Re: gEDA-user: powermeter board, with less ground planes :-)

[Steve Meier <smeier@xxxxxxxxxxxxxxxxxxx>]

If having to switch between nozzles is a significant issue then there is
room for a new pick and place equipment company that builds a
multi-nozzle tool. In reality, I doubt that it has much of an effect on
cost.

I wonder how the throughput of the pick and place tool compares to the
throughput of the reflow oven? or wash or final inspection?

Steve Meier

On Fri, 2008-10-31 at 20:31 -0400, Bob Paddock wrote:
> On Friday 31 October 2008 03:43:20 pm Joerg wrote:
> 
> > Much better. If you want to be extra good provide another 0.1uF parallel
> > to the AVDD caps, close to pin 3. C13 in your channel.sch file. However,
> > 10uF cermamics in SMT are already quite good these days, and cheap. If
> > you can get C13 closer to pin 3 that would also help.
> 
> "A bypass-capacitor dialogue peels back the layers, Part 1"
> http://www.planetanalog.com/article/printableArticle.jhtml?articleID=207602816&printable=true
> 
> Interesting article that says it is better to use bypass caps in different 
> size packages due to ESL effects.
> 
> Part 2:
> http://www.planetanalog.com/article/printableArticle.jhtml?articleID=208402807&printable=true
> 
> ...
> "David: Follow the currents. There is always a loop for current, there are 
> always fringe currents inside the ground plane, and voltage drops associated 
> with those currents. The cuts prevent the currents from mingling so they 
> could no longer couple directly from Input A to Input B (or the reverse).
> 
> Tamara: So this was an example of a ground plane gone wrong. The ground plane 
> with cuts in it actually performed better.
> 
> David: Yeah, most people believe that providing a low-impedance connection to 
> ground (like a plane) is enough. Sometimes that is true, but it's too one 
> sided. If you need really high isolation, you need to follow and control the 
> currents around the entire loop. "
> ...
> 
> Part 3:
> http://www.planetanalog.com/article/printableArticle.jhtml?articleID=209600453&printable=true
> 
> Do a search for "Bypass" on Planet Analog for related articles.
> 
> Doesn't look like they used PCB in the screen shots. ;-)
> 
> > Might want to rotate C11 and squeeze it in between R18/C12 so it's
> > closer to pin 4.
> 
> When "Squeezing" parts between things, consider what happens at the assembly 
> stage.  For example you put a tiny 0402 0.1 cap between to comparatively 
> large parts like a 1206 resistor and a large tantalum capacitor.
> 
> This could create a problem with the Pick&Place machine where your board
> might need two passes on the machine, increasing your assembly charges.
> 
> The 0402 cap will need a tiny nozzle to place it and fit between the larger 
> parts, while the larger parts need larger nozzle due to the part mass.
> If the 0402 part is on the outside of the larger parts then it is possible
> that the larger nozzle could be used for all operations in that area,
> this saves time hence cost.
> 
> 



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