@aerobatic: how much does slicing, packaging and testing contribute to the production cost of Bitcoin ASICs?
And separately, how about the effect of yields on cost?
I would assume that AM has experience now in this field, after 2 generations of chips and battling with problems?!
bitcoin mining chips, with their large number of replicated cells (hash engines) are very good for yield - probably the best possible case that a foundry could wish for, as often they can still find useful and functional chips even if not all the hash engines are operational... whereas if you're making Apple A6 chips, even a single defect is fatal and the chip will be rejected. you need every single circuit to work and any single defect on the die spoils the entire die, wheres for bitcoin mining, they can cope with some, and perhaps even a lot of defects and still have a useful and valuable asic. for that reason, its not uncommon for bitcoin asics to have exceptional yield compared to regular asics, thus the yield factor doesnt become as important as the cost of each wafer and the efficiency of the overall design.
that said, as you know, wafers are round, and asics dies are rectangular.. thus the larger the die, the less number of dies fit onto a wafer.. because of wastage around the edges of the wafer where the circle intersects the many rectangles.. and if any part of th rectangular die touches the edge, the die is of course unusable. asicminer uses very small dies, which should mean they will get less wastage at the edges of the wager and should have more usable dies per wafer. on the other hand, the edges of each die where they're sliced puts a border around each die, which itself adds some wastage (die streets) and a larger area of the wafer is given over to edges versus usable die area on bigger dies.
i think asicminer uses small dies now because they have always done... whereas there would be less packaging cost, and lower board costs, jf they used larger dies with more hash engines per die. there's some ineffiencies in using small chips that are not fully optimum. in bitcoin asics... there are also various efficiencies of using small dies.. in that they might be able to be air cooled without individual heatsinks.. which saves cost and manufacturing time... however, having each tiny die have its own package could become more costly than having larger dies with fewer packages. personally, i think that larger dies are the way to go. i think having tiny dies, thus high numbers of packages and larger boards etc.. adds more points of failure, and more board power losses.. so I'm in favour of larger dies in general. not necessarily huge ones any longer (as they require exotic cooling, which we've all seen isn't as reliable).