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Author Topic: FPGA ghetto mining / hunting for fpgas on ebay  (Read 6463 times)
sadpandatech
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November 08, 2011, 05:57:40 PM
 #21

keep in mind a roughly $20 per chip reballing and you're all set for a hunt.   Smiley

Can you refer me to a company that reballs BGAs for $20/ea?  I screwed up a few Spartan 6's during my early prototyping runs, and if it's really that cheap I'll have them reballed.

   E-tech responded to me rather quickly on a quote request.

  Few questions;
   1. Are the chips affixed to the PCB?
   2. Pb free or SnPb?
   3. How many do you need reballed?

If you're not excited by the idea of being an early adopter 'now', then you should come back in three or four years and either tell us "Told you it'd never work!" or join what should, by then, be a much more stable and easier-to-use system. - GA
It is being worked on by smart people. -DamienBlack
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rph
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November 10, 2011, 06:56:39 AM
 #22

do you have some instructions on how to build a reflow out of an oven?

Toaster ovens are not very good for BGA assembly - skillets/hotplates are much much more effective.
As you can monitor the process in real time with an IR thermometer.

-rph

Ultra-Low-Cost DIY FPGA Miner: https://bitcointalk.org/index.php?topic=44891
lame.duck
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March 25, 2012, 08:08:32 AM
 #23

...
Then solder wires directly onto the pad ...

I've try that. No can do... 1mm spacing is to small. I've used a chipset from damaged matherboard. And I'm rather experienced in soldering (11 years in work and other 10 as a hobbist).

http://zremcom.ru/images/stories/Stat/interes/2011/kulibin/rebol.jpg
dirtycat
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March 25, 2012, 09:08:41 AM
 #24

...
Then solder wires directly onto the pad ...

I've try that. No can do... 1mm spacing is to small. I've used a chipset from damaged matherboard. And I'm rather experienced in soldering (11 years in work and other 10 as a hobbist).

http://zremcom.ru/images/stories/Stat/interes/2011/kulibin/rebol.jpg

someone was bored lol

poop!
Dexter770221
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March 25, 2012, 09:52:51 AM
 #25

Extremly bored. But I can imagine that with very good soldering skills and tools it can be done. I've tried and I failed (maybe method was bad). Anyway I think that 2 layer PCB just with vias at 1mm spacing should make things much easier and give possibility to solder again BGA chip without reballing. Also, That PCB can serve as prototype board to new chips. Alot of soldering but changes can be made easily and quickly.

Under development Modular UPGRADEABLE Miner (MUM). Looking for investors.
Changing one PCB with screwdriver and you have brand new miner in hand... Plug&Play, scalable from one module to thousands.
Inspector 2211
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March 25, 2012, 10:22:36 AM
 #26

...
Then solder wires directly onto the pad ...

I've try that. No can do... 1mm spacing is to small. I've used a chipset from damaged matherboard. And I'm rather experienced in soldering (11 years in work and other 10 as a hobbist).

http://zremcom.ru/images/stories/Stat/interes/2011/kulibin/rebol.jpg

Such a "solution" is just a waste of time, as the inductance of the supply wires (core voltage, I/O voltage and GND) would be way too high and the FPGA would not operate reliably at any decent clock, if at all.

Consider a FPGA implementation of the Bitcoin mining algorithm (double SHA-256). There are 128 rounds of 256 bits each, i.e. 32768 flip-flops, all of which switch at the same time. All these flip-flops switching at the same time causes a momentary spike in power draw. Let´s say, for the sake of argument, from about 1 Amp when no flip-flops are switching to, say, a momentary power draw of 25 Amps (est.). If there is any inductance at all in the supply wires, the momentary power draw of 25 Amps will cause the internal core voltage to sag below the minimum acceptable core voltage, and the ground level that the FPGA sees to rise.

Below minimum core voltage, correct operation of the FPGA is no longer guaranteed, as the contents of flip-flops and even the contents of the configuration registers may be lost or corrupted.
ElectricMucus
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March 25, 2012, 06:17:44 PM
 #27

Even I know that there are decoupling capacities needed to avoid that. One could solder the capacities onto the power/gnd pins and the power lines onto them. The issue you described matter mostly for signals outside the chip which we practically don't have. The pins used to get the initial hashes in and results out would need minimal bandwidth.
Granted some clever i/o protocol would be needed but that wouldn't really be an issue.

Since the appearance of this photo I might even reconsider my idea.
The thing however is I yet have to find a offer where the thing would be really worth it.

First they ignore you, then they laugh at you, then they keep laughing, then they start choking on their laughter, and then they go and catch their breath. Then they start laughing even more.
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