Apple files chip block stack patent
Beyond the A4
Apple has filed a patent application that supports the stacked-component design of its A4 chip used in the iPad and iPhone 4, and points to further future integration of multiple system components on the same die.
The filing , "Systems and methods for providing a system-on-a-substrate," describes methods for reducing the size of a device by combining — in the words of the application — "all of the components of the system on the same microchip."
And by "all," the application is rather inclusive: "The components of a system can include one or more of a processor, memory (e.g., RAM, SDRAM, DDR RAM, or ROM), CODEC circuitry, Input/Output ("I/O") circuitry, communication circuitry, accelerometers, capacitors, inductors, or any other suitable components."
Apple's A4 chip isn't quite as all-embracing. As the teardown junkies and part-suppliers at iFixIt  showed when they partnered with Chipworks  to deconstruct  Apple's ARM-based part, the A4 stacks two layers of RAM above the processor die in the A4's package:
The A4, cut in half: that grey slab on the bottom is the ARM chip, with two RAM slices on top (source: iFixIt )
This technique is essentially what Apple describes in the first, and simplest, iteration in its patent filing:
Simple: memory on top of a processor on top of a PCB, with more memory underneath
Apple's patent filing goes further, though. It foresees a time when far more components can be placed on the same die: hence the term "system-on-a-substrate."
In one "embodiment" — patentese for "example" — a substrate can combine multiple components such as any or all from those listed above. That substrate, packaged up as a single chip, can then sit on a flexible printed circuit board ("flex"), which can extend beyond the package to support other components:
Now we're getting somewhere: multiple components on the same substrate
The filing also envisions embodiments in which the substrate can support both a flex layer upon which, say, memory is installed, along with a series of other components combined into their own package:
Various embodiments — such as this one — mix and match components, flex, and substrate
The goal off all this mixing and matching and cramming and combining is component shrinkage. According to the filing, a printed circuit board may require traces that are 60 micrometers in width and spaced 60 micrometers apart, while a substrate can get away with 15/15 — that would allow, according to the filing, a four-layer, 0.2 millimeter–thick substrate to replace a six-layer, 0.5 millimeter–thick PCB.
In addition to a substrate's straightforward size advantages, the ability to stack components on top of one another — as is done in the A4 — provides another opportunity to shrink a part's footprint.
In handheld, pocketable devices, size does matter — and this patent filing describes a series of ways that Apple could pack more functions into smaller spaces. Whether such a straightforward idea as component-stacking and substrate-packing is patentable, however, remains to be seen. ®