iFixit just posted a teardown analysis of the new iPad today. iFixit’s team flew all the way to Australia, the first country to release the iPad, camped out overnight in front of an Apple Store in Melbourne, and tore down the iPad right after they bought it. This is being professional =) There are several points I wanted to update from the previous post based on what I learned from the iFixit teardown analysis.

How did they fit in the 1.7x larger battery?

In my previous post, I mentioned that the battery is 1.7x larger compared to iPad 2 and was wondering how they fit that into a tablet that only grew 0.6mm in thickness. It turns out they increased both battery thickness and area, but battery density (capacity per volume) is stil the same. I highly doubt that battery density will change dramatically in the near future. As shown in the image, the iPad’s battery consists of 3 cells.

According to a Ars Technica article, each cell in the new iPad measures 125 x 65 x 4 mm compared to the iPad 2’s 108 x 63 x 2.7mm. Battery thickness increased by 1.3mm (2.7mm -> 4mm) while total tablet thickness increased by 0.6mm. This means that Apple was able to shave off 0.7mm somewhere else (possibly made the display and/or aluminum body thinner). Battery area also increased from 108 x 63mm to 125 x 65mm. You can see the length of the battery did not change much (63->65mm) since the length of the tablet  did not change, leaving no room for the battery to grow. It seems Apple was able to have the battery slightly eat into the area that was originally occupied by the PCB, increasing battery width from 108mm to 125mm. However, the image below shows that PCB area did not change all that much between the iPad 2 (top) and the new iPad (bottom), but the two might have slightly different scales since I copied and pasted two images from different sources and scaled them assuming they have the same length.

How did Apple fit more chips without increasing PCB area?

The new iPad contains several more chip packages than iPad 2.

  • DRAM increased from 0.5GB to 1GB. It seems the DRAM vendors could not fit 1GB in a single package, so the new iPad has two separate DRAM packages (yellow square in image above)
  • A5X is not a package-on-package (PoP): A5 processor in the iPad 2 used a PoP configuration, stacking the DRAM package on top of the A5 package to save PCB area. In the new iPad, there is no package stacked on top of the A5X processor. Instead, there is a spacer and thermal paste between the cover and die (image below). I believe these are for better thermal conduction due to the higher power consumption of the A5X processor. This is interesting because most mobile processor until now was cooled through the PCB, which is the bottom side of the processor package. Due to increasing processor power, cooling through the PCB is not enough and Apple had to take off the DRAM package on the top and replace it with materials to help cool down the processor.

Despite having two more packages (2 DRAM package + 1 A5X vs 1 A5 PoP) than iPad 2, the new iPad has a comparable PCB size because it uses both sides of the PCB. Using both sides increases the thickness of the PCB, but I think it is not a problem because  1) the PCB and battery are placed side-by-side and 2) the battery thickness increased, allowing the PCB to also be thicker without making the tablet thicker.

My ending questions are:

  • Is there any weight imbalance between the left and right side of the tablet due to the battery being on one side and the lighter PCB on the other? I suspect Apple would put a lot of effort into making the tablet not tilt towards one side. Maybe the PCB is too small to cause an imbalance.
  • Why didn’t the DRAM vendors put 1GB in single package? They already stack two DRAM dies for a 0.5GB memory. Why not stack four dies for 1GB? They stack around 8 dies for NAND flash memory chips, so stacking more than two seems definitely possible. Maybe cost and yield is an issue.
  • I wonder if Apple was able to put more battery in the iPad 2 without making it thicker, but simply did not do it. Putting in more battery would have enabled 10< hours battery life in the iPad 2. Maybe they did not want to make the new iPad look bad compared to the iPad 2, so intentionally put in limited battery in the iPad 2 even though they had more space. It’s much better to say “the new iPad has the same 10 hours battery life even with Retina display and 4G” than “the new iPad has 10 hours battery life compared to 16 hours for iPad 2 because of the display and 4G.”
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