Archives for the month of: March, 2012

Price, cost comparisons between Apple’s A5X versus Intel’s processors

According to Chipworks, the A5X processor in the new iPad measures 12.82 mm x 12.71 mm for an area of 162.94 mm². iSuppli estimates that Apple is paying Samsung $23 to manufacture the chip. It becomes very surprising when you compare this to Intel’s Core i5 processor for laptops with 149mm² die area that sells for $225. Apple gets a 162.94 mm² chip for $23, Intel sells a 149mm² chip for $225. If the cost estimate from iSuppli is true, I think it shows that Intel has a huge margin for its processors and/or Apple might be getting a pretty good deal from Samsung (basically Samsung’s foundry margins are low). Intel’s margin gets even crazier for processors in higher-performing laptops such as the Intel Core i7 2960XM that measures 216mm² and sells for $1096. One thing to note is that the two Intel processors I mentioned here use 32nm, while Apple’s A5X uses 45nm, allowing Intel’s processors to fit in more functionality per unit area and charge higher prices (which is the reason Moore’s law keeps going on. Fit in more functionality per unit area, charge more for the same cost).

Why did iPad use two 512MB DRAM packages for 1GB memory?

Looking at the teardown image from iFixit, you can see that the iPad contains two DRAM packages (in yellow square) for a total of 1GB memory.

Compare this to Samsung’s Galaxy Tab 10.1, that has the same total memory of 1GB, but instead uses a single package (image from TechRepublic). The DRAM package is the black one right above the green Tegra three processor.

Using a single package 1GB DRAM would save PCB area, but I think there might be two problems. First, it might cost more than using two 512MB packages. Second, a 1GB DRAM package might be thicker than a 512MB package if the 1GB stacks larger numbers of DRAM dies in a single package. Maybe Apple had  enough PCB area to fit in two DRAM packages and made the decision based on cost. Maybe Apple was willing to use more PCB area to reduce thickness by placing two thinner 512MB packages side-by-side.

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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.”

Here are some thoughts on the new iPad based on discussions with my colleagues and advisors.

How did Apple fit in a 1.7x larger battery in the new iPad?

The new iPad’s battery capacity is 42.5Whr, a 1.7x increase compared to 25Whr of the iPad 2. Battery capacity is basically area x battery thickness, so either the area or the thickness has to increase to fit in a 1.7x larger battery. Tablet thickness increased only 0.6mm, from 8.8mm to 9.4mm. For now, let’s assume the battery area is the same and the 0.6mm increase in tablet thickness all came from the battery. Battery thickness in the iPad 2 was 2.5mm, giving the new iPad a 3.1mm thick battery, resulting in a 1.24x increase in battery capacity, far smaller than 1.7x. This means that the battery thickness might have increased by more than 0.6mm. Maybe the new iPad uses a thinner glass for the display, leaving more room to increase battery thickness. If the battery area is the same, battery thickness in the new iPad would be 2.5mm x 1.7 = 4.25mm, meaning that Apple somehow shaved off over 1mm in thickness from other components such as the display, glass, aluminum body etc.

Another possibility is that battery area increased. However, the following teardown photo of the iPad 2 from iFixit shows that there is really not much room to increase the battery area.

The black part is the battery and the top part covered by aluminum shields is the PCB that contains all the chips (processors, DRAM, Flash memory etc). The battery already occupies the majority of the area compared to the small PCB. White space on the top right corner is left for the 3G module that contains chips for 3G communication (the iPad 2 in the picture is a WiFi version, hence no 3G module). Since the PCB and battery are placed side-by-side, the PCB area has to get smaller to increase battery area. However, the image below, a zoom-in on the PCB with the shields taken off, shows that the PCB is already pretty tight on space.

You can see that there is not much space to shave off in the PCB. The white space next to the orange square (NAND flash chip) is left for another NAND flash chip for the 32GB version (image shows a 16GB version). It seems it would have been very difficult to increase battery area and thickness, but Apple somehow pulled it off. Hopefully iFixit will soon release teardown images of the new iPad that reveals how Apple could fit in a 1.7x larger battery.

Battery life is the same despite a 1.7x larger battery

According to tech specs on the Apple website, both the new iPad and iPad 2 have up to 10 hours of battery life in WiFi mode. This means that the new iPad consumes 1.7x more power than iPad 2. Where is this additional power consumption coming from? It’s not coming from 4G since the battery life is for WiFi mode. Maybe it is coming from the higher resolution display. Assuming 1.7x more power is entirely coming from additional display power and that display power was ~50% of the total power consumption of the iPad 2, display power would have to be 2.4x larger in the new iPad. Does this make sense? Display power consists of backlight power and TFT switching power. Assuming backlight power does not change based on the display resolution, the power difference is from the TFT switching power that increases proportionally with display resolution. Basically, backlight power stays the same, but TFT switching power increases by 4x in the new iPad. A 2.4x increase in display power is possible if the TFT switching power was ~50% of the total display power in the iPad 2. Another possibility is that the processor power increased due to bigger graphics in the A5X compared to A5.

New package for A5X

The A5X processor in the new iPad seems to use a metal-ish material for the package compared to the A5 chip in the iPad 2. Maybe Apple changed the package material for better thermal conductivity because of higher power consumption in the A5X processor.

No iPad 3

Seems Apple is no longer putting numbers in iPad models. It’s now just a “new iPad” or “iPad 2012”, just like how Apple calls their macbook and iMac models. Maybe they are running out of new things to add to the iPad. Customers tend to expect a significant design overhaul when the model number changes, so Apple might be preparing for the time when there is no significant changes in consecutive iPad models. It could also be related to not wanting to sell prior models at a cheaper price.  Currently, Apple sells older models like the iPhone 3GS, iPhone 4, iPad 2 at a cheaper price. They don’t do this for the Macbook models. The previous models just disappear when new models are released. Maybe Apple wants to expand this to the iPhone and iPad lines.

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