Why is Intel so secretive about Phi’s die?

Pictures can reveal more than you think

Intel phi logo 87x65 Why is Intel so secretive about Phis die?Ever noticed that Intel is deathly afraid to talk specifics about not-Larrabee Xeon Phi, especially die size? Ever wonder why there are absolutely no pictures of it floating on the net?

SemiAccurate did ask about die sizes, for pictures of unlidded parts, and all the stuff you would think Intel is proud of but forgot to include in the presentations. Luckily for us, the answer we got back is absolutely consistent, not the usual wishy-washy ballpark deflection we are used to. Unfortunately however, that answer was a consistent, “no”. There is a good reason why they are deathly afraid to release this too.

The closest we got to a picture was Thomas Ryan’s shot of a chip in the hand of an Intel spokesmodel. Those models may be chosen for their looks, but they are well trained too, there is nothing to get a size reference from in the picture. It is unquestionably huge, but how large is not discernible. Some people claim it is about 350mm^2 on the Intel 22nm FinFET process, a number that our moles say is laughably low. Unfortunately our moles shut up after they stop giggling.

Intel won’t show any bare boards either, the few shots that are out there have heat sinks or are older versions, quite likely not 22nm silicon either. They all have the PEG connectors off the back, the real boards have them on the top. This ‘minor’ detail is more than enough to question what the pictures are, and then you have to ask what chip is on them.

Luckily, SemiAccurate’s moles have got us a picture, it isn’t stunning quality, think more of what the author takes himself rather than correctly in focus. That said given the circumstances it is amazing he/she/it/they actually snapped it. Well done. With a little pixel counting, the exact die size is… we’ll get to that in a second. That is the least of the news though, there are a lot of interesting details that come from the picture, especially surrounding Haswell.

The first bit you probably care about is the die size. Unfortunately the bare board has a heat spreader on it that completely obstructs the die so we can’t give you any hard numbers. Worse yet the heat spreader is much much larger than the die could possibly be. Take a look at the shot below, blurry it may be, but we can’t find any other anywhere. Once again, thanks to our mole for it.

Phi shot WM Why is Intel so secretive about Phis die?

The bare board shot with Xeon Phi die

Based on pixel counting and comparisons to known size bits on the board, SemiAccurate’s crack team of competitive intelligence experts went to work. They were a bit grumpy that their day job of scraping gum off the sidewalk was rudely interrupted for lesser tasks, but we do pay badly so they counted pixels for weeks while the gum piled up. The results were between 46 and 48mm in length, 36 to 38mm in height for a rough estimate of between 1650-1800mm^2. Yes we did the numbers much closer than that, but given the blurriness 17 digits is rather silly to report. Did you learn nothing in high school science class?

Still a lowball number of 1650mm^2 is a tad higher than the equally farcical 350mm^2 number some are touting. SemiAccurate’s moles say the Knights Corner die is closer to 700mm^2 than 600, but this image sheds no light on that part either. Even a rough estimate of the silicon area is pointless given the disparity between the heat spreader area and Intel’s maximum reticle size. Why use such a massive heat spreader for a chip that isn’t half that area? Spreading heat may seem like the obvious answer but it is unlikely to be the reason. We won’t go into technical details about why, take a night class in thermal management if you really want to know.

Remember in Thomas Ryan’s story he mentioned GDDR5 being on an interposer under the lid? GDDR5 is on the board, but what about L3 or other cache? No one has talked about construction before of after Thomas’ scoop, nor has Intel confirmed or denied anything about it either. That said, we believe it is accurate.

So, any guesses the spreader a large die would need if you stuck it on an interposer and slapped some cache around it? Some cache that doesn’t show up on the spec sheet either, according to Intel all of that is on die and private to the respective core. So what could be there? Why would they not disclose it? The answer to both is probably the same reason that no one can actually buy a Phi on the market, trade secrets/competitive intelligence. I am willing to bet we have found the first time Intel put out some advanced, very very advanced actually, packaging tech.

All of that stuffed under the lid nicely explain the size, secrecy, and likely where all lot of the heat is coming from too. This technological marvel is likely painfully expensive to make too, a massive 22nm die with interposers and whatever else they slapped under the lid isn’t cheap. That said, Xeon Phis start at around $2000 so margins won’t be totally under water, but they are laughable compared to Intel’s GPU based competition.

And that is the real interesting thing we can discern from the picture, the cost. Intel can make transistors with technologies and geometries that no one else can come close to, that is not in doubt. They can package the result in ways that no other company can even attempt at the moment and do it in, err, painfully low volumes. What they can’t do is do it at a decent cost, and that is going to hurt them in the long run. And if Haswell GT3e/Crystalwell uses the same type of construction, what do you think that will mean for pricing? Now do you get it?S|A

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 Why is Intel so secretive about Phis die?

Charlie Demerjian

Roving engine of chaos and snide remarks at SemiAccurate
Charlie Demerjian is the founder of Stone Arch Networking Services and SemiAccurate.com. SemiAccurate.com is a technology news site; addressing hardware design, software selection, customization, securing and maintenance, with over one million views per month. He is a technologist and analyst specializing in semiconductors, system and network architecture. As head writer of SemiAccurate.com, he regularly advises writers, analysts, and industry executives on technical matters and long lead industry trends. Charlie is also a council member with Gerson Lehman Group.