In all the iPhones through the 5s, the Processor & DRAM memory are stacked on top of one another in whats called a Package on Package or PoP. This saves real estate, but limits the amount of heat that can be pulled out of the SoC. The same was true for the original iPad. But since iPad 2 the packaging has changed, the SoC is on one side of the Motherboard with a large Heat Sink attached to its top. The DRAM are located on the obverse side of the MB, under the shadow of the SoC and connected to it through the PCB.
Would be interesting to find out how it is for the iPhone Air.
Incidentally the second largest mfr.s of Tablets ( they still make the SoCs for Apple ) continues to package their own SoC and DRAM in Tablets just like in iPhones.
Wonder if it says anything about power consumption, temperature inside or sensitivity to temperature for the two groups of Designers.
The A7 and Elpida DRAM are in discrete packages next to each other, since the iPad has the luxury of more available real estate. This version of the A7 has a hefty heat sink cap on it, possibly a sign that it's running hotter than the iPhone version, and another argument for not using PoP.
Addendum : in theory the larger screens in Tablets compared to SmartPhones would require the GPUs to work harder, making the SoC run hotter. But would still like to understand the difference in Packaging used by Tablet mfr.s no. 1 and 2. Perhaps have to wait till the next Tablet by no. 2. They keep using ARM Mali GPUs. Or does Android in some way have less power hungry graphics ?
Tom at Chipworks speculated the heat sink was because Apple was cranking up the frequency on the A7 to 1.4 GHz so it is running warmer in the bigger tablet.
FYI, I think the POP that Chipmonk mentioned was a memory stack, separate from the A7. It would be interesting to get a teardown of any POP mempory stack in the iPad Air and comparisons of prior memory stacks Apple used.
Apple has wonderful designers and design tools. The way they convert power with ultra high efficiency and manage very low thermal, is wonderful achievement. This is true for iphone, ipad and mac books. It will be good to know what kind of design tools and design process they employ. Can any Apple veteran highlight these tools and processes?
Apple, like many large companies has a "no talk" policy about which EDA tools they use, and their general methodology, because they consider this a competitive advantage. Why let your competitor's know how to catch up to you?
It is quite an accomplishment to achieve a thinner iPad. Even performance stayed the same with just reduce the size of battery, the task wouldn't be easy. Now, the processor runs faster. Application performance will be improved. The rest of the features will likely be apps driven. Bluetooth 4.0 will be the focus of a lot of developers and company building ioT. iBeacon will no doubt open up a lot of opportunities. The near future will tell. :)
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