MEMS and Sensors for Wearable Electronics: Packaging …thor.inemi.org/webdownload/2015/ICEP_2015/MEMS... · MEMS and Sensors for Wearable Electronics: Packaging and Assembly Considerations

© 2015 TechSearch International, Inc.

MEMS and Sensors for Wearable Electronics: Packaging

and Assembly Considerations

E. Jan VardamanPresident

TechSearch International, Inc.

www.techsearchinc.com


What’s Wearable Electronics?

• Wearable electronics not clearly defined

• Products for consumer/fitness, medical, communication and fashion– Smart bracelets such as Nike’s

FuelBand and other fitness products

– Products for wrist account for 34% of shipments

• Smart watches

• Wearable medical devices such as portable blood pressure monitors, calorie trackers, heart rate monitors, etc.

• Camera for action sports, etc.

• Glass-based products, more than just Google Glass


Apple’s iWatch Board: We Can’t Wait to See!!!

• Almost no leadframe packages

• Mostly area array packages

– FBGAs

– WLPs

• Expected to use WiFi module with WLP

• No board space available: Need greater use of WLP or System-in-Package (SiP)

Source: Apple.


Medical Devices

Source: IPDiA.

• Traditional medical implantables

• From fitness accessory to clinical tool

• Wearable technology to help senior citizens remain mobile and live independent lives

• Non-invasive wearable transdermal microsystems for continuous monitoring

• Textiles for muscle stimulation, continuous ECG monitoring, etc.

• Wearables with sensors for targeted clinical applications in disease treatment


Growth Drives MEMS and Sensors

• MEMS and sensors growth driven by growth in wearable electronics

• Many different packages for wearable electronics


Package Choices: Which Ones Do I Use?• Quad flat no-lead (QFN)

• Fine pitch ball grid arrays (FBGA) with laminate or flex circuit substrate

• Ceramic land grid array (CLGA)

• LGA (with laminate substrate), typically wire bond moving to flip chip

• Flip chip BGA (FC-BGA)

• Wafer level package (WLP)

• Fan-out WLP (FO-WLP)

• Stacked die package (WB, or FC and WB)

• Package-on-package (PoP)

– Memory stack in top package

– Logic in bottom package can be WB, FC, Embedded die, or FO-WLP

• System-in-Package (SiP)

• Integrated Passive Device (IPD)

WLPFO-WLP

FC-BGA

LGA module

PoP

QFN


No One Solution for Wearables• Packaging options (found in today’s products)

–BGA, FBGA

– Flex circuit CSP

– LGA (including MCM)

–Chip-on-board (COB)

–PoP

–Stacked die CSP

– Leadframe packages such as QFN, SOP, TSOP

–Ceramic packages

– Integrated passive devices

–WLP

–Embedded die

• Packaging options (emerging)

– FO-WLP

–MIS package (leadframe versions with mold compound as underfill and substrate)

–SiP

• Cost/Performance trade-off determines adoption, but Costand Form Factor are key


MEMS Found in Wearable Electronics

• Accelerometers and Gyroscopes for motion sensing

• Pressure sensors

• High precision light sensors to accurately measure blood flow

• Sensors to accurately calculate heart rate

• Blood pressure monitors (need higher accuracy)

• Pulse monitors for runners etc.

• Others……..

MEMS Accelerometer

STMicroelectronics


Recent MEMS Developments

• Wafer level technology being adopted

– Cavendish Kinetics with its RF MEMS tuning solution for LTE smartphones and wearable devices using STATS ChipPAC WLP for small form factor

– Die thickness after back grinding 0.39 mm

– Total package height + solder ball 0.55 mm

– Lead count of 9

– 2X higher data rates and improved battery life (40%)

– Future RF antenna developments

• TSMC developments in MEMS

– SoC and MEMS in one chip (CMOS integration, deposition of material on top of silicon)

– Last year accelerometer (motion sensor)

– This year pressure sensors

– Future gyroscope

– Future monolithic microphone


MEMS Package Requirements

• Specialized interface with outside world and exposure to corrosive gases or fluids such as pressure sensors, fluidic devices

• Vacuum packaging, hermeticity

• Protection from moisture-sensitive capacitive devices will get signal errors

• High-temperature operation, such as in-cylinder pressure sensors operating at 1,000°C

• Challenging assembly processes, such as wire bonding to vertical surfaces

• Sensitivity to vibration and shock during processing steps such as grinding or pick-and-place


MEMS Packaging ComplexityMany options and cost / performance considerations

Cavity or overmold?

Wire bond or flip chip?

Die attach method?

EMI shielding?

Laminate or leadframe?

Wire type, loop radius

and gage?

Molded-in stress?

Leaded or not?

Encapsulation?Green material?

Stacked die or

side-by-side?

How/what to test?

Source: Amkor Technology


Amkor MEMS & Sensor Packaging Evolution

DLP® courtesy of TI

Broad range of point solutions Focused platforms

Transition from

Custom Packaging to

High Volume

Manufacturing

ChipArray® -Cavity

MLF® -Cavity (in-line or FAM)

ChipArray® -Molded

MLF® -Molded

LF-Cavity (pre-mold or FAM)

WLCSP

Source: Amkor Technology


MEMS Reliability

• Failure modes and mechanisms are more complex

• Number of potential failure modes and mechanisms is larger

• Some failures, such as collisions or sticking of movable parts, are transient and thus hard to identify or locate

• Packages contain multiple components and MEMS device failure must be differentiated from an ASIC failure

• Failure criteria are device- and application-specific

• Standard destructive failure analysis can result in erroneous conclusions due to sample preparation problems, therefore physical analysis must often b combined with modeling to identify the most probable failure sites

• Monitoring instruments may be exposed to the loading conditions, such as temperature excursions, mechanical shock, or vibration, and may need to be checked for degradation themselves


Wearable Product Requirements?

• What are reliability requirements?– Lifetime?– Environmental exposure (UV light, sweat, stress,

washer/dryer, cleaning fluids, mud, dust, wafer, sunscreen, etc.)

• Fitness activity bands– Polymer encased electronics– Components must survive mold process

temperatures– Must withstand twist, bend, flex compression– Must not react with bodily and environmental fluids

• Printed circuit design require environmental protection– Thermal management– Shock and vibration– Electrostatic discharge (ESD)– Bodily and environmental fluids

• Fabrics for wearable electronics– Weaving of metallized yarns– Lamination of circuit boards– Examples T-shirt for muscle stimulation therapy

• Need special reliability tests– Drop test (is it shock proof?)– Thermal stress (simulation) – Is it moisture resistant?


Conductive Fabrics

• Knitting or weaving conductive threads into textiles– Metalized threads with allow of silver, copper, tin, nickel– Deposition or coating of conductive polymers– Printing conductive inks– UK’s NPL development of stretch nylon fabric processed using its

technology (nano-silver coating of fibers)

Source: NPL.


Wash Cycles (Cotton Jersey)

Source: NPL


Battery Life Remains Important!!!• Low-power designs for devices

– ARM promoting designs for wearables

• New developments in battery technology needed

– Alternatives to Li-ion battery

– More durable, safer, and smaller

• Energy harvesting (applications including battery charger)

– Examples such as SiliconReef (fabless company from Brazil) IC for 12V/24V applications integrated with battery charger

– Vibration energy harvesting IC with 3.3V output regulation and power tracking

• Many U.S. Universities working on 3D thin-film batteries including

– Purdue University, University of Michigan, Northwestern, Stanford, Rice, Notre Dame, University of Texas

• New flexible bendable battery J.Flex from Korean company Jenax

– Bend, fold, twist, or scrunch battery to fit almost any device or use scenario

– Can fold up to 200,000 times without degrading performance

Source: SiliconReef.


Conclusions

• Many different products

• Many different types of boards/substrates

• Many different package types (traditional MEMS packages vs. new packages required for wearable products)

• Need many different reliability tests

• Need new materials to achieve realization of future product designs

• Don’t forget importance of battery life

Documents

MEMS and Sensors for Wearable Electronics: Packaging …thor.inemi.org/webdownload/2015/ICEP_2015/MEMS... · MEMS and Sensors for Wearable Electronics: Packaging and Assembly Considerations