Negative side-effects of using very thin PCB? - diyAudio
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Old 7th May 2014, 02:07 AM   #1
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Default Negative side-effects of using very thin PCB?

Hi Diy'ers,

I'm considering using a very thin PCB (~0.3 mm) for a DAC layout but wonder if - besides being potentially less mechanically stable - there might be other negative side-effects to using a very thin PCB?

One possibly negative side-effect could be the increased capacitance but at higher frequencies (25 - 100 MHz) track & component inductances seem to be more important in order to allow for effective decoupling etc. (according to e.g. Howard Johnson). Also, a thin PCB would allow for quite efficient cross-talk reduction between tracks.

However, I wonder if there could be some kind of negative side-effects to using a thin PCB - other than those mentioned above - that I don't know about ...

Might one/some of you know about/have experience with this?

Cheers

Jesper
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Old 7th May 2014, 02:09 AM   #2
DUG is offline DUG  Canada
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Board flex with surface mount parts...I would really avoid that.

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Old 7th May 2014, 04:49 AM   #3
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Hi DUG ... your reply made me realize that I could have been clearer in my wording when asking my question: I will be using multiple layer PCBs so even if a single layer may have some mechanical "flexibility" the combined layers would be reasonable stable, although probably not as thick as a 1.6 mm board.

But please "side-track" on the mechanical aspects - I should be able to find a solution to that. I'm more after if there are some kind of ("obscure") electrical side-effects - other than those I've mentioned - to placing a signal layer and a ground layer as close together as 0.3 mm.

Best regards,

Jesper
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Old 7th May 2014, 04:54 AM   #4
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Multilayer boards routinely have inner layers closer together than 0.3mm for 6 or more layers anyway.
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Old 7th May 2014, 11:58 AM   #5
marce is offline marce  United Kingdom
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I do boards with 2-16 layers in 1.6mm....
Use Saturn PCB toolkit and all the values for trace capacitance. inductance etc can be worked out....But never really known any issues for normal designs.
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Old 8th May 2014, 04:42 AM   #6
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@abraxalito & marce: Thank you both for your feedback.

I'm not familiar with what you do abraxalito but know that marce works with high-speed circuitries so if it works in this context it should be fine for my purposes.

Cheers,

Jesper
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Old 8th May 2014, 05:14 AM   #7
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Old 8th May 2014, 11:16 AM   #8
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Yep, multilayers, they are much better.
Take care of return current paths for signals which go thru vias. In 2-layer, usually, we gave just one GND plane on both sides, so there is *almost* no issue with vias.

With multilayer layout, say you have GND and VCC as 2-3 layers and 1,4 are for signal - if you go from 1 to 4 with via, then you change the return plane from gnd to vcc - this is failure, unless you stitch GND and VCC with capacitors in close proximity to via.
Another drawback is lack of ability to access inner layers for debug things - to cut traces.
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Old 8th May 2014, 11:27 AM   #9
marce is offline marce  United Kingdom
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Only a problem with very high speed in real life, and if you are doing high speed then you will have more than 4 layers, so can sort the layers out better. For most DIY stuff (and commercial) it is not an issue so I would not worry about it.
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Old 8th May 2014, 05:24 PM   #10
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The trouble is, it is already high-speed. LVC gates anyone? The speed is not a clocking rate, but rise/fall times And they are creeping into sub-1ns region.

Add a low-noise DAC and analog line-level circuitry with huge loop areas and hi-z all over the place, in the same enclosure...

EMC is must.
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