I've been thinking about creating a couple shield boards that I will release as open source hardware projects. I may try and sell the blank PCB or completed boards I've not decided on the future of the projects.
I've noticed that some of the shield boards and open source hardware projects that exist in the world use through-hole components. As an example some of the projects from Evil Mad Scientist. http://www.evilmadscientist.com/ and of course the Arduino Duemilanove.
I'm assuming this is so that the end user can build or repair the board themselves. My professional experience has been to use as close to 100% of SMT components as possible for ease of manufacturing. Of course those projects usually were built in quantities of 200+ per run. For a smaller run project or a simple shield board I'm stating to think that through-hole may be a better choice.
That's frequently not possible. I had that very thought when building a DTMF decode shield, but as it turns out the wide SOIC is the same width package as the DIP, so it was impossible to do something sane like place an SMT footprint just inside a DIP footprint.
Then there's the fact that so many interesting ICs are SMT-only...
I like the idea of designing for both, but I can see the potential problem of finding ICs in only SMT packages. Also I've noticed some ICs are offered in both SMT and through-hole, but the T-H versions are much more expensive.
Well if you have to choose between the two types of components for your 'customers', I would say go with through-hole as everyone can handle those, while some cannot easily deal with SMD.
like place an SMT footprint just inside a DIP footprint
They don't need to overlap, although that would be ideal.
I know it is very hard, I spent almost a day unsuccessfully trying to design a board with only 2 ICs in both packages. A possible solution, albeit ugly, would be to place some of the SMDs on the other side (than the TH components) of the board. Well, if one really wants...
Here is my successful attempt to have both SMD and TH components on the same board:
Those components are the DS1307 and 24LC256, placed in the upper right corner of the board.
The SMDs overlap pins 2 and 3 of the DIP packages.
Obviously, the more ICs you want to apply this technique to, the more complicated it gets.
This is actually an Arduino clone I designed, now at version 1.2.
Some details can be found here:
florinc: Nice job on placing both SMT and T-H parts, I'm sure that took some work to make happen. You've inspired me to give the SMT and T-H combo board a try. I'll have to see how far I can take the idea, I'm not sure I'll be able to do all the parts but maybe most of them.
kg4wsv, thank you for pointing that out. Although DRC check reported no errors, indeed, a closer inspection reveals how "awfully close" the pads are.
I fixed the problem by modifying (in the library) the 2 DIP pads, making them round.
(Good thing I did not rush to send the board to manufacturing. Thanks again.)
Here is how it looks now.
Any other comments/suggestions would be hugely appreciated.
I'm currently working on a video-overlay shield board using the MAX7456 IC from Maxim. http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1246036323
It looks like there is enough space to make dual footprints (SMT & T-H) for all the parts. The only part that I can't find in both footprints is the MAX7456 IC which is only offered as an SMT part.
The three options I see:
Make the MAX7456 IC SMT only and the rest of the parts dual footprint. The downside of this option is someone hand building the board would have to solder one SMT part.
Make a dual footprints for all the parts, with the MAX7456 use a TSSOP-28 to DIP adapter with the MAX7456 soldered on for install onto the board. If someone hand building the board didn't want to solder SMT then there would need to be an SMT to DIP adapter with the MAX7456 pre-soldered onto the adapter, available for purchase.
Make an all SMT board
The first two options are making me think that an SMT only board might be a better choice for this project. My next board will probably make more sense with dual footprints.
