As readers of IFTLE might imagine, the recent headline "3M Claims new LED Lightbulb designed to burn for 25 years" caught my eye. The article went on to say that the bulb, which looks like a traditional incandescent, has a 25-year lifespan (at three hours of use per day) and a $25 price tag. 3M is betting the price won’t be a huge hurdle for consumers because competing LED bulbs "are priced closer to $45." They then repeated the infamous refrain: "LED light costs $1.63 per year to operate — a quarter of the cost of a traditional bulb. So even at $25, given its longevity, it still comes out where you save money over the life of the bulb."

The bulb uses 3M’s multilayer optical film, adhesives, and heat-management technology. They indicate that their marketing has determined that "prospective buyers are likely to be environmentally conscious and more affluent — similar to those who bought a Toyota Prius hybrid in 2006." IFTLE certainly agrees 100% with the last statement.

IFTLE has gone into great detail to show that it is the bulb that matters, not the expected life of the LED chip. If any of the components of the bulb are not rated for a 25-year lifetime the bulb should not be rated for this period of time. I checked the IFTLE BS meter for the merit of LED lightbulb ads and sure enough they rate just short of outright fraud.

As I shook my head in disbelief that this scam of the American public was continuing unabated, with no corrective information coming from the DOE or any other Government agency [yes that was said tongue in cheek], I got a collect call from old friend Lester Lightbulb. As you know Lester is sitting on death row in San Quentin [isn’t it fitting that California is the state that incarcerated him]. As he awaits the electric chair [pun intended] Lester reached out to admonish me for calling my recently failed CFL his "cousin" [see IFTLE 109: "2012 IEEE VLSI Conference ; Lester’s cousin CFLDies Prematurely"].

While I had him on the phone I thought you, the readers of IFTLE, would appreciate a direct interview with Lester.

IFTLE: Lester, of course we know that CFL and you are not related, we were just trying to link you, CFL and LED as part of the interior lighting family.

Lester: I’d like to thank IFTLE and its like-minded readers for supporting me as I await eradication from the face of the earth, but that dirtbag "quicksilver" is no family member of mine. Do you see a tungsten filament? NO. So he is certainly not related to me.

IFTLE: Quicksilver… is that his nickname?

Lester: Yes, that’s what all us incandescents call him — quicksilver is mercury and all the CFLs contain that highly toxic element. They are the least environmentally friendly source of light that we can use, which makes it quite ironic that those who claim they are trying to save the environment are about to eradicate me and use him. I guess you haven’t seen the latest headlines from Sweden have you?

IFTLE: No, please share them with us, Lester.

Lester: "CFLs creating ‘acute crisis’ in Sweden." In a series of articles the Swedish newspaper Svenska Dagbladet has reported on the large scale ongoing dumping of fluorescent bulbs (CFLs), and the dangers of released mercury that goes with it [link].

Mina Gillberg, former advisor to EU environment commisioner Margot Wallström is now regretting the consequences of their decision to switch to CFLs. "The motive for replacing incandescent bulbs with CFLs was to save electricity and thereby save the environment," but Gillberg now condemns the drive for CFLs as "absurd."

Sweden estimates that 200,000 CFLs are thrown into glass recycling bins per year. "‘This is a health risk for those who work with recycling and a risk that the environmental toxin spreads in the natural environment"…" Especially when the recycling bins are indoors, since mercury vaporizes at room temperature and contaminates the surrounding area."

IFTLE: So mercury or quicksilver is really that big a problem, Lester?

Lester: Mercury has long been recognized worldwide as a health hazard because its accumulation in the body can damage the nervous system, lungs, and kidneys, posing a particular threat to babies in the womb and young children. No one I have ever heard of, of any political persuasion, defends mercury.

The British government instructs households that "…if a compact fluorescent lightbulb is broken in the home, the room should be cleared for 15 minutes because of the danger of inhaling mercury vapour." Similar warnings are on US packaging where, as we have already discussed, the consumer is directed to contact the EPA for proper disposal procedures.

In 2009, timesonline [UK] reported extensively on the production of CFL in China, where "a heavy environmental price is being paid for the production of ‘green’ lightbulbs."

Tests on hundreds of Chinese employees found dangerously high levels of mercury in their bodies and many have required hospital treatment, according to local health officials in the cities of Foshan and Guangzhou. At the Nanhai Feiyang lighting factory in Foshan tests found 68 out of 72 workers were so badly poisoned they required hospitalization. In Jinzhou, 121 out of 123 employees had excessive mercury levels."

In 2008 Maine banned the disposal of CFL bulbs. In their tests CFLs were broken in a small/ moderate sized room and mercury concentrations in the room were continuously monitored. "Mercury concentration in the room air often exceeded the Maine Ambient Air Guideline of 300 ng/m³ for some period of time, with short excursions over 25,000 ng/m³, sometimes over 50,000 ng/m³, and possibly over 100,000 ng/m³ from the breakage of a single compact fluorescent lamp…. All types of flooring surfaces tested can retain mercury sources even when visibly clean….. Residual mercury in the carpeting has particular significance for children rolling around on a floor, babies crawling, or non mobile infants placed on the floor…. Vacuuming up the smaller debris particles in an un-vented room can elevate mercury concentrations over the MAAG in the room and it can linger at these levels for hours. And the vacuum can become contaminated by mercury such that it cannot be easily decontaminated." They indicated that the homeowner would have a decision on whether or not to "replace the carpet in the area where the bulb was broken."

Is anyone who is buying a previously owned home thinking about whether the carpet has been contaminated with mercury? And what that means to their small children?

So IFTLE, can you tell me why the world’s governments and the world’s self-described "environmentalists" are trying to eradicate the incandescant bulb and replace them with CFLs?

IFTLE: Lester, I think it’s all tied to the EPA. In 1990, EPA was given authority to control mercury and other hazardous air pollutants from major sources of emissions to the air. For fossil fuel-fired power plants, the amendments required EPA to conduct a study of hazardous air pollutant emissions. In 1999, EPA estimated that approximately 75 tons of mercury were found in the coal delivered to power plants each year and about two-thirds of this mercury was emitted to the air annually. In 2000, the EPA found that regulation of hazardous air pollutants, including mercury, from coal and oil-fired power plants was appropriate and necessary. Lester, don’t you think that this is a good thing? You can’t be for supporting mercury pouring into the atmosphere from our electric utilities, can you?

Lester: No, none of us are, but the electric utilities are taking steps to reduce mercury emissions from power plants as part of ongoing pollution prevention programs. In fact, existing control technologies for sulfur dioxide (SO₂), nitrogen oxides (NO_x), and particulate matter have reduced power plant mercury emissions by roughly 40 percent already. All of those nasty materials need to be scrubbed as does mercury, but notice I do not include CO₂…and don’t get me started on that, because CO₂ has gotten a worse bum rap than I have by the same ignorant environmentalists and corrupt scientists.

IFTLE: SOX, NOX and particuate reductions are all good things, Lester. I’m with you on the C0₂ emissions too, Lester. CO₂ rates a 5+ on my BS meter, but we shall discuss that scientific fraud another day.

Lester: Anyway, my point is that instead of justifying toxic quicksilver light bulbs by pointing a finger at how toxic power generation is, why not continue to use safe, non-toxic, incandescent light bulbs and work on cleaning up the effluent from our power plants?

IFTLE: Once again you make sense, Lester. Let’s take a few minutes to discuss one of my pet peeves: CFL longevity. It’s claimed that a CFL will last ten times longer than an incandescent [It says so right on the packaging]. When my CFL bulb recently burned out faster than my incandescent bulbs [see IFTLE 109, "2012 IEEE VLSI Conference; Lester’s cousin CFL Dies Prematurely"], several readers reported that they too had experienced less than 1 year lifetime from their CFL bulbs. Hmmmm…

Lester: The basic problem is that quicksilver bulb lifetime is impacted by how often the bulbs are turned on and off and their use temperature. Optimal use for a fluorescent light is to be left on all the time at temperatures between 50-80°F. Wikipedia indicates that "In the case of a 5-minute on/off cycle the lifespan of a CFL can be reduced to close to that of incandescent light bulbs" — which is exactly the result that you got!

Since a lot of light use in the home is less than five minutes (i.e., a trip to the bathroom; looking in a closet; quick night time trip to the kitchen; get tool out of the garage, etc.), a much more accurate statement for CFL packaging would be: "Lifetime is estimated at 250-10,000 hours depending on use."

The picture below is of a CFL that failed after 200 hours [link]. The electrolytic capacitor is bulging at the end, and it had ruptured its safety seal and leaked electrolyte; the heatshrink tubing around the inductor got so hot that it split; and the capacitors are all seriously discolored.

The only way to get the maximum life from any CFL is to keep the electronics as cool as possible — preferably well under the manufacturers’ recommendation of 50°F.

Homeowners will also be faced with the expensive requirement to replace all non-ventilated light fittings with new ones that have sufficient airflow to maintain a safe temperature for CFL use. Because such fittings must be installed by a licensed electrician (in most countries), this is another expense that is usually ignored.

Any potential saving in energy bills is gone … for quite a few years, until the cost of the fittings and their installation is amortized. There is also the enormous waste of replacing perfectly good light fixtures with new ones, so the environmental impact is also negative — probably by a large margin.

By the way, IFTLE, I saw that you threw your CFL bulb away with the garbage. Hope you won’t be doing that anymore after our little discussion on mercury!

IFTLE: Wow, Lester, that’s a lot to think about. Anything else you want to share with our readers?

Lester: Yes, I’d like them to read the 2009 NY Times "green blog" interview with Howard Brandston. He is the award-winning lighting designer who helped develop the nation’s first standards for energy-efficient building design.

Mr. Brandston accuses "energy zealots" of using "faulty science" to determine the efficiency of light bulbs. To quote Mr Branston: "The calculations used by the government and others promulgating or promoting use of CFLs is strictly mathematical conjecture and has nothing to do with reality."

When asked whether we shouldn’t be doing all we can to cut down the amount of power usage, he responded: "But hoping that lighting is going to make a major contribution [to the reduction of power usage] borders on ridiculous. The real areas that should be looked at that would make big gains are in all commercial office buildings. If they raised the temperature in the summer that they would cool to and lowered the temperature that they would heat to […] we would save more energy in a few months than all the lighting watts per square foot baloney that’s going on now."

Basically, IFTLE, his conclusions are the same as yours when you looked at how much lighting contributed to the overall power usage in your house: "If you’re trying to save energy, that isn’t the place to start." [see IFTLE 98: Lester the Lightbulb vs. CFL and LED: The saga continues]

IFTLE: Lester, as always it has been a pleasure. I sincerely hope we can turn things around and get you a pardon, for your good and the good of the country.

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For all the latest on 3DIC, advanced packaging and the exploits of Lester the Lightbulb stay linked to IFTLE…………………………

3DIC SEMI Standards

The Inspection and Metrology Task Force  of  the Semi 3D standards group, recently approved its first Standard ,SEMI 3D1, Terminology for Through Silicon Via Geometrical Metrology. SEMI 3D1 will provide a starting point for standardization of geometrical metrology for selected dimensions of through silicon vias (TSVs). Although different technologies can measure various geometrical parameters of an individual TSV, or of an array of TSVs, such as pitch, top diameter, top area, depth, taper (or sidewall angle), bottom area, and bottom diameter, it is currently difficult to compare results from the various measurement technologies as parameters are often described by similar names, but actually represent different aspects of the TSV geometry.

Sony Stacked Image Sensor

CMOS image sensors are used in a wide range of Sony products, including digital cameras, digital camcorders, DSLR cameras and Android based smartphones. Sony has focused on key traditional parameters such as increased pixel counts, improved resolution and higher speed. January 2012, Sony announced that it had successfully developed a 3D stacked CMOS image sensor complete with TSV. In place of the supporting substrate used in conventional back-illuminated CMOS image sensors, this image sensor stacks  the back-illuminated pixels layer onto chips containing the circuit section for signal processing which facilitates greater functionality and compactness. The new structure is positioned to become the next generation of back-illuminated CMOS image sensors.

Venky Sundaram of GaTech updated the audience on "Glass as an Ideal Material for Interposers, Packages and System Integration." The two interposer programs at GATech are focused on Low Cost Silicon Interposers and Packages (LSIP); (a) wafer based; (b) panel based and Low Cost Glass Interposers; (a) wafer based and (b) panel based
According to Sundaram glass has the following attributes:

Although glass does have its challenges:

•          Die-Die X-Y Spacing
       –      Fillet sizes and pad metallurgy and materials

•          Die-Die / Die-Substrate Joining
       –        Micro bump uniformity ; Method of Join ; Materials
•          Thermal and Power Management
       –        Use of Lids, Stiffeners and Passives
       –        Underfill/Resin bleed, adhesive compatibility
       –       Process assembly sequence and materials
•          Warpage Control
      –        Interposer warpage ; Substrate warpage
      –        Top die warpage – area density/distribution
•          Intermediate e-Test Points
      –        Process assembly sequence

Hybrid SSD memory stack with ReRAM and TSV

Perofessor Takeuchi of Chuo Univ described a hybrid SSD architecture using ReRAM and high capacity NAND flash memory.

When SSDs are used for servers in financial institutions, performance is hindered and power consumption increased because random access is dominant. This causes data to get split up if the size of the data packets are not of the appropriate size (minimum for NAND is 16Kb). Takeuchi’s memory stack combines a NAND flash memory and ReRAM. ReRAM is used as both cache and storage memories. To overwrite a small amount of data in the NAND flash memory, software transfers the page of data to the ReRAM so that data is not fragmented in the NAND flash memory.

(Click on any of the images below to enlarge.)

A prototype, tested on an emulator, showed that compared with existing SSDs which only use NAND, the hybrid memory stack achieves an 11X higher data writing performance, 93% lower power consumption and 6.9 times longer product life. This assumed that the controller, ReRAM and NAND flash memory were connected by TSV. Although this has been hyped up by several reporters, we should note that it is possible to achieve almost the same results without using TSV. The major gain of using the TSV appears to be a 14% decrease in energy required to write as shown in the comparative table below.  

It is proposed that SSD in data centers would have to be changed out about 7 times less thus reducing expenses.

It should be noted that in order to use  the hybrid SSD architecture for different applications, it is necessary to change the controlling software algorithms.

We have previously discussed the fact that  Micron has created an industry group to collaborate on the implementation of an open interface specification for a new memory technology called the Hybrid Memory Cube (HMC). [http://www.hybridmemorycube.org/]

The HMC is a stack of multiple thinned memory die sitting atop a logic chip bonded together using TSV. This greatly increases available DRAM bandwidth by leveraging the large number of I/O pins available through TSVs. The HMC requires about 10% of the volume of a DDR3 memory module. It is claimed that the technology provides 15X the performance of a DDR3 module, uses 70% less energy per bit than DDR3 and uses 90% less space than today’s RDIMMs. [see IFTLE 95 "3DIC – Time Flies When You’re Having Fun; Further Details on theMicron HMC…"; IFTLE 74 "The Micron Memory Cube consortium"]

The HMC device uses TSV technology and fine pitch copper pillar interconnect.  The DRAM logic, responsible for DRAM sequencing, refresh, data routing and error correction is placed in a  separate high performance logic die.  DRAM and logic are connected by thousands of TSV. The DRAM is a slave to the logic layer timing control.  The HMC was constructed with 1866 TSVs on a roughly 60um pitch. 

(Click on any of the images below to enlarge them.)

When the top chip and lower chip are joined the temp must be raised slightly (sticking process) to get the NCF to flow together. This holds the two chips in place.

Factors Controlling NCF

Namics reported on the parameters controlling NCF performance. One of the main issues with NCF has been voiding. Namics reports that one of the causes of voids is captured air which is generated when an IC connects to NCF. This relates to the flow of resin. They could decrease the voids by optimizing the minimum melting viscosity. Another type of void comes from volatilization of gases may occur from organic materials in the structure such as the substrate. They found that the higher minimum melting viscosity is, the more effectively this type of voids can be controlled. They also optimized the minimum melting viscosity, curability and flux-ability for good interconnection. When the minimum melting viscosity is too high, the connection is poor. When cure speed is too high, solder melting is blocked. They attempted to optimize flux activity, and found that gelling time, minimum melting viscosity and oxidation-reduction power need to be controlled.

Hitachi Chemical (HC) also reported on their attempts to optimize their NCF products. HC reports that The major requirements for processability are (1) NCF can be laminated to the bumped wafer without air trapping around the bumps and dicing lines; (2) In the process of back grinding, the wafer laminated with NCF can be grinded back side (opposite side of NCF) to thinner wafer without damage such as wafer crack and delamination of NCF; (3) the alignment mark or dicing pattern on the wafer can be recognized through NCF; (4) the NCF-laminated wafer can be diced without damage such as chip crack and delamination of NCF.

Issues and solutions are listed in the table below:

Compression Molding Compounds for Fan out WLP and MUF

Hitachi Chemical (HC) reported on their studies on using solid molding compounds for fan out WLP and molded underfill (MUF) . Currently, liquid molding compounds are mainly used for eWLB as encapsulant. Liquid molding compound issues include cost, warpage and high die stand-off caused by molding shrinkage.

HC shows that solid molding compounds has better wafer warpage results that liquid wafer warpage. Package warpage was almost flat over the temperature range tested.

High filler content is necessary for such molding compounds. Lower temp curing is also useful to lower warpage due to reduction in thermal shrinkage. Post mold cure is 150C for 1 hr.

Using solid molding compounds for MUF, flip chips can be molded/underfilled at 130 C / 250 sec.

Koyanagi-san and co-workers at Tohoku Univ have looked at the sue of NCF and compression molding for 3D integration using self assembling technology. They examined chips with 20 um pitch Cu-SnAg microbumps with bump height ~  6 um ( 3 um thick Cu and 3 um thick SnAg). The chips were self assembled face up on a carrier wafer. Then, the chips were transferred to the corresponding target wafer with microbump-to-microbump bonding through a NCF. The strength of temporary bonding was lower than the microbump bonding through the NCF, and thereby, the chips were removed from the carrier wafer and successfully transferred to the target wafer. After that, the target wafer having the chips bonded upside down on the wafer was packaged by a compression molding technique with a granular resin that covered all over the self-assembled chips to planarize the chip-on-wafer structure. Finally, the chips and the resin were simultaneously thinned from the backside of the chips.

For all the latest on 3DIC and advanced packaging (hopefully in a week or less) stay linked to IFTLE…………….