ATMEL Mega1284P evaluation board avalible

Robert,

  • for example: here are 2 eagle files, you can open them and copy the battery holder part..

http://garden.seeedstudio.com/index.php?title=Wiseduino

http://www.wiseduino.com/?cat=3

  • the cr1220 battery holder on the board seems to be this type:

http://www.ebay.com.au/itm/10pcs-CR1220-1220-Computer-Battery-Socket-Holder-Case-/300553623491?pt=AU_B_I_Electrical_Test_Equipment&hash=item45fa6457c3

bat1220.jpg

So I've traded some e-mails with the company that made skyjumpers stencils for his board, which had some bridging issues after reflow on the FTDI chip.
The guy I'm talking to says 28 SSOP are the devil's work! 8)
He suggested he would adjust the stencil opening to be 2mil narrower in all directions - but suggested instead going to the 32 pin QFN package.
Does anyone have a line on part that uses 32 QFN with thermal pad on the bottom that I could edit into an FT232RL?

I know I could do it from scratch, but my eagle skills are slow in that area, took me several nights to come up with this FCI socket, doing the math calculations, intrepreting the mechanical data sheet.
(I can't even locate the library I created! Eagle has it tucked away somewhere - I can open it & see my part, I just can't see it on my harddrive anywhere!)

It looks like the "ftdichip" library that comes with EAGLE includes the QFN version...

I have been thinking about this and I think I would avoid QFN (quad flat no-lead). Without an x ray machine, there is no way to inspect the component after reflow, so there could be bridges you would never see. If there are bridges, the only way to fix them is to remove the entire chip. Since it has four sides, removing it, even with a hot air rework station, is going to be a challenge. And then, how do you get it back on without disturbing the neighboring components? You can not hand solder it, because there are, well, no leads. And, assembly houses charge more if your board has no lead components and/or fine pitch components (but FTDI chip is not fine pitch).

I have been told by many people that swelling the apertures works well to solve the bridge problem. The FTDI chip does have tight leads, but they are not technically small enough to be referred to as "fine pitch." Without swelling the apertures, I got bridges, but I was able to wick them up and all was fine. I doubt I could do that with QFN.

Just my 2 cents. On the other side, heck, I'm willing to give it a try! Maybe I'll be pleasantly surprised!

Dang! Look the bodies of the 2 chips.
I'm liking the 28SSOP more after seeing them together.
I think I'm with you, swelled aperture.

I just spent a couple of hours creating a footprint too, as I didn't have an option for QFN - but I see why, somehow I grabbed the FT232 from the "smartprj" instead of the "ftdichip" - probably because I started out by stripping down a duemilanove and building back up.
The two libraries use diferent looking symbols too for the 28ssop part/

That's amazing. And that stencil guy thought this would be an improvement? Well, to be fair, maybe there are QFN packages with bigger pins and spaceing.

First lot of 10 PCBs ordered, sans the small battery.
Stencil & parts ordering next ...

Yay!

Cool!

All parts ordered except the stencil. Waiting to get confirmation from itead's factory that it is producible, then will order the stencil. Hopefully assemble the first board(s) the weekendof July 9 with Skyjumper's help.

New Boards are in! "Bobuino" for lack of a name - never did come up with a name to put on the silkscreen!
Already have plans for this weekend, should be assembling next weekend.

Submitted order of 10 to itead June 28, received 12 today July 15

Wow very nicely done! With the risk of sounding needy could you keep track or photo the order in which you apply the parts to that board? I have read most of the thread as you have designed this and it is amazing how many parts you have managed to put on the board! My guess is that you would have to apply parts in a particular order otherwise you will have great difficulty.

I probably don't need the latest greatest board but, I would still like to have because, it sounds so cool!

Mark

"order in which you apply the parts to that board"
Well, being surface mount, I imagine all the surface mount parts will be applied first, then flowed in the oven, and the thru hole parts will be hand soldered in.
I would imagine start on one corner of the board and work across, or perhaps do all the caps, then all the resisters, then the LEDs, then remaining big parts.
The only part I think will be difficult will be getting a microSD on the back of the card after the top is reflowed. The pins on the backend are tiny, but clearly exposed, so maybe not that bad.
itead studios seems to have built a nice PCB for me, so it looks like I have a good base to apply the parts too. Now I just need better eyes for plopping those parts down :smiley:

Thanks for the reply.

"Now I just need better eyes for plopping those parts down smiley-grin"

I have yet to try soldering SMT parts and I dread the though of soldering them down. I do need to learn it at some point though. I have a cheap magnification visor I found at a hobby shop and I have access to a magnifier with a light at work. Looking at my new Mega I can already see that a magnifier is a MUST for me.

Mark

In the pre-SMD days you would normally load parts in order of their height, lowest through to highest. This way you could flip the board over to solder without them falling out.

That probably still applies to the PTH parts, with SMDs going on first.


Rob

We can try a few things. Yes we can try to hand solder the micro-SD socket. We might be able to reflow the mocro-SD socket first, then flip it over and reflow the rest, with suface tension holding the bottom part on. I don't think that will be feasible, though. Because reflowing the top measn using the stencil and squeegie to apply the paste and I doubt we can do that with the micro_SD part applied.

Maybe the trick will be to reflow the top, then use the hot air rework station to apply the bottom parts. As I think about it that might be best, although we'll need to be careful to apply just enough heat in just the area we need, so the parts on the other side stay put.

As for the order of parts, most recomendations I have read are to put the big ones on first followed by smaller ones. I have found with only a few exceptions, it does not make much difference. My board has a few spots where that is better though. I make a checklist, have an enalrged gerber next to me, use a few magnifiers and its off to the races! The checklist is key though.

I appreciate the tips and ideas on applying parts. I have been able to solder since my teens so, over 20 years but, I know that I still have many things to learn. Recently, I have been soldering a lot and I have been finding little things that I wish I would have known in the past. :astonished: Some of my past work looks very sloppy compared to now.

Mark

Thanks Skyjumper. Next weekend going to work for you?
Can you send me your checklist? I'll make one up for my board, and some expanded pictures also.

Just stumbled onto this and it looks very interesting. I was looking to start using the 1284p so if i could get it in an arduino compatible board that would be great. I will keep an eye on this thread and hope all the assembly goes well.

Thanks Subterranean, I am looking forward to attempt ass'y on Saturday.