FEMTOVERB /Wavefrontsemi/ PCB layout

MetalGuy · February 21, 2006, 08:27:10 AM

Hi,

I found myself with a lot of free time these days so I decided to go digital and try to design a PCB for the Femtoverb project based on Wavefrontsemi's chips. Below is a preliminary version of the PCB layout. Please check it out and let me know if you have any remarks so I can fix it before posting the final version.

amz-fx · February 21, 2006, 09:01:13 AM

At first glance I do not think it will work unless you make it a double-sided board... right now, the surface mount chips look like they have to go on the bottom of the board which would put pin 1 in the wrong place.

regards, Jack

Mark Hammer · February 21, 2006, 09:02:05 AM

....but if you can iron that out...lordy mama...thanks!!

MetalGuy · February 21, 2006, 10:03:15 AM

Thank you for the input.

Quotethe surface mount chips look like they have to go on the bottom of the board

Yes, the AL chips will be soldered on the bottom /solder/ side. The view is from solder side anyway, that's why opamps' pin 1 seems to be on the wrong side.
Any other comments are welcome.
And I'm definately not going to iron this...

MR COFFEE · February 21, 2006, 11:34:12 PM

Looks like a nice project. Looking forward to hearing more!!

MetalGuy · February 22, 2006, 06:33:44 AM

Couple of fixes and mods were suggested by a well known forum member/moderator. I'll post the final version after everything is settled.

bassmeister · February 22, 2006, 07:18:52 AM

It's difficult to say from the picture, but the pads on the SMD devices seem like they are too short. If they don't extend a bit more than where the pins on the SMD package end, looking from above, you might get trouble when soldering. This is because you'd like to be able to heat both the pad and the pin simultaneously. The only place where you can put the tip of the soldering iron is on the pin itself if the pad is too small. The heat from the tip must then be conducted through the pin to the pad in order to heat it sufficently for the solder to adhere. Maybe not the correct technical english terms, but do you get my point?

This shouldn't be the case if the footprint is from a library in your PCB design software. If you draw it yourself, this should be considered in order to make the soldering easier.

MetalGuy · February 22, 2006, 10:09:50 AM

The SMD footprint is from my software library. I checked the data sheets for dimensions and I took some mesurements with mm ruler. It looks like there's enough space for soldering but I edited the library package and extended the pads a little bit more. You can print the picture at 300dpi to get it down to real size. There's still some space for extension if necessary.

Mark Hammer · February 22, 2006, 10:18:35 AM

I scaled and printed out the original last night and placed hips over top of it. Spacing looks fine.

If you have an acompanying traces-only image, that'd be nice to have. Otherwise, I spent some time digitally faking one last night that I'd be happy to post. Your call.

MetalGuy · February 22, 2006, 10:51:15 AM

I have traces only picture and I'm not posting it because I wanted with the help of those of you who are more into these things to agree on a layout. If you don't have any other remarks/considerations I will post the layout /traces only/ in the next couple of hours.
I just noticed that for some reason the newer fixed layout doesn't seem to show up and both pictures are in fact the same picture.
I hope everything is OK with this one:

Peter Snowberg · February 22, 2006, 12:52:38 PM

That looks GREAT!

I'm always impressed by layouts like this because I just default to two layers.

One tiny nit-pick and I do stress tiny, would be to move those extra pads between the ADC input coupling cap + leads and the shunt cap, to the traces that connect the - side of the coupling caps and resistors. I suppose there isn'y any reason why they wouldn't work 99.99% as well where you have them though. Count this change as sprinkled candies on top of the icing on the cake.

Again, FANTASTIC job!

MetalGuy · February 22, 2006, 04:49:56 PM

OK, below is the final version /for now.../ of my Femtoverb layout. There are still couple of more things that can be done but it's enough for a start.
The PCB is mirrored and ready to go now. The AL chips are soldered directly to the traces/pads /bottom/. To go down to real size print at 500dpi.
Thanks for all your input and help. Peter thank you for the good words, the encouragement and all your suggestions !
If you feel like something can be improved or moved around just let me know.

Peter Snowberg · February 22, 2006, 05:31:15 PM

Whoops... I see one more thing....

You didn't sign your artwork.

Now how difficult is it to etch this board with PnP? If it's pretty easy (I don't see why it shouldn't be), this will probably be the first DSP project that a LOT of people build.

Anyone building this, please post a build report.

MetalGuy · February 22, 2006, 06:05:42 PM

I'm not ironing this and that's for sure. At least not this time. A friend of mine will make it for me at work.
As for signing its well documented where it came from...
I don't know what's going on at Wavefrontsemi but more than a week ago I asked them how to order 2 pcs from each chip and all I got so far is only one email asking me whether I'm a company.
Peter, any ideas?

Peter Snowberg · February 22, 2006, 06:14:52 PM

Try posting on the Wavefront Semi forum and you should get a sales person fairly quickly. I know I've seen them post contact info there in the past.

I hope Small Bear will consider carrying these chips.

bassmeister · February 23, 2006, 09:18:15 AM

Quote from: Mark Hammer
I scaled and printed out the original last night and placed hips over top of it. Spacing looks fine.

So it's settled then.

Mark Hammer · February 23, 2006, 12:32:09 PM

Quote from: bassmeister on February 23, 2006, 09:18:15 AM
Quote from: Mark Hammer
I scaled and printed out the original last night and placed hips over top of it. Spacing looks fine.

So it's settled then.

Jeez I hate those small fonts where you think you see all of the word but you really don't.

I'm gonna print me up a PnP sheet tonight with the mask (6 copies, actually) and see how it goes. I had done some initial exploration preparing an SMD-to-DIP adaptor, and that seemed to work out nicely, so I suspect this will work out just as well.

MetalGuy · February 23, 2006, 02:20:11 PM

Impatiently awaiting the first build report!

Mark Hammer · February 23, 2006, 04:09:49 PM

Impatiently waiting to build! (I got my chips about a year and a half ago!)

Mark Hammer · February 27, 2006, 12:37:33 PM

Well, the board etched beautifully with PnP. It's fluxed and tinned, and awaiting drilling.

The thing with a composite (SMD plus through-hole) board like this is that one doesn't want to risk the chips suffering static damage by installing them first and then lumbering about with passive components. At the same time, even with great end-nippers it gets hard to get in there with the iron tip and reflow the solder on the pads quickly and efficiently after you've installed all the passive stuff.

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FEMTOVERB /Wavefrontsemi/ PCB layout