PCB design / cheap manufacturers

[Emil]

Thank you very much for the advice, This will be very helpful for 
revising my design.

The PCB traces are 0.25mm, KiCad's default. I also thought they looked 
really thin but any thicker wouldn't be able to get between the pins. I 
hadn't thought about necking them. Originally I was planning for this to 
be a single-sided board to save money, but it turns out I would save a 
tiny amount of money going for double-sided, so I will take your advice 
and flood the top layer with ground.

I read about bypass/decoupling capacitors and wasn't sure if they were 
necessary so I left them out to save space, but since this is now a 
double-sided board I should be able to fit them on easily. I should also 
be able to terminate the unused pins.

pcbshopper seems to be very useful, thank you for pointing it out to me.

I will take your advice and create a second revision of my board.

On 03/08/16 21:02, Thomas Parry wrote:
> Hi Emil,
>
> A few comments:
>
>     1. You don't have any bypass/decoupling capacitors, this isn't great for
>     digital IC's - I would recommend adding some 100nF capacitors between each
>     ICs power and ground. Some larger (10uF) decoupling capacitors at the
>     raspberry pi connector to act as local energy resevoir won't hurt either.
>     http://www.allaboutcircuits.com/technical-articles/clean-power-for-every-ic-part-1-understanding-bypass-capacitors/
>     2. If you're going for a double sided PCB I would recommend flooding the
>     top layer with the ground net.  The solid reference plane reduces the
>     inductance in the current return path and prevents ground bounce.  This
>     will help ensure more reliable operation of your circuit.
>     http://www.elmac.co.uk/pdfs/Lord_of_the_board.pdf
>     3. Your traces look quite thin (it may just be the scale) I would ensure
>     these are with your PCB manufacturers capabilities.  Even if they are
>     within the manufacturers capabilities it is always good to make the traces
>     nice and thick (especially power traces) to reduce inductance and voltage
>     drop as well as making the manufacturing more reliable.  I see you're
>     tracking them in between pins of the IC but you could also have thicker
>     traces around most of the PCB and neck (temporarily reduce the trace
>     thickness) to pass between the pins.
>     4. It's good practise to terminate (to ground or power) unused inputs
>     (ideally through a resistor in case you change your mind later) to prevent
>     them toggling with noise.  The AY-3-8910 seems to have internal pull ups so
>     they're not a big deal but the 74HC245 has floating high impedance inputs
>     which could pick up noise.  This won't stop you're board working but I
>     thought I'd let you know.
>     5. In terms of PCB manufacturing it is worth having a look at
>     http://pcbshopper.com/. Enter your PCB details and get a comparison of
>     suppliers - basically a MoneySupermarket for PCBs. Most manufacturers will
>     be in China but generally they deliver good quality and you can pay for
>     faster delivery if you want.
>
>
> I hope that's useful and good luck with your build!
>
> Tom
>
> On Wed, Aug 3, 2016 at 6:55 PM, Emil <emil.carr at openmailbox.org> wrote:
>
>> It is single sided, yes, but I have the AY-3-8910 mounted on the bottom
>> side. It's weird, I know, but it works to save space.
>>
>>
>>
>> On 03/08/16 16:41, Gordonjcp wrote:
>>
>>> On Wed, Aug 03, 2016 at 03:38:52PM +0000, Emil wrote:
>>>
>>>> The new schematic / pcb design is at http://imgur.com/a/E9zL8
>>>>
>>>> Is it single-sided?  It looks like you've got one chip on top of the
>>> other, but I guess if it's on the bottom of the board it'll be okay.
>>>
>>> If you can do a single-sided version I can have a crack at etching one up
>>> for you.
>>>
>>>
>>
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