Minimig PCB run - interest thread

[Mikkel]

I'm interested in two to four unpopulated boards.

It would also be nice if you could sell components, as the parts are much cheaper if bought in bulk.

Having headers on the board instead of the connectors is a good idea, but I don't like the idea of the mini-ITX form factor. Headers would not take up much more space than the original connectors, probably even less, so it should still be possible to make it 12x12. 17x17 is just over twice as large, or twice as large as it needs to be in other words. Also, I suspect the boards might get much more expensive if they were made for the mini-ITX form factor, seeing as how you usually pay for the area when you order circuit boards. Having it fit in cabinets made for mini-ITX would be practical, but think of the drawbacks, much more expensive boards, and harder to mount them in smaller cases. At 12x12 they could probably still be mounted in mini-ITX cases without too much trouble, and they will also fit in nano-ITX cases.

Anders M.

[Mikkel]

Just checked out some PCB pages to see the cost of manufacturing the board.

I don't know too many details about the minimig board (didn't bother to count SMD pads, for example), so I used some numbers that seemed reasonable. I just wanted to get a rough quote anyways.

I checked with http://www.4pcb.com

I specified a 5'' by 5'' board, double sided, 0.062'' FR4, 2 layers, lead free, 1oz copper, 0.008'' min trace width, min. 0.02'' holes, 500 SMD pads on top, 0 on the bottom, 0.01'' SMD pitch, green solder mask on both sides and silkscreen on the top.

Qty    Same-day    1-day    2-day    3-day    4-day    1-week    2-week    4-week
50    $49.10    $39.32    $22.21    $18.29    $16.83    $15.85    $13.89    $9.98
150    $33.43    $26.76    $15.08    $12.41    $11.41    $10.74    $9.41    $6.74
250    $30.30    $24.24    $13.66    $11.23    $10.33    $9.72    $8.51    $6.09

The NRE is $149.

Surprisingly cheap!

I was going to check with Gold Phoenix too, but their page is down ATM.


Anders M.

[Mikkel]

The olimex boards wouldn't be good for this, as it wouldn't be possible to get more than 4 minimigs on the biggest board (2 if the 12x12cm form factor is chosen, as the width of the olimex board is 20cm), and it costs 132$.

This is 33$ (or 66$) per board, as opposed to as low as 6$ per board from 4pcb. The NRE of 150$ is negligible when several hundred boards are ordered.

It's a very good offer for prototypes and single projects, but for something like this, when hundreds of boards are needed, the bigger board houses have the best prices to offer.


Anders M.

[Mikkel]

The problem with the "bigger FPGA" idea is that the 208-pin package is the biggest one with pins from Xilinx IIRC. If you want to go higher, you need to go BGA. And BGA soldering equipment is expensive, you need at least a four layer board, inspection of the soldering requires even more expensive equipment, and for cheaper BGA soldering machines (that still cost several thousand dollars), the failure rate is high.

It would, in other words, get much more expensive.

It's an idea for the future, for those who want to experiment, but for the majority, who just want a very compact and practical OCS A500 to play with, staying with the 208 pin FPGA is the best solution

[Mikkel]

I believe there was some talk about using a 1Mx16 RAM earlier in this thread, as that would be much cheaper.

[Mikkel]

I don't think there are any good reasons why an XC3S500E wouldn't work, the board layout would just have to be changed a bit. It has more available I/O, more capacity and it's cheaper.

Personally, I don't think we should change too much of the original design before the first board run is ordered (or else, it'll never be finished), but changing the FPGA is no bad idea at all. In addition to the things already mentioned, it's newer too(AFAIK), and therefore less likely to get obsoleted soon.

Having to redesign the board and testing the new design could mean that we would have to wait a bit longer for the final board, but getting a board with a higher capacity FPGA and more I/O at a lower price is attractive.

PSRAM seems perfect for this, the only problem is, it's only available in BGA. At least it was the last time I checked. Too bad, as it's damn cheap and available in relatively large sizes. Some sort of dynamic RAM would probably be a good idea for the future, provided we could find a solution that didn't tie up too many FPGA pins, but implementing something like this in the core before the first board run would take a lot of time, so I think we should stick with one 1Mx16 SRAM chip for now.


Anders M.

[Mikkel]

Basman, make that 11$ for the RAM: http://www.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=428-1860-ND

[Mikkel]

About the SRAM: No, it isn't 22$ totally, no we don't need to look for expensive, obsolete RAM chips of the same type that Dennis originally used. The chips I linked to earlier are 1Mx16, so we only need one. This will also simplify the board layout. This should not be any problematic, as this chip was originally suggested by Dennis a bit earlier in this thread.