Patent Applications Reveal Apple's Research Into 3D Chip Packaging

Apple's persistent quest for better performance, longer battery life, and slimmer form factors appears to be driving its research into advanced chip packaging technologies. So-called "2.5D" and "3D" packaging methods stand to offer significant gains in all of these areas by increasing memory bandwidth, reducing power consumption, and freeing up space for higher-capacity batteries.

Apple has been an aggressive adopter of new device packaging methods, mostly thanks to integrated fan-out (InFO) innovations provided by foundry partner TSMC. TSMC's success has spurred it into further developing and diversifying its packaging offerings, and TSMC has emerged as an industry leader in packaging techniques.


While versions of TSMC's InFO packaging have brought performance improvements to Apple devices, such as better thermal management and improved package height, it has largely not been a direct enabler of improved electrical performance. This is set to change with future packaging techniques and is already seen in some products that utilize interposers for higher density interconnects to on-package memory, such as High Bandwidth Memory (HBM).

The primary memory candidate for inclusion in such a package would be conforming to the Wide I/O set of standards described by JEDEC, and mentioned by name in several of the patents. This memory improves on LPDDR4 by increasing the number of channels and reducing the transfer speed per channel, thus increasing the overall bandwidth but lowering the energy required per bit.

Interposers do, however, pose several issues for mobile devices. Significantly, they introduce another vertical element to the package, increasing total height. Interposers must also be fabricated on silicon wafers just like active ICs, with their dimensions driven by the footprint of all devices that need to be included in the package. These solutions are typically termed as "2.5D" due to some components being placed laterally with respect to one another rather a true stacking of chips.

Rather than adopt interposers for its products as a next step in advanced packaging, the direction of Apple's focus, according to several patent applications [1][2][3][4], appears to be on true "3D" techniques, with logic die such as memory being placed directly on top of an active SoC. Additionally, a patent application from TSMC seems to suggest a level of coordination between Apple and TSMC in these efforts.

3D stacking process flow

The process has similarities to the existing InFO techniques in that they both involve a redistribution layer (RDL) where contacts on a logic die are routed inside a molding compound with the help of vias directly in the molding compound. Where the 3D process diverts from this is that there is now RDL content on both sides of the die, necessitating the use of through-silicon vias (TSV) directly in the logic die so that interconnections can be made with the top of the die. A key feature of these RDL layers is that interconnect pitches finer than available substrate or interposer types is possible.

Subsequent dies could then be attached to the molding compound, mating with the vias and RDL placed in the previous step. This step could be done multiple times, provided each stacked component has TSVs for the next level of integration, and this is already seen in HBM, which allows for the stacking of up to eight DRAM dies.

Side view of memory die (110) attached to SoC (150) in 3D package

Still, this approach has many technical challenges that have prevented its commercialization. TSVs are expensive to implement and are a serious yield detractor to ICs. Electrical isolation from nearby components' radiated energy can also be a concern, particularly when integrating RF and analog components in a package with other components that would have been separated by space and EMI shielding before. Apple describes techniques to incorporate shielding directly in the package to mitigate this.

Package with integrated EMI shield

This approach also presents thermal challenges since active dies become so closely coupled in mediums that have poor thermal conductivity and shared thermal paths. These concerns extend not only to normal device usage, but also the package integration and any solder reflow steps. Thermal stresses can induce warpage of the packaging components due to differing coefficients of thermal expansion (CTE) amongst the materials utilized in the package. This warpage can lead to broken or separated contacts, resulting in device failure.

The use of a carrier substrate in the process flow mitigates some of the thermal concerns. The direct integration of heatsinks into device packaging is also addressed at various levels of the package assembly, such that higher dissipating die, such as a SoC featuring CPU and GPU cores, could be placed on the bottom of the stack or at a higher level of integration, providing stackup flexibility not seen in previous PoP arrangements.

Package with integrated heatsink component (310)

Embodiments may be applied in applications such as, and not limited to, low power and/or high I/O width memory architecture. Embodiments can enable a short double data rate (DDR) channel to neighboring function units (e.g. SOC, chipsets, etc.) by using RDL and direct chip attach. Embodiments may be particularly applicable for mobile applications that require low power DDR at target performance including high speed and I/O width.

The benefits of the methods described are many. The use of higher bandwidth memory will yield performance improvements. The flexibility of component placement shortens the distance between connected active and passive devices, either lowering the energy required to communicate between them, or reducing parasitic effects that can cause unwanted power loss or dynamic performance degradation. The most notable tasks that stand to benefit are gaming and image processing tasks, which often require large amounts of bandwidth over short time intervals.

Apple Watch Implications

These enhancements would be applicable to all of Apple's mobile devices, but multiple patent applications specifically mention methods of multiple components married together in a System in Package (SiP), as seen in the current Apple Watch. The methods described below are an enhancement on the existing SiP solutions found in Apple Watch in that they introduce true 3D stacking elements enabled by both TSV and Through Oxide Vias (TOV).

Array of TOVs for connecting stacked die to package pins

In one aspect, embodiments describe system on chip (SoC) die portioning and/or die splitting within an SiP structure (e.g. 3D memory package) in which IP cores such as CPU, GPU, IO, DRAM, SRAM, cache, ESD, power management, and integrated passives may be freely segregated throughout the package, while also mitigating total z-height of the package.

Additionally, the patent describes TSV and TOV pitch in explicit detail, suggesting that keeping package heights down allows them to create very small width vias, with the TOV forming interconnect rows at sizes smaller than even the TSVs. The effect of TSVs stressing active parts of the die, including hurting transistor performance, is also discussed, and the reduced pitches help to mitigate this.

Active die keepout zones around TSVs

Inclusion of RF transceivers and active devices on substrate types not currently used in Apple mobile devices are covered, indicating all types of active and passive components found in Apple Watch products could be housed in the SiP proposed.

Bottom level view of an SiP with stacked heterogenous die interconnected with TSV and TOV

Timeline

Packages featuring 2.5D and 3D connected components have been in consumer devices for several years, but most of the methods described above have yet to debut in mobile devices. The steps described are set to increase manufacturing complexity, and cost and throughput will likely suffer as a result.

Due to cost and yield concerns, a primary candidate for first inclusion of these methods would be a high-margin, low-quantity device. While the iPhone is the highest margin of Apple's mobile products, it is also the largest volume category, with a huge initial demand for each generation. The iPad Pro is a good candidate because of its low volume nature and its classification as a high-performance device. The inclusion of 120Hz refresh rate is something that will benefit from increased memory bandwidth, specifically.

The focus of many of these patents seems to be specifically on SiP methods seen in Apple Watch internals. The Apple Watch is a lower-volume device, and it stands to benefit because its internals are extremely sensitive to package size given the importance of its form factor and battery size. It seems reasonable to expect some of the methods described to be incorporated as soon as the next revision of the Apple Watch, and more progressively in future revisions.

Related Roundup: Apple Watch Series 6
Tag: TSMC
Buyer's Guide: Apple Watch (Buy Now)

Top Rated Comments

(View all)
Avatar
31 months ago
That's cool. I have no idea what I just read. But that's cool.
Score: 7 Votes (Like | Disagree)
Avatar
31 months ago
Just want to say thank you to MacRumors for posting this in-depth article. I appreciate articles that take the time to actually explain the science behind the ideas that have been patented and helps raise the level of discourse here.

TL;DR I'm glad it's not all just Apple VS. Samsung!
Score: 3 Votes (Like | Disagree)
Avatar
31 months ago
Keep the R&D focus! That's where the future is.
Score: 2 Votes (Like | Disagree)
Avatar
31 months ago

Yet we have people saying this is a copy of another patent and the patent office will make a mistake granting this.

the 1%.
Score: 2 Votes (Like | Disagree)
Avatar
31 months ago
Excellent write-up, MacRumors. Much appreciated, thanks!

Anandtech doesn’t really cover Apple any more so it’s nice you’re taking up that particular torch.
Score: 1 Votes (Like | Disagree)
Avatar
31 months ago

That's cool. I have no idea what I just read. But that's cool.

I understood integrated heatsinks into the chips themselves. That's all I understood.
Score: 1 Votes (Like | Disagree)

Top Stories

First Impressions From New iPhone 12 and 12 Pro Owners

Thursday October 22, 2020 4:20 pm PDT by
It's already Friday, October 23, in Australia and New Zealand, which means some customers who purchased an iPhone 12 or 12 Pro already have their new devices in hand. We've seen dozens of reviews of the iPhone 12 and iPhone 12 Pro from media sites, but now first impressions from regular Apple customers are available. Image via MacRumors reader Boardiesboi New iPhone 12 and 12 Pro owners are...

Early iPhone 12 Tests Show Ceramic Shield is Stronger and More Scratch Resistant Than iPhone 11 Glass

Friday October 23, 2020 1:21 pm PDT by
Apple's new iPhone 12 models are protected by a Ceramic Shield cover glass that has nano-ceramic crystals infused right into the glass to improve durability. According to Apple, Ceramic Shield offers four times better drop protection than the glass used for the iPhone 11 models. YouTube channel MobileReviewsEh conducted some tests on the iPhone 12 using a force meter to compare its performance ...

Apple Distributing New Heated Display Removal Machine for iPhone 12 Repairs

Thursday October 22, 2020 6:20 pm PDT by
Apple is providing Genius Bars and Apple Authorized Service Providers with a new heated display removal fixture for iPhone 12 and iPhone 12 Pro repairs, according to information obtained by MacRumors from a reliable source. To open iPhone 12 models, technicians will be required to slide the device into a specialized tray, and then place the tray into the high-temperature fixture for two...

Apple VP Kaiann Drance Interview Addresses Battery Life, MagSafe, and Power Adapter Concerns

Friday October 23, 2020 3:37 am PDT by
Apple's Vice President of iPhone Marketing, Kaiann Drance, has provided a new interview to Rich DeMuro on the Rich on Tech Podcast, to discuss the iPhone 12 and iPhone 12 Pro. Although much of the interview repeated points from Apple's "Hi, Speed" event, there were a number of interesting tidbits regarding the affect of 5G on battery life, MagSafe concerns, and the lack of a power adapter in...

Teardown Video Confirms iPhone 12 and iPhone 12 Pro Use Same 2,815mAh Battery

Thursday October 22, 2020 9:47 am PDT by
With the iPhone 12 launching on Friday and in just a few hours to Australia and New Zealand, hands-on videos, teardowns, reviews, and other iPhone-related content has been coming out. A new teardown video delves into both the iPhone 12 and the 12 Pro, confirming battery life for both models and giving us a closer look at their internals. The video from Io Technology is in Chinese, but ...

Images of Supposed AirPods Diagnosis Tool Shared Online

Thursday October 22, 2020 5:24 am PDT by
Apple is reportedly rolling out a new tool to Apple service providers for testing AirPods, according to leaker known as "Fudge," who shared images of the tool on Twitter. Apple appears to be seeking to reduce unnecessary AirPods services by more accurately diagnosing the cause of a fault. Instances of a dirt-blockage, which may be difficult to ascertain visually, can apparently be...

New Photos Offer Better Look at iPhone 12 Color Options

Tuesday October 20, 2020 2:34 am PDT by
As we wait for the iPhone 12 review embargo to lift later today, more pictures are circulating of the devices in real-world lighting conditions, providing a better look at the different colors available. Leaker DuanRui has shared images on Twitter of the iPhone 12 in white, black, blue, green, and (PRODUCT)RED. The black and white colors are similar to the iPhone 11 colors, but the other...

Apple's AirTags Revealed in Newly Published Patent Applications

Thursday October 22, 2020 9:13 am PDT by
Two patent applications filed by Apple appear to depict the company's widely expected AirTags item trackers (via Patently Apple). The filings, which include a large number of images, are titled "Mounting Base for a Wirelessly Locatable Tag" and "Fastener with a Constrained Retention Ring," and describe a wirelessly locatable tag that can be used to determine the absolute location of an...

iPhone 11 Pro Outlasts iPhone 12 and 12 Pro in Extensive Battery Life Test

Friday October 23, 2020 8:36 am PDT by
Arun Maini today shared a new side-by-side iPhone battery life video test on his YouTube channel Mrwhosetheboss, timing how long the new iPhone 12 and iPhone 12 Pro models last on a single charge compared to older models, with equal brightness, settings, battery health, and usage. All of the devices are running iOS 14 without a SIM card inserted. In the test, the iPhone 11 Pro outlasted both ...

Apple Warns MagSafe Charger Can Leave Circular Imprints on Leather Cases

Friday October 23, 2020 3:23 pm PDT by
If you keep your iPhone in a leather case while charging with Apple's new MagSafe Charger, the case might show circular imprints from contact with the accessory, according to a new Apple support document published today. Apple's leather cases for the iPhone 12 and iPhone 12 Pro are not available until November 6, but a MacRumors reader has already shared a photo of a circular imprint on...