Had you taken the time to run through the grits after sanding the chip, it is quite possible, neigh probable, the singles would not be having such bad throttling issues.
If you've done any recent research, most of the "mirror finish" stuff has been debunked, seriously.
link? every chip/heatsink i've ever owned has benefited from lapping. is a "mirror finish" necessary? no. Is it better to have an 800 grit finish than a 120? yes. (not saying it's a 120 grit finish before you micro-analyse. i don't have the chip on hand so i can't tell you what the finish is)
Other fpga manufacturers are not having throttling issues. Whether that is because they aren't utilizing the chips as well as you are, or because your thermal designs are terrible, is debatable. What isn't debatable is years of research in which techniques provide the best cooling for a chip, regardless of whether it's a cpu, gpu, fpga, or asic.
Umm.. they get plenty of "throttling", if they turn the speed up to insane levels. Technically it is just increased error rates, which indicates a need to reduce the speed to compensate.
what constitutes insane levels? I don't know of any other companies using that chip, so i can't say how aggressive their clocks are. I also mentioned its quite possible BFL has a highly optimized bitstream that's putting a lot of thermal pressure on the chip. What i'm saying is their thermal dissipation design is not adequate/optimized and it's causing issues.
thermal paste is designed to increase the surface area contact of chip/heatsink. you want to use the smallest amount possible because metal to metal is a better conductor than metal to tim to metal. logically, if nothing else, the smoother/flatter the surface, the less tim required, the better the cooling.
As i stated before, I do like your company and i do appreciate what you're trying to do. What I don't like is the excuses you are giving regarding blatant design flaws. It will be interesting to see what the final mini-rig product looks like and whether or not you've learned from mistakes you've made with the singles.
Perhaps you should have a go at the polishing experiment (or whatever else you can think up), and let us know how it works? I am always interested to know the results of real world tests. Before calling it a "mistake", prove that it is wrong.
a single-specific experiment? sure, send me one and i'll have a go at it
as far as experiments with lapping vs non lapped. google "does lapping increase performance" the general consensus is yes, if the chip isn't flat/has a rough surface, or the heatsink isn't flat/rough surface.
I'm not weighing in on the polished vs unpolished debate (or sanded properly or not) ... but I do want to point out this:
Other fpga manufacturers are not having throttling issues.
There are no other FPGA manufacturers that are utilizing these chips in this manner, so it's basically a first adopter problem for BFL in design and operation. Virtually all other FPGA applications do not utilize the chip to the capacity bitcoin mining does, which is, as I understand it, the fundamental problem BFL had in the beginning with their designs and simulations and the start/root cause of all the mystery to begin with.
again, i'm not debating that. If BFL's designers are so good (which again, it seems that they are) that they're running into thermal issues, they should create a solution that actually solves the issue. The box design is not
optimized for airflow, the heatsink is not
optimized for dissipation, and the sanding was not
optimized for heatsink contact, thus creating issues.
EDIT:
I'm not weighing in on the polished vs unpolished debate (or sanded properly or not) ... but I do want to point out this:
Other fpga manufacturers are not having throttling issues.
There are no other FPGA manufacturers that are utilizing these chips in this manner, so it's basically a first adopter problem for BFL in design and operation. Virtually all other FPGA applications do not utilize the chip to the capacity bitcoin mining does, which is, as I understand it, the fundamental problem BFL had in the beginning with their designs and simulations and the start/root cause of all the mystery to begin with.
Not only that, but BFL is the only one using a chip that has metal packaging, all the rest are plastic, so comparisons between them don't make a whole lot of sense..
metal packaging is a better conductor than plastic. not following there.