Nice board form. If you are looking at hole spacing for heatsinks, can I suggest you use the ones for a half brick DC/DC convertor? The spacing is 1.9" x 2.0", and because they're standardized they're easy to get anywhere so availability isn't a problem.
http://www.digikey.com/product-detail/en/VHS-95/102-1489-ND/1016697
They're also very cheap for what you get.

Quote from: ngzhang on November 08, 2013, 09:26:25 AM

By personal views, A3255 chip is cheap, if over clock too much will go with a huge increase of peripheral (DCDC, heat dissipation, etc)cost, then it's unworthy. just add a few chips and run under lower voltage. In other words, this is an art of balancing.

While I wish this were the case, it's not really true given the current price of BTC. At 12BTC/reel, it's US$8.40 per chip or $5.6/GH/s. Just for chips that's untenable, as you're at the same price per GH/s as the Bitfury chips which are more efficient and have a multitude of designs available already. I like the idea, but you need to revisit your pricing.

Quote from: Lucko on November 08, 2013, 07:31:55 AM

Yes but this is 10 chips because he has 10 chips... And 24W power usage. So yes only bit more then 50% at the moment but there is also efficiently that you need to think about. And overheating. I have a Chili board. And the biggest problem is power supply. It is on the limit and it needs additional cooling or the board slows down by 20%... So because you have save some $ on parts you need now additional cooling(fan and heatsinks) on power supply and that cost more then stronger power supply and uses more power since you need a fan and it runs in less effective part of operational range... Not to talk about lost hashes... So some parts are better if they are stronger...

I wouldn't say that, the power supply in the Chili actually runs fine with no airflow or heatsink at its nominal voltage and current (1V, ~90-100A) though it does get warm. The board just auto-overclocks in order to increase the hashrate, and the BFL can actually pull almost 20A each if they are really pushed. The RevB chips are actually even more power hungry than the first gen ones, which exacerbates the problem. The board doesn't slow down by 20% without extra cooling on the power supply, it just can't be overclocked as far.