Category Archives: Wafer Level Packaging

By Dr. Phil Garrou – Contributing Editor

3DIC memory, and therefore all of 2.5/3D technology, took one step closer to full commercialization last week with the HBM joint development announcement from AMD and Hynix at the RTI 3D ASIP meeting in Burlingame CA.

Suh Black, Kirby

Hynix Minsuk Suh, AMDs Byran Black and Microns Kyle Kirby debate the merits of HBM vs HMC at the 2013 RTI ASIP Conference

Bryan Black, Sr Fellow and 3D program manager at AMD noted that while die stacking has caught on in FPGAs and image sensors “..there is nothing yet in mainstream computing CPUs, GPUs or APUs” but that “HBM (high bandwidth memory) will change this.”  Black continued,  “Getting 3D going will take a BOLD move and AMD is ready to make that move.” Black announced that AMD is co-developing HBM with SK Hynix which is currently sampling the HBM memory stacks and that AMD “…is ready to work with customers.”

Minsuk Suh, principle engineer at Hynix confirmed that they are reading both 3D stacked memory for main memory and 3D stacked HBM for networking and graphics applications.   JEDEC specifications for these products are “mostly finalized.”

AMD Hynix 1

Suh indicated that the first application for HBM would be GPUs and that it will next move to networking and HPC applications. Initial details on the HBM processing sequence show a standard vias middle /carrier bonding / thin and via reveal / backside process / stack . TSV are on 40 micron pitch. HBM stacks show a 30% power reduction and a 37X size reduction over standard DDR4.

More details coming in future IFTLE blogs

EV Group (EVG), a supplier of wafer bonding and lithography equipment for the MEMS, nanotechnology and semiconductor markets, today announced that the Singapore-MIT Alliance for Research Technology (SMART) has ordered an EVG 850LT fully automated production bonding system designed for silicon-on-insulator (SOI) and direct wafer bonding using low-temp plasma activation processing.  SMART, which is a leading research center established by the Massachusetts Institute of Technology (MIT) in partnership with the National Research Foundation of Singapore, will utilize the EVG850LT system to support its advanced substrate development efforts.

The MIT research center is located outside the United States in Singapore and has five different research groups, including the Low Energy Electronic Systems (LEES) Research Group, which focuses on integrating silicon CMOS and compound semiconductor materials to enable new integrated circuits (ICs) for wireless devices, power electronics, LEDs, displays and other applications.  The LEES Research Group features a fabrication facility, where the EVG850LT has already been installed and is in use.

According to Professor Eugene Fitzgerald from MIT’s Department of Materials Science and Engineering, SMART chose the EVG850LT for the center’s advanced R&D efforts due to the system’s high process flexibility and performance, EVG’s experience in low-temperature bonding, and expertise and support in process development.

“The charter of our LEES Research Group is to identify new IC technologies that enable devices that consume less power, enable higher performance and open up new applications for information systems.  EV Group’s technology and expertise will play an important role in supporting this effort,” stated Professor Fitzgerald.

The EVG850 platform, upon which the EVG850LT system is built, is the only SOI and direct wafer bonding platform designed to operate in high-throughput, high-yield environments—establishing it as the industry standard in the SOI wafer bonding market.  The EVG850LT platform combines all essential steps for wafer bonding—from cleaning and alignment to pre-bonding and IR-inspection—in a single platform.  This ensures an ultra-clean production process throughout all stages to enable high-yield, void-free wafers, as opposed to stand-alone processing units that require the wafers to be manually transported in a regular cleanroom environment.  The EVG850 supports a variety of advanced substrates, including SOI and silicon on lattice engineered substrate (SOLES) technology, up to 300mm in diameter.

Global Industry Analysts, Inc. invites senior industry executives, domain experts, technologists and market strategists to participate in a comprehensive global research initiative studying the “Thin Films” markets. The study will examine key drivers and trends impacting the market such as growing interest in understanding atomistic properties of materials to discover newer ways to improve material performance; developments in thin film deposition technologies; innovation in material synthesis, processing, and computation; ever increasing performance requirements of optoelectronic components, semiconductor circuits, electric contacts, and coatings and the ensuing increased focus on advanced material research and nanotechnology; and expanding application areas such as in photovoltaics.

Defined as microscopic layers of material deposited onto metal, ceramic or plastic substrates, Thin Films are expected to witness strong demand in the integrated circuit industry. A technologically effervescent area of physics, thin films represents a branch of material science that marks the convergence of physics, electronic engineering, material science and metallurgy. Measuring less than one micron thick, thin films play an important role in the development of next generation semiconductor devices. Key application areas of thin films include communication, coating, microelectronics, optical electronics, and renewable energy generation systems, among others. The market is expected to benefit from the ever growing demand for smaller, miniaturized electronic devices with energy efficient high-speed computing performance. In this regard, thin film materials with new elemental composition, superconductivity, superior mechanical and dielectric strength, are poised to score the highest gains.

The growing focus on renewable energy against a backdrop of depleting fossil fuels and global warming, is forecast to drive demand for thin-film solar cell (TFSC), in turn benefitting the market for thin films. The continuous need to enhance the performance of medical devices will additionally generate demand for thin film coatings for medical equipment. The market is also forecast to witness the evolution of the new concept of growing thin films onto substrates as against the conventional deposition techniques. The trend of growing thin films is forecast to open up new growth avenues. Research is currently underway to explore methods to grow thin films of germanium crystals, the fruition of which can result in thin films replacing silicon in semiconductors. In the medium term however, growth in the market will largely benefit from advancements in deposition processes, improvements in surface characterization, and developments in nanomaterials, optical materials, organic thin films, magnetic thin films, and nano-metal oxide thin films, among others.

The study estimates Thin Films to be a multi-million dollar market worldwide, while more precise market-size and growth projections for a 14-year period will be made available during the 2nd stage of report preparation, and data analysis.

The research and analyses will be released shortly in the form of a comprehensive research report. The report by design, will attempt to provide exhaustive analysis, data, trends, market share, market size, statistics, forecasts and competitive intelligence. The report is modeled to offer precise and unbiased, actionable market insights including in-depth segmentation of market sub-sectors, demand estimates and projections and analysis of trends in each of the sectors, identification of leading players, and the competitive structure, among others.

Developed for Chip Designers, Fabricators, Manufacturers, Strategic Planners, Business Development Executives, Management Consultants, Investment Bankers, Consulting Firms, Marketing & Sales Executives, C-Level Decision Makers, Market Strategists and Technology Domain Experts, the report helps identify the biggest opportunities in this space and offers accurate latent demand forecasting that empowers quantitative decision making among existing market players and new entrants.

By Christian Gregor Dieseldorff, SEMI Industry Research & Statistics Group

SEMI’s World Fab Forecast report, published in November, predicts that fab equipment spending will decline about -9 percent (to US$32.5 billion) in 2013 (including new, used and in-house manufactured equipment).  Setting aside the used 300mm equipment GlobalFoundries acquired from Promos at the beginning of 2013 (NT$20-30 billion), fab equipment spending sinks further, to -11 percent in 2013.  The previous World Fab Forecast in August predicted an annual decline of just -1 percent (-3 percent without the used Promos 300mm equipment).

Fab equipment spending slowed in the third quarter much more than anticipated. The fourth quarter is also expected to be slower than previously thought, but will remain the strongest quarter of 2013. See figure 1.

Figure 1: Fab equipment spending for Front End facilities by quarter

Figure 1: Fab equipment spending for Front End facilities by quarter

2011 Still Record Year but 2014 Closing in

After two years of decline, the 2014 wafer fab equipment market is expected to grow over 30 percent.  Taiwan will be the strongest spending region with over US$9 billion, while Korea and the Americas will each spend at least US$6 billion each, and China and Japan will each spend around US$4 billion.

A growth rate of over 30% brings 2014 close to 2011 spending for wafer fab equipment. Comparing the actual spending numbers for 2014 and 2011, spending in 2014 is expected to be slightly below 2011 levels, about US$39.7 billion for 2011 compared to US$39.5 billion projected for 2014.

Fab Equipment Spending Patterns: Predicting the Next Slow Down?

The industry has displayed a predictable pattern for most of the past 15 years with regards to fab equipment spending: following two years of negative growth, there have been typically two subsequent years of positive growth. See figure 2.

Figure 2: Growth rates of fab equipment spending (2010 deliberately cut off in order to emphasize)

Figure 2: Growth rates of fab equipment spending (2010 deliberately cut off in order to emphasize)

According to the SEMI World Fab Forecast, in 2012 and 2013 the fab equipment market contracted, while the next two years, 2014 and 2015, are expected to be positive. The same scenario occurred from 2008 to 2011. After 2005, just a single year of a small decline, 2006 and 2007 showed growth. The same scenario occurred from 2001 to 2004. This pattern is not new and has been observed by many analysts.  However, over these 15 years, the industry has never experienced three consecutive years of growth or three years of decline according to SEMI database tracking.  At this point, the pattern points to expected growth in 2015, between 8 and 12 percent.  If the pattern holds, another decline will occur in 2016.

2013 — a Maverick Year

Semiconductor revenue growth is usually followed by more equipment spending, with revenue and capex typically riding the same rollercoaster.  This is not the case for 2013 as semiconductor revenues are expected to grow — although by single digits — equipment spending will not. See figure 3.

Figure 3: Change rates of semiconductor revenue and fab equipment spending (2010 deliberately cut off in order to emphasize)

Figure 3: Change rates of semiconductor revenue and fab equipment spending (2010 deliberately cut off in order to emphasize)

As demonstrated by the above chart, positive semiconductor revenue growth led to positive growth for fab equipment spending (except in 2005), while negative revenue years led to contractions in fab equipment spending. Industry consensus points to about 6 percent semiconductor revenue growth in 2013, though fab   equipment spending will contract. With the expected growth in semiconductor revenues for 2014, SEMI’s World Fab Forecast data support much stronger growth for fab equipment spending in 2014. The drop in 2013 may be explained by delays in ramping next generation products and a slower pace of new capacity addition.

Fab Construction Projects Strong in 2013 but Slowing

Across the industry, there are 40 major construction projects on-going in 2013, and 28 are predicted for 2014. Construction spending growth for 2013 is about 40 percent (US$7.5 billion). By 2014, this will drop by -15 percent (US$6.4 billion).  The largest construction projects already underway or expected to start soon are Samsung S3 (Line 17), Flash Alliance Fab 5 phase 2, possibly Globalfoundries Fab 8.2, Intel D1X module 2, and TSMC with four facilities. The World Fab Forecast report shows details per fab by quarter.

SEMI’s data support strong equipment spending in both 2014 and 2015, while construction spending is expected to decline in both years, and new capacity additions remain below 4 percent in 2014 and most likely in 2015 as well.

The SEMI World Fab Forecast lists about 1,150 facilities.  Since the last fab database publication at the end August 2013 SEMI has made 301 updates to 257 facilities (includiing Opto/LED fabs) in the database. The latest edition of the World Fab Forecast lists 1,149 facilities (including 250 Opto/LED facilities), with 67 facilities with various probabilities starting production this year and in the near future.Learn more about the SEMI fab databases at: www.semi.org/MarketInfo/FabDatabase and www.youtube.com/user/SEMImktstats

Can Intel beat TSMC?


November 25, 2013

By Zvi Or-Bach, president and CEO of MonolithIC 3D

Intel CEO Brian Krzanich, in the company Investor Meeting, presented company expansion focused on a foundry plan on Nov. 21, 2013. “You will see us focusing on a broader set of customers,” said Krzanich. “If somebody can use our silicon, and make computing better, than we want it to run better on Intel. It’s inclusive, it’s all-inclusive,” Krzanich added, as covered by Barron’s blog  Intel: Competitors Have Given Up ‘Scaling’ Advantage in Moore’s Law

Intel clearly believes that it can beat the pure play foundries by an ongoing reduction of transistor cost while improving performance and power with dimensional scaling – essentially maintaining the trend of Moore’s law just as in the past. Intel will “not take our foot off the pedal” of process technology, Krzanich explained, and he expects the company to be making parts as small as 10 nanometers in transistor size by 2015, versus today’s 22 nanometer parts. He was followed by Bill Holt, Intel’s EVP and head of semiconductor manufacturing, showing the following slide describing Intel expectations to drive down the cost per transistor.

Fig 1

Maintaining dimensional scaling is in-line with Holt’s previous slide presented at the Jefferies May 2013 Analyst Meeting:

Fig 2

Here we observe the first discrepancy where Intel says they are “continuing to scale while others are pausing to do FinFETS,” while the other foundries say that their transistor cost will not be reduced for nodes below 28nm. This was made very clear by GlobalFoundries in it recent seminars and is nicely illustrated in this ASML Semicon West 2013 slide:

Fig 3

This has also been generally accepted by analysts. Below is a slide from IBS’s Handel Jones presentation at the CEA-LETI day in June of this year:

Fig 4

Some may argue that Intel will have a hard time competing as a foundry due to potential customer concern of Intel as a competitor. This is a valid point, but it did not stop Apple to buy cell phone devices from Samsung.

Some may argue that Intel will have hard time competing due to the lack of broad EDA and IP support. This is also a valid point but Intel does not need to win all fabless designs. If Intel wins just the few super high volume designs, it may well win the war.

Some may argue that “Intel announced their high volume mobile SoFIA chips are mask fabricated at external foundry and do not use Intel internal manufacturing for at least next 2 years (2014-15). ALL of Intel’s production for standalone modem chips today is outside Intel. Conclusion being Intel still does not have the right silicon technology for mobile computing which is why X86 less than 0.1% of Smartphone market,” as one commenter at Intel Nears Foundry Inflection Point blog. This might be why Holt presented Intel’s plan to develop foundry-type processes.

“Those products were optimized primarily for performance, and so Intel had avoided the problem that can crop up when transistors are packed more densely, namely that performance of the wires connecting transistors, the interconnects, can degrade. We didn’t scale the wires as much as we could have, because the products we were building didn’t demand that.” Now, he said, “the company’s technology would be focused more on those interconnects as Intel takes the scaling lead. The result would be the ability to more nimbly move between transistors optimized for performance, on the one hand, as in server and desktop chips, and transistors optimized for low-power mobile devices.” as illustrated below:

Fig 5

It would seem that if Intel could scale transistor cost as they have done in the last 40 years then they could win these super high volume consumer-oriented designs where cost is extremely important. And TSMC is clearly taking this seriously. As was made public after they lost Altera to Intel, TSMC aligned itself to face head-on Intel’s challenge by expediting the development of FinFet technology.

As TSMC’s P/E is 14.42 while Intel’s P/E is only 12.87 the market should have responded very well to these presentations but apparently it did not — and in reverse to NASDAQ trend, Intel stock fell more than 5% the day after:

(Click to view full screen.)

(Click to view full screen.)

Nor did Altera’s stock perform well since announcing the move to Intel as a foundry, especially when compared to Xilinx who choose to stay with TSMC, as the stock price chart below illustrates:

(Click to view full screen.)

(Click to view full screen.)

The Stock market might be wrong, as it been wrong many times before, but then there are other concerns:

Why did Intel feel the need to put so much money in the ASML EUV program if they can do just as well without EUV? Does Intel reduced cost per transistor account for its escalating cost of R&D, which in 2013 averaged more than 20% of revenue vs. less than 14% in 2005? Does Intel reduced cost per transistor account for its escalating cost of capital, which, per their balance sheet on Depreciation/Depletion, averaged in 2013 more than 26% of revenue vs. less than 10% in 2011?

It is not clear what the Intel proprietary technology is that allows it to do so much better than the foundries to produce a per transistor cost reduction. It does seem that their fab equipment and especially lithography is the same. And it also unclear why the Intel per transistor costs are not impacted by the much higher cost of lithography with the double and quadruple litho steps needed in manufacturing these advanced process nodes and the extra development and process steps required.

There is one more important issue that seems to be ignored. For SoC applications, the embedded SRAM is a key factor because it dominates the die area, as we recently presented in our blog Are we using Moore’s name in vain? If Intel’s embedded SRAM is scaling each node as before, then it would represent an important advantage over the foundries. Yet Intel recently announced integration of DRAM into Haswell and promised future Xeon and Xeon Phi models that integrate memory atop processors in 3D packages instead. Will these be aggressive enough to keep the on-system memory costs scaling?

Fig 9

In short, if Intel could keep the traditional 30% cost reduction per node from 28nm to 10nm, and the foundry’s cost per transistor is staying flat, then Intel would be able to provide their foundry customers SoC products at a third of ther other foundries cost, and accordingly Intel should be able to do very well in its foundry business.

GLOBALFOUNDRIES today unveiled details of a project that demonstrates the value of its open and collaborative approach to delivering next-generation chip packaging technologies. The company, in partnership with Open-Silicon (chief architect) and Amkor Technology, Inc. (assembly and test), jointly exhibited a functional system-on-chip (SoC) solution featuring two 28nm logic chips, with embedded ARM processors, connected across a 2.5D silicon interposer. The jointly developed design is a test vehicle that showcases the benefits of 2.5D technology for mobile and low-power server applications and the viability of the Foundry 2.0 collaborative enablement model.

While some semiconductor manufacturers are approaching next-generation packaging technologies through internal development, GLOBALFOUNDRIES is enabling an open supply chain through collaboration with ecosystem partners and customers. This approach allows GLOBALFOUNDRIES’ customers to choose their preferred supply chain partners, while leveraging the experience of ecosystem partners who have developed deep expertise in design, assembly and test methodologies. When combined with GLOBALFOUNDRIES’ leading-edge manufacturing capabilities, this open and collaborative model is expected to deliver lower overall cost and less risk in bringing 2.5D technologies to market.

“As the fabless-foundry business model evolves to address the realities of today’s dynamic market, foundries are taking on increasing responsibility for enabling the supply chain to deliver end-to-end solutions that meet the requirements of the broad range of leading-edge designs,” said David McCann, vice president of packaging R&D at GLOBALFOUNDRIES. “To help address these challenges, we are driving our ‘Foundry 2.0’ collaborative supply chain model by engaging early with ecosystem partners like Open-Silicon and Amkor to jointly develop solutions that will enable the next wave of innovation in the industry.”

The test vehicle features two ARM Cortex-A9 processors manufactured using GLOBALFOUNDRIES’ 28nm-SLP (Super Low Power) process technology. The processors are attached to a silicon interposer, which is built on a 65nm manufacturing flow with through-silicon-vias (TSVs) to enable high-bandwidth communication between the chips.

Open-Silicon provided the processor, interposer, substrate, and test design, as well as the test and characterization of the final product. GLOBALFOUNDRIES provided the PDKs, interposer reference flow and manufactured both the 28nm ARM processors and the 65nm silicon interposer with embedded TSVs. Amkor provided the package-related design rules and manufacturing processes for back-side integration, copper pillar micro-bumping, and 2.5D product assembly. GLOBALFOUNDRIES and Amkor collaborated closely throughout the project to develop and validate the design rules, assembly processes, and required material sets.

The companies demonstrated first-time functionality of the processor, interposer, and substrate designs, and the die-to-substrate (D2S) process used by the supply chain resulted in high yields. The design tools, process design kit (PDK), design rules, and supply chain are now in place and proven for 2.5D interposer products from GLOBALFOUNDRIES, Amkor, and Open-Silicon.

“This project is a testament to the value of an open and collaborative approach to innovation, leveraging expertise from across the supply chain to demonstrate progress in bringing a critical enabling technology to market,” said Ron Huemoeller, senior vice president of advanced product development at Amkor Technology. “This collaborative model will offer chip designers a flexible approach to 2.5D SoC designs, while delivering cost savings, faster time-to-volume, and a reduction in the technical risk associated with developing new technologies.”

“We are pleased to be at the forefront of making 2.5D a reality with our foundry and OSAT partners,” said Dr. Shafy Eltoukhy, vice president of technology development at Open-Silicon. “This approach will allow designers to choose the right technology for each function of their SoC while simultaneously enabling finer grain and lower power connectivity than traditional packaging solutions along with reduced power budgets for next-generation electronic devices.”

SUSS MicroTec, a global supplier of equipment and process solutions for the semiconductor industry and related markets, has successfully installed an ELP300 excimer laser stepper to support next generation advanced packaging and 3D IC laser debonding applications at the Fraunhofer Institute for Reliability and Microintegration (IZM), Berlin. The ELP300 excimer laser platform is designed for high volume manufacturing and processing of 100mm to 300mm wafers. The platform provides two novel manufacturing technologies to Fraunhofer IZM used in advanced packaging and 3D applications: 1) Excimer ablation provides the means to directly create vias and microstructures to combat technical limitations of traditional photo-dielectrics and photolithography approaches and 2) laser debonding of 3D ICs and MEMS for a stress free, non-thermal and very cost efficient method to debond thin wafers off a carrier. The Excimer laser stepper enables the development of higher performance packages in the manufacturing of next generation semiconductor devices, but also provides a significant cost savings potential.

As part of the Fraunhofer-Gesellschaft, Fraunhofer IZM specializes in applied and industrial contract research. Fraunhofer IZM’s focus is on electronic packaging technology and the integration of multifunctional electronics into systems. With the new ELP laser system the Fraunhofer IZM will broaden his expertise in the field of thinfilm polymers. These polymers are an important building block in all wafer level packages. Currently the need of photosensitivity has limited the application of new polymers which are required for thinner devices and 3D stacking applications. With laser ablation completely new polymer systems can be used with enhanced mechanical, physical and chemical properties like lower curing temperature, lower stress, and lower thermal coefficient of expansion. In addition the laser system will give a much higher flexibility for temporary wafer bonding. Ultrathin wafers can be handled safely without damage even at processes which require temperatures above 300 C.

“The ELP 300 will revolutionize technology in wafer level packaging and 3-D integration” says Dr. Michael Toepper manager of WLP at Fraunhofer IZM. “The need of photosensitivity for thinfilm polymers has been a strong barrier for better mechanical properties which are essential for high reliability of electronic systems. In addition the whole process becomes much cheaper and also much more environmentally friendly due to less consumption of organic solvents and TMAH.

“We see high growth potential for this technology, especially in our core market of advanced packaging and the future growth market for 3D ICs,” says Frank P. Averdung, president and CEO of SUSS MicroTec.

STMicroelectronics and Yogitech, a provider of functional safety solutions, have signed an agreement to create a comprehensive package that will simplify the development and certification of safety-critical applications based on STM32 microcontrollers.

ST and Yogitech have agreed to develop a safety manual and software test libraries as a simple, quick, and effective means of detecting and flagging potentially dangerous failures in STM32 designs using tailored development tools from IAR Systems. Directed at a market estimated at over EURO400 million in Europe alone, the initiative aims at allowing engineers to choose from over 500 ST microcontrollers to create innovative and safe industrial products for factory-automation applications.

“The complexity of modern integrated circuits is such that the adoption of a black-box approach for safety analysis is no longer an option,” said Silvano Motto, CEO of Yogitech. “The development of the STM32 safety package takes advantage of fRMethodology, our patented white-box approach to address functional safety analyses of integrated circuits approved by TÜV SÜD and by many lead companies in multiple application domains like industrial and automotive.”

“Achieving stringent functional-safety certification on systems where STM32 is the main microcontroller is a very popular request within our industrial customer base,” said Jacky Perdrigeat, EMEA Marketing Vice President for Microcontrollers, STMicroelectronics. “The cooperation with Yogitech sets to speed up time-to-market for critical safety applications, strengthening our offering for the industrial- and factory-automation markets, which are key segments for the STM32 product family.”

The market-proven 32-bit STM32 ARM(R) Cortex(TM)- M microcontrollers combine high performance, real-time capabilities, digital signal processing, and low-power, low-voltage operation, while maintaining ease of development and extensive compatibility between devices, families and software.

FlipChip International announced today the 100% acquisition of Millennium Microtech (Shanghai) – (MMS), a provider of fully integrated semiconductor packaging and testing services situated in the Zhang Jiang Hi- Tech Park, Pudong New Area, Shanghai, China. The MMS name will be changed to FlipChip International.

FCI acquired a majority shareholding in MMS in July 2012 and have since worked diligently with the Chinese authorities over the intervening period to acquire the remaining shares. With 100% ownership of MMS, FCI also gains full ownership of the Joint Venture Bumping facility FCMS. Full ownership will allow FCI to further develop our Shanghai facility with transferred technologies in WLCSP and embedded die technology from FCI Phoenix. These will include our ChipsetT embedded die technology, our Spheron WLCSP, and our plated copper Spheron WLCSP processes.

The strategic 100% acquisition of MMS has extended the global footprint of FCI to offer existing and new customers turnkey services including wafer and final test. FlipChip International will offer the optimum technology for the coming generations of packaging required in the smart phone, tablet, medical and automotive industries. FlipChip International will also provide a complete range of packaging and testing services in Asia to complement the existing bumping and Wafer level Packaging services already associated with FCI in Phoenix, Arizona.

David Wilkie the FCI President and CEO said, “The acquisition of MMS and FCMS is an important part of FlipChip International’s plan to grow the Asian portion of our advanced packaging business. In our class 100 Shanghai bump facility we will add increasingly complex wafer bumping technologies, and offer our Asian customers improved cycle times due to the location near many wafer foundries. Our high volume capability will enable FCI to further develop advanced IC packaging solutions such as Spheron WLCSP and ChipsetT, while still supporting more traditional IC package assembly and test.”

At the recent ECTC conference, various presentations addressed silicon interposers for 2.5D (Shinko), CoWoS reliability (TSMC) and microbumping (imec).

Dr. Phil Garrou, Contributing Editor

Shinko and CEA Leti detailed their presentation entitled “Warpage Control of Silicon Interposer for 2.5D Package Applications.”

Large silicon-interposers when attached to an organic substrate can cause significant warpage problems. Shinko/Leti examined several warpage control techniques including:

  • Using a “chip first process” where chips are mounted on the interposer first vs “chip last process” where the silicon-interposer is mounted on the organic substrate first and chips are mounted onto the interposer last.
  • Using various underfill resins.
  • Using Sn-57Bi solder and thus lowering peak temperature 45-90 degree C. This reduced warpage after reflow to 75% of that using SAC305.

Warpage of silicon-interposer using three types of underfills for 0 level assembly (micro bumps) were investigated. Maximum warpage using U.F. A1, A2 and A3 were 108, 123 and 132mm, respectively. The lowest warpage was obtained at using U.F. A1. With U.F.A3, solder bump open failures were observed. The authors conclude that “using underfill material with low Tg and high storage modulus for 0 level leads to high reliability.”

TSMC and customer Xilinx presented “Reliability Evaluation of a CoWoS-enabled 3D IC Package” which used FEA to study the thermo-mechanical response of the interposer-based package during thermal cycle reliability stressing. Focus was especially on the fatigue failures of the C4 and BGA joints. Experimental data collected on CoWoS test vehicles were used to validate the FEM models. Parametric study of key package material and geometric parameters was performed to analyze their effects on C4 bump thermal cycle reliability. Package materials of interest include UF (underfill), lid and substrate, and the geometric parameters include lid thickness and C4 bump scheme.

Results showed that the CoWoS package using AlSiC lid has better C4 bump life than the CoWoS package using Cu lid. While a thicker lid has the higher stiffness and better co-planarity, the higher constraint from the thicker lid induces higher stress inside the package which negatively impacts C4 bump fatigue and the micro-bump Ti/Al delamination.

C4 bump layer underfill with Tg of 70°C or 120°C, were studied. The underfill with lower Tg has higher driving force to C4 bump fatigue. When temperature is above Tg, the underfill has much lower Young’s Modulus which has much lower capability to protect C4 bump; and therefore the underfill with lower Tg has higher driving force to C4 bump fatigue. On the contrary, the underfill with lower Tg has lower driving force to Ti/Al delamination in the micro-bump structure. The C4 underfill with lower stiffness can play as a buffer layer and results in lower driving force to Ti/Al delamination in microbump.

imec reported on “Key Elements for Sub-50μm Pitch Micro Bump Processes.” Scaling the microbump pitch from hundreds to a few tens of microns is not straightforward. Several process parameters need to be taken into account to allow a reliable Cu(Ni)Sn ubumping process. One of the challenges for fine pitch Cu(Ni)Sn stacking is to obtain a high bump uniformity. The non-uniformity prevents Cu and Sn from having good contact and subsequent intermetallic formation and increases the risk of underfill entrapment.

A bump scheme that offers better margin for alignment error is better based on a scheme where the size of top die bumps is smaller than the size of the bottom pads. For example it is better to achieve 20μm pitch with 7.5μm bump on 12.5μm pad than with 10μm bump and pad because equal bump and pad diameter can tolerate only 2μm misalignment whereas the 7.5μm/12.5μm bump/pad can tolerate 5μm. This is a significant difference when working close to the stacking tool’s limit of alignment accuracy.

Details on the plasma treatments necessary when attempting to plate into these fine featured plating resists are also discussed.