not 
find my copies at the moment....

In any case, bottom view assembly drawings are very common. Techserv does 
them, for example (or did,as I recall, last time I saw one of their 
assembly drawings).

How does Mr. Reagan propose doing a bottom assembly drawing where there are 
components on both sides? Especially if, as would be normal, there is only 
*one* assembly drawing for the board?

Abdulrahman Lomax
Easthampton, Massachusetts USA

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